diff --git a/src/components/AgendaView.vue b/src/components/AgendaView.vue
index 9a26701..dc06740 100644
--- a/src/components/AgendaView.vue
+++ b/src/components/AgendaView.vue
@@ -27,19 +27,19 @@
           <v-list-item-title class="text-center text-medium-emphasis">No events in this period</v-list-item-title>
         </v-list-item>
       </template>
-      <template v-for="(dayEvents, date) in groupedEvents" :key="date">
+      <template v-for="(dayOccurrences, date) in groupedEvents" :key="date">
         <v-list-subheader>{{ formatAgendaDate(date) }}</v-list-subheader>
         <v-list-item
-          v-for="entity in dayEvents"
-          :key="entity.identifier"
-          @click="$emit('event-click', entity)"
+          v-for="occurrence in dayOccurrences"
+          :key="occurrence.key"
+          @click="$emit('event-click', occurrence.entity)"
         >
           <template #prepend>
-            <v-icon :color="getEventColor(entity)">mdi-circle</v-icon>
+            <v-icon :color="getEventColor(occurrence)">mdi-circle</v-icon>
           </template>
-          <v-list-item-title>{{ entity.properties?.label || 'Untitled' }}</v-list-item-title>
+          <v-list-item-title>{{ occurrence.entity.properties?.label || 'Untitled' }}</v-list-item-title>
           <v-list-item-subtitle>
-            {{ getEventProperties(entity).timeless ? 'All day' : `${formatEventDateTime(getEventProperties(entity).startsOn)} - ${formatEventDateTime(getEventProperties(entity).endsOn)}` }}
+            {{ occurrence.timeless ? 'All day' : `${formatOccurrenceTime(occurrence.startMs)} - ${formatOccurrenceTime(occurrence.endMs)}` }}
           </v-list-item-subtitle>
         </v-list-item>
       </template>
@@ -54,12 +54,14 @@ import type { EntityObject } from '@ChronoManager/models/entity';
 import type { CollectionObject } from '@ChronoManager/models/collection';
 import { EventObject } from '@ChronoManager/models/event';
 import { daysVisibleRange, shiftLocalDays } from '@/utils/dateRanges';
+import { occurrencesForRange } from '@/utils/occurrenceIndex';
+import type { CalendarOccurrence, CalendarOccurrenceIndex } from '@/types/occurrence';
 
 type CalendarEntity = EntityObject;
 type CalendarCollection = CollectionObject;
 
 const props = defineProps<{
-  events: CalendarEntity[];
+  occurrenceIndex: CalendarOccurrenceIndex;
   calendars: CalendarCollection[];
   currentDate: Date;
   initialSpan?: AgendaViewSpan;
@@ -126,32 +128,27 @@ const dateRangeLabel = computed(() => {
 });
 
 const groupedEvents = computed(() => {
-  const grouped: Record<string, CalendarEntity[]> = {};
+  const grouped: Record<string, CalendarOccurrence[]> = {};
   const { start, end } = dateRange.value;
-  
-  const filtered = props.events.filter((e): e is CalendarEntity => {
-    const startsOn = getEventProperties(e).startsOn;
-    if (typeof startsOn !== 'string') return false;
-    const eventStart = new Date(startsOn);
-    return eventStart >= start && eventStart < end;
+
+  const occurrences = occurrencesForRange(props.occurrenceIndex, {
+    startMs: start.getTime(),
+    endMs: end.getTime(),
   });
-  
-  const sorted = filtered.sort((a, b) => 
-    new Date(getEventProperties(a).startsOn || 0).getTime() - new Date(getEventProperties(b).startsOn || 0).getTime()
-  );
-  
-  sorted.forEach(entity => {
-    const dateKey = new Date(getEventProperties(entity).startsOn || 0).toDateString();
+
+  occurrences.forEach(occurrence => {
+    const dateKey = new Date(occurrence.startMs).toDateString();
     if (!grouped[dateKey]) {
       grouped[dateKey] = [];
     }
-    grouped[dateKey].push(entity);
+    grouped[dateKey].push(occurrence);
   });
   
   return grouped;
 });
 
-function getEventColor(entity: CalendarEntity): string {
+function getEventColor(occurrence: CalendarOccurrence): string {
+  const entity = occurrence.entity;
   const event = getEventProperties(entity);
   if (event.color) return event.color;
   const calendar = props.calendars.find(cal => cal.identifier === entity.collection);
@@ -166,8 +163,8 @@ function formatTime(date: Date): string {
   return date.toLocaleTimeString('en-US', { hour: 'numeric', minute: '2-digit' });
 }
 
