diff --git a/apps/client/src/widgets/collections/calendar/event_builder.spec.ts b/apps/client/src/widgets/collections/calendar/event_builder.spec.ts
index 2c872a14e5..88299e8b65 100644
--- a/apps/client/src/widgets/collections/calendar/event_builder.spec.ts
+++ b/apps/client/src/widgets/collections/calendar/event_builder.spec.ts
@@ -1,4 +1,4 @@
-import { describe, expect, it } from "vitest";
+import { describe, expect, it, vi } from "vitest";
 import { buildNote, buildNotes } from "../../../test/easy-froca.js";
 import { buildEvent, buildEvents } from "./event_builder.js";
 import { LOCALE_MAPPINGS } from "./index.js";
@@ -148,7 +148,7 @@ describe("Promoted attributes", () => {
         expect(event).toHaveLength(1);
         expect(event[0]?.promotedAttributes).toMatchObject([
             [ "assignee", "Target note" ]
-        ])
+        ]);
     });
 
     it("supports start time and end time", async () => {
@@ -177,6 +177,86 @@ describe("Promoted attributes", () => {
 
 });
 
+
+describe("Recurrence", () => {
+    it("supports valid recurrence without end date", async () => {
+        const noteIds = buildNotes([
+            {
+                title: "Recurring Event",
+                "#startDate": "2025-05-05",
+                "#recurrence": "FREQ=DAILY;COUNT=5"
+            }
+        ]);
+        const events = await buildEvents(noteIds);
+
+        expect(events).toHaveLength(1);
+        expect(events[0]).toMatchObject({
+            title: "Recurring Event",
+            start: "2025-05-05",
+        });
+        expect(events[0].rrule).toContain("DTSTART:20250505");
+        expect(events[0].rrule).toContain("FREQ=DAILY;COUNT=5");
+        expect(events[0].end).toBeUndefined();
+    });
+
+    it("supports recurrence with start and end time (duration calculated)", async () => {
+        const noteIds = buildNotes([
+            {
+                title: "Timed Recurring Event",
+                "#startDate": "2025-05-05",
+                "#startTime": "13:00",
+                "#endTime": "15:30",
+                "#recurrence": "FREQ=WEEKLY;COUNT=3"
+            }
+        ]);
+        const events = await buildEvents(noteIds);
+
+        expect(events).toHaveLength(1);
+        expect(events[0]).toMatchObject({
+            title: "Timed Recurring Event",
+            start: "2025-05-05T13:00:00",
+            duration: "02:30"
+        });
+        expect(events[0].rrule).toContain("DTSTART:20250505T130000");
+        expect(events[0].end).toBeUndefined();
+    });
+
+    it("removes end date when recurrence is valid", async () => {
+        const noteIds = buildNotes([
+            {
+                title: "Recurring With End",
+                "#startDate": "2025-05-05",
+                "#endDate": "2025-05-07",
+                "#recurrence": "FREQ=DAILY;COUNT=2"
+            }
+        ]);
+        const events = await buildEvents(noteIds);
+
+        expect(events).toHaveLength(1);
+        expect(events[0].rrule).toBeDefined();
+        expect(events[0].end).toBeUndefined();
+    });
+
+    it("writes to console on invalid recurrence rule", async () => {
+        const noteIds = buildNotes([
+            {
+                title: "Invalid Recurrence",
+                "#startDate": "2025-05-05",
+                "#recurrence": "RRULE:FREQ=INVALID"
+            }
+        ]);
+
+        const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+        await buildEvents(noteIds);
+        const calledWithInvalid = consoleSpy.mock.calls.some(call =>
+            call[0].includes("has an invalid #recurrence string")
+        );
+        expect(calledWithInvalid).toBe(true);
+        consoleSpy.mockRestore();
+    });
+});
+
+
 describe("Building locales", () => {
     it("every language has a locale defined", async () => {
         for (const { id, contentOnly } of LOCALES) {
diff --git a/apps/client/src/widgets/collections/calendar/event_builder.ts b/apps/client/src/widgets/collections/calendar/event_builder.ts
index cd27a89a5b..92952ca68b 100644
--- a/apps/client/src/widgets/collections/calendar/event_builder.ts
+++ b/apps/client/src/widgets/collections/calendar/event_builder.ts
@@ -1,12 +1,14 @@
 import { EventInput, EventSourceFuncArg, EventSourceInput } from "@fullcalendar/core/index.js";
+import { dayjs } from "@triliumnext/commons";
 import clsx from "clsx";
+import { start } from "repl";
 import * as rruleLib from 'rrule';
 
 import FNote from "../../../entities/fnote";
 import froca from "../../../services/froca";
 import server from "../../../services/server";
 import toastService from "../../../services/toast";
-import { formatDateToLocalISO, getCustomisableLabel, getMonthsInDateRange, offsetDate } from "./utils";
+import { getCustomisableLabel, getMonthsInDateRange } from "./utils";
 
 interface Event {
     startDate: string,
@@ -127,9 +129,10 @@ export async function buildEvent(note: FNote, { startDate, endDate, startTime, e
 
         startDate = (startTime ? `${startDate}T${startTime}:00` : startDate);
         if (!startTime) {
-            const endDateOffset = offsetDate(endDate ?? startDate, 1);
-            if (endDateOffset) {
-                endDate = formatDateToLocalISO(endDateOffset);
+            if (endDate) {
+                endDate = dayjs(endDate).add(1, "day").format("YYYY-MM-DD");
+            } else if (startDate) {
+                endDate = dayjs(startDate).add(1, "day").format("YYYY-MM-DD");
             }
         }
 
@@ -150,7 +153,7 @@ export async function buildEvent(note: FNote, { startDate, endDate, startTime, e
 
         if (recurrence) {
             // Generate rrule string
-            const rruleString = `DTSTART:${startDate.replace(/[-:]/g, "")}\n${recurrence}`;
+            const rruleString = `DTSTART:${dayjs(startDate).format("YYYYMMDD[T]HHmmss")}\n${recurrence}`;
 
             // Validate rrule string
             let rruleValid = true;
@@ -164,13 +167,11 @@ export async function buildEvent(note: FNote, { startDate, endDate, startTime, e
                 delete eventData.end;
                 eventData.rrule = rruleString;
                 if (endDate){
-                    const diffMs = new Date(endDate).getTime() - new Date(startDate).getTime();
-                    const hours = Math.floor(diffMs / 3600000);
-                    const minutes = Math.floor((diffMs / 60000) % 60);
-                    eventData.duration = `${String(hours).padStart(2, "0")}:${String(minutes).padStart(2, "0")}`;
+                    const duration = dayjs.duration(dayjs(endDate).diff(dayjs(startDate)));
+                    eventData.duration = duration.format("HH:mm");
                 }
             } else {
-                throw new Error(`Note "${note.noteId} ${note.title}" has an invalid #recurrence string. Excluding...`);
+                throw new Error(`Note "${note.noteId} ${note.title}" has an invalid #recurrence string ${recurrence}. Excluding...`);
             }
         }
         events.push(eventData);