diff --git a/server/test/unit/utils/dataUtils.test.ts b/server/test/unit/utils/dataUtils.test.ts
index f4893fe03..01f102cca 100644
--- a/server/test/unit/utils/dataUtils.test.ts
+++ b/server/test/unit/utils/dataUtils.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, it } from "@jest/globals";
-import { getDateForRange, NormalizeData, NormalizeDataUptimeDetails } from "../../../src/utils/dataUtils.ts";
+import { getDateForRange, getDateFormat, NormalizeData, NormalizeDataUptimeDetails } from "../../../src/utils/dataUtils.ts";
 import type { GroupedCheck } from "../../../src/domain/checks/check.type.ts";
+import { DateRanges, type DateRange } from "../../../src/types/query.ts";
 
 // ── Helpers ──────────────────────────────────────────────────────────────────
 
@@ -29,20 +30,35 @@ describe("getDateForRange", () => {
 		["month", 30 * 24 * 60 * 60 * 1000],
 	])("returns now minus the %s window", (range, offsetMs) => {
 		const before = Date.now();
-		const result = getDateForRange(range as string);
+		const result = getDateForRange(range as DateRange);
 		const after = Date.now();
 
 		expect(result).toBeInstanceOf(Date);
-		expect(result!.getTime()).toBeGreaterThanOrEqual(before - offsetMs);
-		expect(result!.getTime()).toBeLessThanOrEqual(after - offsetMs);
+		expect(result.getTime()).toBeGreaterThanOrEqual(before - offsetMs);
+		expect(result.getTime()).toBeLessThanOrEqual(after - offsetMs);
 	});
 
-	it("returns undefined for 'all'", () => {
-		expect(getDateForRange("all")).toBeUndefined();
+	it("returns the epoch for 'all'", () => {
+		expect(getDateForRange("all")).toEqual(new Date(0));
+	});
+});
+
+describe("getDateFormat", () => {
+	it.each([
+		["recent", "%Y-%m-%dT%H:%M:00Z"],
+		["hour", "%Y-%m-%dT%H:%M:00Z"],
+		["day", "%Y-%m-%dT%H:00:00Z"],
+		["week", "%Y-%m-%dT00:00:00Z"],
+		["month", "%Y-%m-%dT00:00:00Z"],
+		["all", "%Y-%m-%dT00:00:00Z"],
+	])("returns the %s bucket format", (range, format) => {
+		expect(getDateFormat(range as DateRange)).toBe(format);
 	});
 
-	it("returns undefined for unknown ranges", () => {
-		expect(getDateForRange("fortnight")).toBeUndefined();
+	it("has a format for every member of DateRanges", () => {
+		for (const range of DateRanges) {
+			expect(getDateFormat(range)).toMatch(/^%Y-%m-%d/);
+		}
 	});
 });