-function formatEventDateTime(value: string | null): string {
-  return value ? formatTime(new Date(value)) : '';
+function formatOccurrenceTime(timestamp: number): string {
+  return formatTime(new Date(timestamp));
 }
 
 function formatAgendaDate(dateString: string): string {
diff --git a/src/components/CalendarView.vue b/src/components/CalendarView.vue
index 26c5b4b..5abaf99 100644
--- a/src/components/CalendarView.vue
+++ b/src/components/CalendarView.vue
@@ -9,7 +9,7 @@
     <MonthView
       v-if="view === 'month'"
       :current-date="currentDate"
-      :events="events"
+      :occurrence-index="occurrenceIndex"
       :calendars="calendars"
       @event-click="$emit('event-click', $event)"
       @date-click="$emit('date-click', $event)"
@@ -20,7 +20,7 @@
     <DaysView
       v-else-if="view === 'days'"
       :current-date="currentDate"
-      :events="events"
+      :occurrence-index="occurrenceIndex"
       :calendars="calendars"
       :initial-span="initialDaysSpan"
       @event-click="$emit('event-click', $event)"
@@ -32,7 +32,7 @@
     />
     <AgendaView
       v-else-if="view === 'agenda'"
-      :events="events"
+      :occurrence-index="occurrenceIndex"
       :calendars="calendars"
       :current-date="currentDate"
       :initial-span="initialAgendaViewSpan"
@@ -53,12 +53,13 @@ import { spanToDays, type AgendaViewSpan, type DaysViewSpan } from '@/types/span
 import type { EntityObject } from '@ChronoManager/models/entity';
 import type { CollectionObject } from '@ChronoManager/models/collection';
 import type { VisibleDateRange } from '@/types';
+import type { CalendarOccurrenceIndex } from '@/types/occurrence';
 import { daysVisibleRange, monthGridVisibleRange } from '@/utils/dateRanges';
 
 const props = defineProps<{
   view: 'days' | 'month' | 'agenda';
   currentDate: Date;
-  events: EntityObject[];
+  occurrenceIndex: CalendarOccurrenceIndex;
   calendars: CollectionObject[];
   initialDaysSpan?: DaysViewSpan;
   initialAgendaViewSpan?: AgendaViewSpan;
diff --git a/src/components/DaysView.vue b/src/components/DaysView.vue
index 6e926dd..de1369f 100644
--- a/src/components/DaysView.vue
+++ b/src/components/DaysView.vue
@@ -45,18 +45,18 @@
           <div class="all-day-events-overlay">
             <div
               v-for="segment in allDaySegments.segments"
-              :key="segment.entity.identifier"
+              :key="segment.occurrence.key"
               class="all-day-event"
               :class="{
                 'is-start': segment.isStart,
                 'is-end': segment.isEnd,
               }"
               :style="getAllDayEventStyle(segment)"
-              @click="emit('event-click', segment.entity)"
-              @mouseenter="emit('event-hover', { event: $event, entity: segment.entity })"
+              @click="emit('event-click', segment.occurrence.entity)"
+              @mouseenter="emit('event-hover', { event: $event, entity: segment.occurrence.entity })"
               @mouseleave="emit('event-hover-end')"
             >
-              <span v-if="segment.isStart" class="event-label">{{ segment.entity.properties?.label || 'Untitled' }}</span>
+              <span v-if="segment.isStart" class="event-label">{{ segment.occurrence.entity.properties?.label || 'Untitled' }}</span>
             </div>
           </div>
         </div>
@@ -73,22 +73,22 @@
           <div v-for="day in visibleDates" :key="day.toISOString()" class="day-column" :class="{ 'single-day': daysCount === 1 }">
             <div class="day-events" @click="handleDayClick($event, day)">
               <div
-                v-for="entity in getTimedEvents(day)"
-                :key="entity.identifier"
+                v-for="occurrence in getTimedEvents(day)"
+                :key="occurrence.key"
                 class="day-event"
-                :style="getEventStyle(entity)"
-                @click.stop="emit('event-click', entity)"
-                @mouseenter="emit('event-hover', { event: $event, entity })"
+                :style="getEventStyle(occurrence)"
+                @click.stop="emit('event-click', occurrence.entity)"
+                @mouseenter="emit('event-hover', { event: $event, entity: occurrence.entity })"
                 @mouseleave="emit('event-hover-end')"
               >
                 <template v-if="daysCount <= 3">
                   <div class="event-time">
-                    {{ formatEventDateTime(getEventProperties(entity).startsOn) }} - {{ formatEventDateTime(getEventProperties(entity).endsOn) }}
+                    {{ formatOccurrenceTime(occurrence.startMs) }} - {{ formatOccurrenceTime(occurrence.endMs) }}
                   </div>
-                  <div class="event-title">{{ getEventProperties(entity).label || 'Untitled' }}</div>
+                  <div class="event-title">{{ getEventProperties(occurrence.entity).label || 'Untitled' }}</div>
                 </template>
                 <template v-else>
-                  <div class="event-title-compact">{{ getEventProperties(entity).label || 'Untitled' }}</div>
+                  <div class="event-title-compact">{{ getEventProperties(occurrence.entity).label || 'Untitled' }}</div>
                 </template>
               </div>
             </div>
@@ -104,7 +104,6 @@ import { ref, computed, watch } from 'vue';
 import {
   startOfDay,
   getMultiDaySegments,
-  getTimedEventsForDate,
   type MultiDaySegment,
 } from '@/utils/calendarHelpers';
 import { shiftLocalDays } from '@/utils/dateRanges';
@@ -112,6 +111,8 @@ import { DAYS_VIEW_SPANS, spanToDays, type DaysViewSpan } from '@/types/spans';
 import type { EntityObject } from '@ChronoManager/models/entity';
 import type { CollectionObject } from '@ChronoManager/models/collection';
 import { EventObject } from '@ChronoManager/models/event';
+import { occurrencesForDay, occurrencesForRange } from '@/utils/occurrenceIndex';
+import type { CalendarOccurrence, CalendarOccurrenceIndex } from '@/types/occurrence';
 
