diff --git a/web/src/lib/utils/relativeTime.test.ts b/web/src/lib/utils/relativeTime.test.ts
new file mode 100644
index 00000000..05fc20da
--- /dev/null
+++ b/web/src/lib/utils/relativeTime.test.ts
@@ -0,0 +1,45 @@
+import { afterEach, describe, expect, test, vi } from 'vitest';
+import { relativeTime } from './relativeTime';
+
+// Fixed "now" so the thresholds are exercised deterministically rather than
+// against the wall clock, which would make the minute boundary flaky.
+const NOW = new Date('2026-08-16T12:00:00Z');
+
+function ago(ms: number): string {
+  return new Date(NOW.getTime() - ms).toISOString();
+}
+
+afterEach(() => vi.useRealTimers());
+
+describe('relativeTime', () => {
+  test.each([
+    ['under a minute', 30 * 1_000, 'just now'],
+    ['exactly a minute', 60 * 1_000, '1m ago'],
+    ['minutes', 42 * 60 * 1_000, '42m ago'],
+    ['exactly an hour', 3_600_000, '1h ago'],
+    ['hours', 5 * 3_600_000, '5h ago'],
+    ['exactly a day', 24 * 3_600_000, '1d ago'],
+    ['days', 9 * 24 * 3_600_000, '9d ago']
+  ])('%s', (_label, delta, expected) => {
+    vi.useFakeTimers();
+    vi.setSystemTime(NOW);
+    expect(relativeTime(ago(delta))).toBe(expected);
+  });
+
+  // The unit steps down at each boundary rather than compounding, so 25
+  // hours is "1d ago" and never "1d 1h ago".
+  test('reports only the largest whole unit', () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(NOW);
+    expect(relativeTime(ago(25 * 3_600_000))).toBe('1d ago');
+    expect(relativeTime(ago(90 * 60 * 1_000))).toBe('1h ago');
+  });
+
+  // A clock skewed behind the server produces a future timestamp; it must
+  // degrade to "just now" rather than rendering a negative age.
+  test('a future timestamp reads as just now', () => {
+    vi.useFakeTimers();
+    vi.setSystemTime(NOW);
+    expect(relativeTime(new Date(NOW.getTime() + 60_000).toISOString())).toBe('just now');
+  });
+});
diff --git a/web/src/lib/utils/relativeTime.ts b/web/src/lib/utils/relativeTime.ts
new file mode 100644
index 00000000..7ab3398a
--- /dev/null
+++ b/web/src/lib/utils/relativeTime.ts
@@ -0,0 +1,27 @@
+/**
+ * Coarse "how long ago" label for an ISO timestamp — "3d ago", "5h ago",
+ * "12m ago", or "just now" under a minute.
+ *
+ * The single source for the admin/triage surfaces, which had three
+ * byte-identical private copies of this before it was extracted (admin
+ * quarantine, admin playback-errors, library/hidden). Each showed the age
+ * of something an operator is deciding about, so they must read the same
+ * — a row that says "2d ago" on one screen and "2 days" on another makes
+ * the reader wonder whether they mean different things.
+ *
+ * Deliberately NOT the formatter used by listening history. HistoryRow
+ * shows a weekday and clock time for anything under a week ("Tue 21:40")
+ * because when you played something is more useful than how long ago,
+ * and it floors at "1m ago" rather than "just now". That is a different
+ * intent, not a copy that drifted, and it stays where it is.
+ */
+export function relativeTime(iso: string): string {
+  const ms = Date.now() - new Date(iso).getTime();
+  const days = Math.floor(ms / (24 * 3_600_000));
+  if (days >= 1) return `${days}d ago`;
+  const hours = Math.floor(ms / 3_600_000);
+  if (hours >= 1) return `${hours}h ago`;
+  const minutes = Math.floor(ms / 60_000);
+  if (minutes >= 1) return `${minutes}m ago`;
+  return 'just now';
+}
diff --git a/web/src/routes/admin/playback-errors/+page.svelte b/web/src/routes/admin/playback-errors/+page.svelte
index d43993f0..0008619a 100644
--- a/web/src/routes/admin/playback-errors/+page.svelte
+++ b/web/src/routes/admin/playback-errors/+page.svelte
@@ -13,6 +13,7 @@
   import { pushToast } from '$lib/stores/toast.svelte';
   import Modal from '$lib/components/Modal.svelte';
   import type { AdminPlaybackError, PlaybackErrorResolution } from '$lib/api/types';
+  import { relativeTime } from '$lib/utils/relativeTime';
 
