diff --git a/__test__/utils/dateUtils.test.ts b/__test__/utils/dateUtils.test.ts
new file mode 100644
index 0000000..811e10a
--- /dev/null
+++ b/__test__/utils/dateUtils.test.ts
@@ -0,0 +1,38 @@
+import { getCalendarRange } from "../../src/utils/dateUtils";
+
+describe("getCalendarRange", () => {
+  it("Nov 2025 (5 weeks): 2025-10-27 to 2025-11-30", () => {
+    const { start, end } = getCalendarRange(
+      new Date("2025-11-01T00:00:00.000Z")
+    );
+    expect(start.toISOString().slice(0, 10)).toBe("2025-10-27");
+    expect(end.toISOString().slice(0, 10)).toBe("2025-11-30");
+  });
+
+  it("Dec 2025 (6 weeks): end Sunday 2026-01-04", () => {
+    const { start, end } = getCalendarRange(
+      new Date("2025-12-01T00:00:00.000Z")
+    );
+    expect(start.toISOString().slice(0, 10)).toBe("2025-12-01");
+    expect(end.toISOString().slice(0, 10)).toBe("2026-01-04");
+  });
+
+  it("Feb 2025 (short month): end Sunday 2025-03-02", () => {
+    const { start, end } = getCalendarRange(
+      new Date("2025-02-01T00:00:00.000Z")
+    );
+    expect(start.toISOString().slice(0, 10)).toBe("2025-01-27");
+    expect(end.toISOString().slice(0, 10)).toBe("2025-03-02");
+  });
+
+  it("sets boundary times correctly (start 00:00, end 23:59)", () => {
+    const { start, end } = getCalendarRange(
+      new Date("2025-11-01T00:00:00.000Z")
+    );
+    expect(start.getHours()).toBe(0);
+    expect(start.getMinutes()).toBe(0);
+    expect(start.getSeconds()).toBe(0);
+    expect(end.getHours()).toBe(23);
+    expect(end.getMinutes()).toBe(59);
+  });
+});
diff --git a/src/utils/dateUtils.ts b/src/utils/dateUtils.ts
index e1dab4b..86512e5 100644
--- a/src/utils/dateUtils.ts
+++ b/src/utils/dateUtils.ts
@@ -13,13 +13,22 @@ export function getCalendarRange(date = new Date()) {
   const diffToMonday = (dayOfWeekStart + 6) % 7;
   const startDate = new Date(firstOfMonth);
   startDate.setDate(firstOfMonth.getDate() - diffToMonday);
+  startDate.setHours(0, 0, 0, 0);
 
   const lastOfMonth = new Date(year, month + 1, 0);
-  const dayOfWeekEnd = lastOfMonth.getDay();
 
-  const diffToSunday = (7 - dayOfWeekEnd) % 7;
-  const endDate = new Date(lastOfMonth);
-  endDate.setDate(lastOfMonth.getDate() + diffToSunday);
+  // Calculate how many days from startDate to lastOfMonth
+  const daysFromStart = Math.floor(
+    (lastOfMonth.getTime() - startDate.getTime()) / (1000 * 60 * 60 * 24)
+  );
+
+  // Calculate number of weeks needed to cover all days (round up)
+  const weeksNeeded = Math.ceil((daysFromStart + 1) / 7);
+
+  // endDate is the Sunday of the last week (startDate + weeks * 7 - 1)
+  const endDate = new Date(startDate);
+  endDate.setDate(startDate.getDate() + weeksNeeded * 7 - 1);
+  endDate.setHours(23, 59, 59, 999);
 
   return {
     start: startDate,