 const ALL_DAY_EVENT_HEIGHT = 24;
 
@@ -120,7 +121,7 @@ type CalendarCollection = CollectionObject;
 
 const props = defineProps<{
   currentDate: Date;
-  events: CalendarEntity[];
+  occurrenceIndex: CalendarOccurrenceIndex;
   calendars: CalendarCollection[];
   initialSpan?: DaysViewSpan;
 }>();
@@ -205,7 +206,12 @@ const allDaySegments = computed(() => {
     return visibleDates.value.findIndex(d => startOfDay(d).getTime() === targetDay.getTime());
   };
   
-  return getMultiDaySegments(props.events, rangeStart, rangeEnd, daysCount.value, getColumnIndex);
+  const occurrences = occurrencesForRange(props.occurrenceIndex, {
+    startMs: rangeStart.getTime(),
+    endMs: shiftLocalDays(rangeEnd, 1).getTime(),
+  });
+
+  return getMultiDaySegments(occurrences, rangeStart, rangeEnd, daysCount.value, getColumnIndex);
 });
 
 function isToday(date: Date): boolean {
@@ -213,8 +219,8 @@ function isToday(date: Date): boolean {
   return date.toDateString() === today.toDateString();
 }
 
-function getTimedEvents(date: Date): CalendarEntity[] {
-  return getTimedEventsForDate(props.events, date) as CalendarEntity[];
+function getTimedEvents(date: Date): CalendarOccurrence[] {
+  return occurrencesForDay(props.occurrenceIndex, date).filter(occurrence => !occurrence.timeless);
 }
 
 function getEventProperties(entity: CalendarEntity): EventObject {
@@ -230,28 +236,22 @@ function getEventColor(entity: CalendarEntity): string {
 
 function getAllDayEventStyle(segment: MultiDaySegment) {
   return {
-    backgroundColor: getEventColor(segment.entity),
+    backgroundColor: getEventColor(segment.occurrence.entity),
     left: `calc(${segment.startCol} / ${daysCount.value} * 100% + 4px)`,
     width: `calc(${segment.span} / ${daysCount.value} * 100% - 8px)`,
     top: `${segment.lane * ALL_DAY_EVENT_HEIGHT}px`,
   };
 }
 
-function getEventStyle(entity: CalendarEntity) {
-  const event = getEventProperties(entity);
-
-  if (!event.startsOn || !event.endsOn) {
-    return { display: 'none' };
-  }
-  const startTime = new Date(event.startsOn);
-  const endTime = new Date(event.endsOn);
+function getEventStyle(occurrence: CalendarOccurrence) {
+  const startTime = new Date(occurrence.startMs);
   const start = startTime.getHours() * 60 + startTime.getMinutes();
-  const duration = (endTime.getTime() - startTime.getTime()) / (1000 * 60);
+  const duration = occurrence.durationMs / (1000 * 60);
   
   return {
     top: `${(start / 1440) * 100}%`,
     height: `${(duration / 1440) * 100}%`,
-    backgroundColor: getEventColor(entity),
+    backgroundColor: getEventColor(occurrence.entity),
   };
 }
 
@@ -265,8 +265,8 @@ function formatTime(date: Date): string {
   return date.toLocaleTimeString('en-US', { hour: 'numeric', minute: '2-digit' });
 }
 
