diff --git a/apps/mobile/src/relative-date.ts b/apps/mobile/src/relative-date.ts
new file mode 100644
index 000000000..642c6d958
--- /dev/null
+++ b/apps/mobile/src/relative-date.ts
@@ -0,0 +1,20 @@
+/**
+ * Relative time for activity timestamps. Values slightly in the future are
+ * clock skew and still read "Just now"; further future values fall back to a
+ * date instead of claiming they just happened.
+ */
+export function relativeDate(value: string, now = Date.now()): string {
+  const parsed = Date.parse(value);
+  if (!Number.isFinite(parsed)) return value;
+  const diff = now - parsed;
+  if (diff < -60_000) return dayLabel(parsed);
+  const elapsed = Math.max(0, diff);
+  if (elapsed < 60_000) return "Just now";
+  if (elapsed < 3600_000) return `${Math.floor(elapsed / 60_000)}m ago`;
+  if (elapsed < 86400_000) return `${Math.floor(elapsed / 3600_000)}h ago`;
+  return dayLabel(parsed);
+}
+
+function dayLabel(value: number): string {
+  return new Date(value).toLocaleDateString("en-US", { month: "short", day: "numeric" });
+}
diff --git a/apps/mobile/src/ui.tsx b/apps/mobile/src/ui.tsx
index ce36605cb..0346f6478 100644
--- a/apps/mobile/src/ui.tsx
+++ b/apps/mobile/src/ui.tsx
@@ -446,16 +446,7 @@ export function timeLabel(value: string, timeZone?: string) {
     ? value
     : date.toLocaleTimeString("en-US", { hour: "numeric", minute: "2-digit", timeZone });
 }
-export function relativeDate(value: string) {
-  const diff = Date.now() - new Date(value).getTime();
-  return diff < 60_000
-    ? "Just now"
-    : diff < 3600_000
-      ? `${Math.floor(diff / 60_000)}m ago`
-      : diff < 86400_000
-        ? `${Math.floor(diff / 3600_000)}h ago`
-        : dateLabel(value);
-}
+export { relativeDate } from "./relative-date";
 
 export function resultSummary(value: string) {
   return /^Saved to (?:sample|local) sent mail(?: · .+)?$/.test(value)
diff --git a/apps/mobile/test/relative-date.test.ts b/apps/mobile/test/relative-date.test.ts
new file mode 100644
index 000000000..ab65f1210
--- /dev/null
+++ b/apps/mobile/test/relative-date.test.ts
@@ -0,0 +1,24 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { relativeDate } from "../src/relative-date.ts";
+
+const now = Date.parse("2026-09-30T12:00:00Z");
+
+test("recent past timestamps keep their buckets", () => {
+  assert.equal(relativeDate("2026-09-30T11:59:30Z", now), "Just now");
+  assert.equal(relativeDate("2026-09-30T11:30:00Z", now), "30m ago");
+  assert.equal(relativeDate("2026-09-30T09:00:00Z", now), "3h ago");
+});
+
+test("future timestamps beyond clock skew show a date instead of just now", () => {
+  assert.equal(relativeDate("2026-09-30T12:00:10Z", now), "Just now");
+  const expected = new Date(Date.parse("2026-10-05T12:00:00Z")).toLocaleDateString("en-US", {
+    month: "short",
+    day: "numeric",
+  });
+  assert.equal(relativeDate("2026-10-05T12:00:00Z", now), expected);
+});
+
+test("an unparseable timestamp is returned unchanged", () => {
+  assert.equal(relativeDate("not-a-date", now), "not-a-date");
+});