   // Client-reported playback errors inbox. Two tabs — Unresolved
   // (default) / Resolved. Per-row: copy details to clipboard, delete
@@ -31,17 +32,6 @@
   const query = $derived($queryStore);
   const rows = $derived((query.data ?? []) as AdminPlaybackError[]);
 
-  function relativeTime(iso: string): string {
-    const ms = Date.now() - new Date(iso).getTime();
-    const days = Math.floor(ms / (24 * 3_600_000));
-    if (days >= 1) return `${days}d ago`;
-    const hours = Math.floor(ms / 3_600_000);
-    if (hours >= 1) return `${hours}h ago`;
-    const minutes = Math.floor(ms / 60_000);
-    if (minutes >= 1) return `${minutes}m ago`;
-    return 'just now';
-  }
-
   // Maps the kind enum to a short readable badge label.
   function kindLabel(kind: string): string {
     switch (kind) {
diff --git a/web/src/routes/admin/quarantine/+page.svelte b/web/src/routes/admin/quarantine/+page.svelte
index 9e5b148b..420274c9 100644
--- a/web/src/routes/admin/quarantine/+page.svelte
+++ b/web/src/routes/admin/quarantine/+page.svelte
@@ -16,6 +16,7 @@
   import { coverUrl } from '$lib/media/covers';
   import Modal from '$lib/components/Modal.svelte';
   import type { AdminQuarantineRow, LidarrQuarantineReason } from '$lib/api/types';
+  import { relativeTime } from '$lib/utils/relativeTime';
 
   // Aggregated triage queue. One row per track, with per-row resolution
   // actions: Resolve (clears reports), Delete file (Bronze; modal-confirm),
@@ -42,17 +43,6 @@
     other:      'Other'
   };
 
-  function relativeTime(iso: string): string {
-    const ms = Date.now() - new Date(iso).getTime();
-    const days = Math.floor(ms / (24 * 3_600_000));
-    if (days >= 1) return `${days}d ago`;
-    const hours = Math.floor(ms / 3_600_000);
-    if (hours >= 1) return `${hours}h ago`;
-    const minutes = Math.floor(ms / 60_000);
-    if (minutes >= 1) return `${minutes}m ago`;
-    return 'just now';
-  }
-
   // Row-level expand state: tracks which rows have their per-user report
   // details revealed. Keyed by track_id.
   let expanded = $state<Record<string, boolean>>({});
diff --git a/web/src/routes/library/hidden/+page.svelte b/web/src/routes/library/hidden/+page.svelte
index f9165925..3566e437 100644
--- a/web/src/routes/library/hidden/+page.svelte
+++ b/web/src/routes/library/hidden/+page.svelte
@@ -7,6 +7,7 @@
   import type { LidarrQuarantineMineRow, LidarrQuarantineReason } from '$lib/api/types';
   import ApiErrorBanner from '$lib/components/ApiErrorBanner.svelte';
   import { coverUrl } from '$lib/media/covers';
+  import { relativeTime } from '$lib/utils/relativeTime';
 
   const client = useQueryClient();
   const queryStore = createMyQuarantineQuery();
@@ -21,17 +22,6 @@
     other:      'Other'
   };
 
-  function relativeTime(iso: string): string {
-    const ms = Date.now() - new Date(iso).getTime();
-    const days = Math.floor(ms / (24 * 3_600_000));
-    if (days >= 1) return `${days}d ago`;
-    const hours = Math.floor(ms / 3_600_000);
-    if (hours >= 1) return `${hours}h ago`;
-    const minutes = Math.floor(ms / 60_000);
-    if (minutes >= 1) return `${minutes}m ago`;
-    return 'just now';
-  }
-
   async function onUnhide(trackID: string) {
     try {
       await unflagTrack(trackID);