-function formatEventDateTime(value: string | null): string {
-  return value ? formatTime(new Date(value)) : '';
+function formatOccurrenceTime(timestamp: number): string {
+  return formatTime(new Date(timestamp));
 }
 
 function formatWeekDay(date: Date): string {
diff --git a/src/components/MonthView.vue b/src/components/MonthView.vue
index 4954604..cf71607 100644
--- a/src/components/MonthView.vue
+++ b/src/components/MonthView.vue
@@ -2,12 +2,12 @@
 import { computed, ref, onMounted, onUnmounted } from 'vue';
 import {
   startOfDay,
-  daysDiff,
-  isMultiDay,
-  getSingleDayEventsForDate,
+  getMultiDaySegments,
   type MultiDaySegment,
 } from '@/utils/calendarHelpers';
 import { shiftLocalMonths } from '@/utils/dateRanges';
+import { occurrencesForDay, occurrencesForRange } from '@/utils/occurrenceIndex';
+import type { CalendarOccurrence, CalendarOccurrenceIndex } from '@/types/occurrence';
 
 const EVENT_HEIGHT = 22; // Height of each event row in pixels
 const MAX_VISIBLE_EVENTS = 3; // Maximum event rows to show before "+N more"
@@ -21,7 +21,7 @@ interface WeekData {
 
 const props = defineProps<{
   currentDate: Date;
-  events: any[];
+  occurrenceIndex: CalendarOccurrenceIndex;
   calendars: any[];
 }>();
 
@@ -113,7 +113,21 @@ const weeks = computed<WeekData[]>(() => {
     }
     
     // Get multiday segments for this week
-    const { segments, laneCount } = getMultiDaySegments(weekStart, weekEnd);
+    const occurrences = occurrencesForRange(props.occurrenceIndex, {
+      startMs: weekStart.getTime(),
+      endMs: new Date(
+        weekEnd.getFullYear(),
+        weekEnd.getMonth(),
+        weekEnd.getDate() + 1,
+      ).getTime(),
+    });
+    const { segments, laneCount } = getMultiDaySegments(
+      occurrences,
+      weekStart,
+      weekEnd,
+      7,
+      date => date.getDay(),
+    );
     
     weeksData.push({
       startDate: weekStart,
@@ -126,77 +140,9 @@ const weeks = computed<WeekData[]>(() => {
   return weeksData;
 });
 
-function getMultiDaySegments(weekStart: Date, weekEnd: Date): { segments: MultiDaySegment[]; laneCount: number } {
-  const segments: MultiDaySegment[] = [];
-  
-  // Filter multiday events that overlap this week
-  const multiDayEvents = props.events.filter(entity => {
-    if (!entity.properties?.startsOn || !isMultiDay(entity)) return false;
-    const eventStart = startOfDay(new Date(entity.properties.startsOn));
-    const eventEnd = startOfDay(new Date(entity.properties.endsOn));
-    return eventStart <= weekEnd && eventEnd >= weekStart;
-  });
-  
-  // Sort: longer events first, then by start date
-  multiDayEvents.sort((a, b) => {
-    const aStart = new Date(a.properties.startsOn);
-    const aEnd = new Date(a.properties.endsOn);
-    const bStart = new Date(b.properties.startsOn);
-    const bEnd = new Date(b.properties.endsOn);
-    const aDuration = daysDiff(aStart, aEnd);
-    const bDuration = daysDiff(bStart, bEnd);
-    if (bDuration !== aDuration) return bDuration - aDuration;
-    return aStart.getTime() - bStart.getTime();
-  });
-  
-  // Lane assignment
-  const lanes: boolean[][] = []; // lanes[lane][dayOfWeek] = occupied
-  
-  for (const entity of multiDayEvents) {
-    const eventStart = startOfDay(new Date(entity.properties.startsOn));
-    const eventEnd = startOfDay(new Date(entity.properties.endsOn));
-    
-    // Clamp to this week
-    const segStart = eventStart < weekStart ? weekStart : eventStart;
-    const segEnd = eventEnd > weekEnd ? weekEnd : eventEnd;
-    
-    const startCol = segStart.getDay();
-    const endCol = segEnd.getDay();
-    const span = endCol - startCol + 1;
-    
-    // Find available lane
-    let lane = 0;
-    while (true) {
-      if (!lanes[lane]) lanes[lane] = [false, false, false, false, false, false, false];
-      
-      let isFree = true;
-      for (let d = startCol; d <= endCol; d++) {
-        if (lanes[lane][d]) { isFree = false; break; }
-      }
-      
-      if (isFree) {
-        for (let d = startCol; d <= endCol; d++) lanes[lane][d] = true;
-        break;
-      }
-      lane++;
-    }
-    
-    segments.push({
-      entity,
-      startCol,
-      span,
-      lane,
-      isStart: eventStart >= weekStart,
-      isEnd: eventEnd <= weekEnd,
-    });
-  }
-  
-  return { segments, laneCount: lanes.length };
-}
-
 // Single-day events for a specific date
-function getSingleDayEvents(date: Date): any[] {
-  return getSingleDayEventsForDate(props.events, date);
+function getSingleDayEvents(date: Date): CalendarOccurrence[] {
+  return occurrencesForDay(props.occurrenceIndex, date).filter(occurrence => !occurrence.multiDay);
 }
 
 // Count hidden events (multiday beyond MAX + single day beyond remaining space)
@@ -215,7 +161,7 @@ function isToday(date: Date): boolean {
   return date.toDateString() === today.toDateString();
 }
 
-function getEventColor(entity: any): string {
+function getEventColor(entity: CalendarOccurrence['entity']): string {
   if (entity.properties?.color) return entity.properties.color;
   const calendar = props.calendars.find(cal => cal.identifier === entity.collection);
   return calendar?.properties?.color || '#1976D2';
@@ -265,15 +211,15 @@ function getEventColor(entity: any): string {
             <!-- Single-day events -->
             <div class="cell-events">
               <div
-                v-for="entity in getSingleDayEvents(cell.date).slice(0, MAX_VISIBLE_EVENTS - week.laneCount)"
-                :key="entity.identifier"
+                v-for="occurrence in getSingleDayEvents(cell.date).slice(0, MAX_VISIBLE_EVENTS - week.laneCount)"
+                :key="occurrence.key"
                 class="single-day-event"
-                :style="{ backgroundColor: getEventColor(entity) }"
-                @click.stop="$emit('event-click', entity)"
-                @mouseenter="$emit('event-hover', { event: $event, entity })"
+                :style="{ backgroundColor: getEventColor(occurrence.entity) }"
+                @click.stop="$emit('event-click', occurrence.entity)"
+                @mouseenter="$emit('event-hover', { event: $event, entity: occurrence.entity })"
                 @mouseleave="$emit('event-hover-end')"
               >
-                {{ entity.properties?.label || 'Untitled' }}
+                {{ occurrence.entity.properties?.label || 'Untitled' }}
               </div>
               <div 
                 v-if="getHiddenCount(cell, week.laneCount) > 0" 
@@ -290,24 +236,24 @@ function getEventColor(entity: any): string {
         <div class="multiday-overlay">
           <div
             v-for="segment in week.multiDaySegments"
-            :key="`${segment.entity.identifier}-${weekIndex}`"
+            :key="`${segment.occurrence.key}-${weekIndex}`"
             class="multiday-event"
             :class="{
               'is-start': segment.isStart,
               'is-end': segment.isEnd,
             }"
             :style="{
-              backgroundColor: getEventColor(segment.entity),
+              backgroundColor: getEventColor(segment.occurrence.entity),
               left: `calc(${segment.startCol} / 7 * 100% + 4px)`,
               width: `calc(${segment.span} / 7 * 100% - 8px)`,
               top: `${34 + segment.lane * EVENT_HEIGHT}px`,
             }"
-            @click.stop="$emit('event-click', segment.entity)"
-            @mouseenter="$emit('event-hover', { event: $event, entity: segment.entity })"
+            @click.stop="$emit('event-click', segment.occurrence.entity)"
+            @mouseenter="$emit('event-hover', { event: $event, entity: segment.occurrence.entity })"
             @mouseleave="$emit('event-hover-end')"
           >
             <span v-if="segment.isStart" class="event-label">
-              {{ segment.entity.properties?.label || 'Untitled' }}
+              {{ segment.occurrence.entity.properties?.label || 'Untitled' }}
             </span>
           </div>
         </div>
diff --git a/src/pages/ChronoPage.vue b/src/pages/ChronoPage.vue
index 61b3f3b..c5eb8e6 100644
--- a/src/pages/ChronoPage.vue
+++ b/src/pages/ChronoPage.vue
@@ -43,9 +43,9 @@ const {
   loading,
   calendars,
   taskLists,
-  filteredEvents,
   filteredTasks,
   collections,
+  occurrenceIndex,
 } = storeToRefs(chronoOperationsStore);
 
 const {
@@ -277,7 +277,7 @@ watch(() => route.fullPath, () => {
             v-if="!isTaskView"
             :view="calendarView"
             :current-date="currentDate"
-            :events="filteredEvents"
+            :occurrence-index="occurrenceIndex"
             :calendars="calendars"
             :initial-days-span="daysViewSpan"
             :initial-agenda-view-span="agendaViewSpan"
diff --git a/src/stores/chronoOperationsStore.ts b/src/stores/chronoOperationsStore.ts
index 5eaaa03..0b04980 100644
--- a/src/stores/chronoOperationsStore.ts
+++ b/src/stores/chronoOperationsStore.ts
@@ -10,6 +10,7 @@ import { useEntitiesStore } from '@ChronoManager/stores/entitiesStore'
 import { useServicesStore } from '@ChronoManager/stores/servicesStore'
 import { useImportStore } from '@ChronoManager/stores/importStore'
 import type { VisibleDateRange } from '@/types'
+import { buildOccurrenceIndex, occurrencesForRange } from '@/utils/occurrenceIndex'
 
 type ChronoEntityProperties = EventObject | TaskObject
 
@@ -44,6 +45,10 @@ export const useChronoOperationsStore = defineStore('chronoOperationsStore', ()
     return events.value.filter(event => visibleCalendarIds.includes(event.collection))
   })
   const filteredTasks = computed(() => tasks.value)
+  const occurrenceIndex = computed(() => buildOccurrenceIndex(filteredEvents.value))
+  const visibleOccurrences = computed(() => visibleRange.value
+    ? occurrencesForRange(occurrenceIndex.value, visibleRange.value)
+    : [])
 
   function setVisibleRange(range: VisibleDateRange) {
     if (
@@ -176,6 +181,8 @@ export const useChronoOperationsStore = defineStore('chronoOperationsStore', ()
     tasks,
     filteredEvents,
     filteredTasks,
+    occurrenceIndex,
+    visibleOccurrences,
     setVisibleRange,
     saveEntity,
     deleteEntity,
diff --git a/src/types/occurrence.ts b/src/types/occurrence.ts
new file mode 100644
index 0000000..8b20986
--- /dev/null
+++ b/src/types/occurrence.ts
@@ -0,0 +1,19 @@
+import type { EntityObject } from '@ChronoManager/models/entity'
+
+export interface CalendarOccurrence {
+  key: string
+  entity: EntityObject
+  occurrenceId: string | null
+  startMs: number
+  endMs: number
+  dayStartMs: number
+  durationMs: number
+  timeless: boolean
+  multiDay: boolean
+}
+
+export interface CalendarOccurrenceIndex {
+  byDay: Map<number, CalendarOccurrence[]>
+  byEntity: Map<string, CalendarOccurrence[]>
+  sorted: CalendarOccurrence[]
+}
diff --git a/src/utils/calendarHelpers.ts b/src/utils/calendarHelpers.ts
index db5b8b3..49110ae 100644
--- a/src/utils/calendarHelpers.ts
+++ b/src/utils/calendarHelpers.ts
@@ -3,8 +3,10 @@
  * Shared logic for multi-day event handling across calendar views
  */
 
+import type { CalendarOccurrence } from '@/types/occurrence'
+
 export interface MultiDaySegment {
-  entity: any;
+  occurrence: CalendarOccurrence;
   startCol: number;
   span: number;
   lane: number;
@@ -85,7 +87,7 @@ export function eventOnDate(entity: any, date: Date): boolean {
  * Used for rendering spanning events across columns
  */
 export function getMultiDaySegments(
-  events: any[],
+  occurrences: CalendarOccurrence[],
   rangeStart: Date,
   rangeEnd: Date,
   columnCount: number,
@@ -94,30 +96,28 @@ export function getMultiDaySegments(
   const segments: MultiDaySegment[] = [];
   
   // Filter multi-day/all-day events that overlap this range
-  const multiDayEvents = events.filter(entity => {
-    if (!entity.properties?.startsOn) return false;
-    if (!isAllDay(entity)) return false;
-    return eventOverlapsRange(entity, rangeStart, rangeEnd);
+  const rangeStartMs = startOfDay(rangeStart).getTime();
+  const rangeEndExclusive = startOfDay(new Date(rangeEnd));
+  rangeEndExclusive.setDate(rangeEndExclusive.getDate() + 1);
+
+  const multiDayEvents = occurrences.filter(occurrence => {
+    return occurrence.timeless
+      && occurrence.startMs < rangeEndExclusive.getTime()
+      && occurrence.endMs > rangeStartMs;
   });
   
   // Sort: longer events first, then by start date
   multiDayEvents.sort((a, b) => {
-    const aStart = new Date(a.properties.startsOn);
-    const aEnd = new Date(a.properties.endsOn || a.properties.startsOn);
-    const bStart = new Date(b.properties.startsOn);
-    const bEnd = new Date(b.properties.endsOn || b.properties.startsOn);
-    const aDuration = daysDiff(aStart, aEnd);
-    const bDuration = daysDiff(bStart, bEnd);
-    if (bDuration !== aDuration) return bDuration - aDuration;
-    return aStart.getTime() - bStart.getTime();
+    if (b.durationMs !== a.durationMs) return b.durationMs - a.durationMs;
+    return a.startMs - b.startMs;
   });
   
   // Lane assignment - track which days are occupied in each lane
   const lanes: boolean[][] = [];
   
-  for (const entity of multiDayEvents) {
-    const eventStart = startOfDay(new Date(entity.properties.startsOn));
-    const eventEnd = entity.properties?.endsOn ? startOfDay(new Date(entity.properties.endsOn)) : eventStart;
+  for (const occurrence of multiDayEvents) {
+    const eventStart = startOfDay(new Date(occurrence.startMs));
+    const eventEnd = startOfDay(new Date(occurrence.endMs - 1));
     
     // Clamp to visible range
     const segStart = eventStart < rangeStart ? rangeStart : eventStart;
@@ -156,7 +156,7 @@ export function getMultiDaySegments(
     }
     
     segments.push({
-      entity,
+      occurrence,
       startCol,
       span,
       lane,
diff --git a/src/utils/occurrenceIndex.ts b/src/utils/occurrenceIndex.ts
new file mode 100644
index 0000000..bf78d53
--- /dev/null
+++ b/src/utils/occurrenceIndex.ts
@@ -0,0 +1,117 @@
+import type { EntityObject } from '@ChronoManager/models/entity'
+import type { EventObject } from '@ChronoManager/models/event'
+import type {
+  CalendarOccurrence,
+  CalendarOccurrenceIndex,
+} from '../types/occurrence'
+import type { VisibleDateRange } from '../types'
+import { shiftLocalDays, startOfLocalDay } from './dateRanges'
+
+const MINIMUM_DURATION_MS = 1
+
+function eventTimestamp(value: string | null | undefined): number | null {
+  if (!value) return null
+
+  const timestamp = Date.parse(value)
+  return Number.isFinite(timestamp) ? timestamp : null
+}
+
+function occurrenceFromEntity(entity: EntityObject): CalendarOccurrence | null {
+  const event = entity.properties as EventObject
+  const startMs = eventTimestamp(event.startsOn)
+  if (startMs === null) return null
+
+  const parsedEndMs = eventTimestamp(event.endsOn)
+  const endMs = parsedEndMs !== null && parsedEndMs > startMs
+    ? parsedEndMs
+    : startMs + MINIMUM_DURATION_MS
+  const dayStartMs = startOfLocalDay(new Date(startMs)).getTime()
+  const lastOccupiedDayMs = startOfLocalDay(new Date(endMs - 1)).getTime()
+  const entityKey = String(entity.identifier)
+
+  return {
+    key: `${entityKey}:master`,
+    entity,
+    occurrenceId: null,
+    startMs,
+    endMs,
+    dayStartMs,
+    durationMs: endMs - startMs,
+    timeless: event.timeless === true || lastOccupiedDayMs !== dayStartMs,
+    multiDay: lastOccupiedDayMs !== dayStartMs,
+  }
+}
+
+function appendToDayBuckets(index: CalendarOccurrenceIndex, occurrence: CalendarOccurrence) {
+  const lastOccupiedDayMs = startOfLocalDay(new Date(occurrence.endMs - 1)).getTime()
+  let day = new Date(occurrence.dayStartMs)
+
+  while (day.getTime() <= lastOccupiedDayMs) {
+    const dayKey = day.getTime()
+    const bucket = index.byDay.get(dayKey)
+    if (bucket) bucket.push(occurrence)
+    else index.byDay.set(dayKey, [occurrence])
+    day = startOfLocalDay(shiftLocalDays(day, 1))
+  }
+}
+
+function sortOccurrences(occurrences: CalendarOccurrence[]) {
+  occurrences.sort((left, right) => (
+    left.startMs - right.startMs
+    || right.durationMs - left.durationMs
+    || left.key.localeCompare(right.key)
+  ))
+}
+
+export function buildOccurrenceIndex(entities: EntityObject[]): CalendarOccurrenceIndex {
+  const index: CalendarOccurrenceIndex = {
+    byDay: new Map(),
+    byEntity: new Map(),
+    sorted: [],
+  }
+
+  for (const entity of entities) {
+    const occurrence = occurrenceFromEntity(entity)
+    if (!occurrence) continue
+
+    index.sorted.push(occurrence)
+    index.byEntity.set(String(entity.identifier), [occurrence])
+    appendToDayBuckets(index, occurrence)
+  }
+
+  sortOccurrences(index.sorted)
+  for (const bucket of index.byDay.values()) sortOccurrences(bucket)
+
+  return index
+}
+
+export function occurrencesForDay(
+  index: CalendarOccurrenceIndex,
+  date: Date | number,
+): CalendarOccurrence[] {
+  const dayKey = startOfLocalDay(new Date(date)).getTime()
+  return index.byDay.get(dayKey) ?? []
+}
+
+export function occurrencesForRange(
+  index: CalendarOccurrenceIndex,
+  range: VisibleDateRange,
+): CalendarOccurrence[] {
+  if (range.endMs <= range.startMs) return []
+
+  const matches = new Map<string, CalendarOccurrence>()
+  let day = startOfLocalDay(new Date(range.startMs))
+
+  while (day.getTime() < range.endMs) {
+    for (const occurrence of index.byDay.get(day.getTime()) ?? []) {
+      if (occurrence.startMs < range.endMs && occurrence.endMs > range.startMs) {
+        matches.set(occurrence.key, occurrence)
+      }
+    }
+    day = startOfLocalDay(shiftLocalDays(day, 1))
+  }
+
+  const occurrences = Array.from(matches.values())
+  sortOccurrences(occurrences)
+  return occurrences
+}
diff --git a/tests/js/unit/occurrenceIndex.test.ts b/tests/js/unit/occurrenceIndex.test.ts
new file mode 100644
index 0000000..e2ed72c
--- /dev/null
+++ b/tests/js/unit/occurrenceIndex.test.ts
@@ -0,0 +1,90 @@
+import { describe, expect, it } from 'vitest'
+import type { EntityObject } from '../../../../chrono_manager/src/models/entity'
+import {
+  buildOccurrenceIndex,
+  occurrencesForDay,
+  occurrencesForRange,
+} from '../../../src/utils/occurrenceIndex'
+import { daysVisibleRange } from '../../../src/utils/dateRanges'
+
+function localIso(year: number, month: number, day: number, hour = 0): string {
+  return new Date(year, month, day, hour).toISOString()
+}
+
+function eventEntity(
+  identifier: string,
+  startsOn: string | null,
+  endsOn: string | null,
+  timeless = false,
+): EntityObject {
+  return {
+    identifier,
+    properties: {
+      startsOn,
+      endsOn,
+      timeless,
+    },
+  } as unknown as EntityObject
+}
+
+describe('occurrence index', () => {
+  it('normalizes and sorts event timestamps once', () => {
+    const later = eventEntity('later', localIso(2026, 5, 15, 13), localIso(2026, 5, 15, 14))
+    const earlier = eventEntity('earlier', localIso(2026, 5, 15, 9), localIso(2026, 5, 15, 10))
+    const invalid = eventEntity('invalid', 'not-a-date', null)
+    const index = buildOccurrenceIndex([later, invalid, earlier])
+
+    expect(index.sorted.map(occurrence => occurrence.entity.identifier)).toEqual(['earlier', 'later'])
+    expect(index.byEntity.get('earlier')?.[0]?.durationMs).toBe(60 * 60 * 1000)
+    expect(index.byEntity.has('invalid')).toBe(false)
+  })
+
+  it('places an overlapping event in each occupied day bucket', () => {
+    const overnight = eventEntity(
+      'overnight',
+      localIso(2026, 5, 15, 23),
+      localIso(2026, 5, 16, 1),
+    )
+    const index = buildOccurrenceIndex([overnight])
+
+    expect(occurrencesForDay(index, new Date(2026, 5, 15))).toHaveLength(1)
+    expect(occurrencesForDay(index, new Date(2026, 5, 16))).toHaveLength(1)
+    expect(index.sorted[0].multiDay).toBe(true)
+    expect(index.sorted[0].timeless).toBe(true)
+  })
+
+  it('honors an exclusive midnight end', () => {
+    const allDay = eventEntity(
+      'all-day',
+      localIso(2026, 5, 20),
+      localIso(2026, 5, 21),
+      true,
+    )
+    const index = buildOccurrenceIndex([allDay])
+
+    expect(occurrencesForDay(index, new Date(2026, 5, 20))).toHaveLength(1)
+    expect(occurrencesForDay(index, new Date(2026, 5, 21))).toHaveLength(0)
+  })
+
+  it('retrieves overlapping occurrences without duplicates', () => {
+    const spanning = eventEntity(
+      'spanning',
+      localIso(2026, 5, 14),
+      localIso(2026, 5, 18),
+      true,
+    )
+    const outside = eventEntity('outside', localIso(2026, 6, 1), localIso(2026, 6, 1, 1))
+    const index = buildOccurrenceIndex([outside, spanning])
+    const occurrences = occurrencesForRange(index, daysVisibleRange(new Date(2026, 5, 15), 2))
+
+    expect(occurrences.map(occurrence => occurrence.entity.identifier)).toEqual(['spanning'])
+  })
+
+  it('gives a zero-duration event a queryable minimum duration', () => {
+    const instant = eventEntity('instant', localIso(2026, 5, 15, 9), null)
+    const index = buildOccurrenceIndex([instant])
+
+    expect(index.sorted[0].durationMs).toBe(1)
+    expect(occurrencesForDay(index, new Date(2026, 5, 15))).toHaveLength(1)
+  })
+})