diff --git a/scripts/tray-check.mjs b/scripts/tray-check.mjs
index fc51ef7..1f8f5f5 100644
--- a/scripts/tray-check.mjs
+++ b/scripts/tray-check.mjs
@@ -156,6 +156,30 @@ try {
     check(now.status === 'idle' && !now.auto, 'a chosen Idle stays until Online is chosen', JSON.stringify(now))
     await tray('t.click(["Status", "Online"])')
     await waitFor('x.status === "online"', 'online again')
+
+    // The tray's number is the window's: it follows what is waiting, by the rail's rule.
+    const stage = (patch) => page.evaluate(`(() => { const s = window.__mohoShots.state(); const id = s.buffers.find((b) => b.kind === 'channel' && b.id.startsWith('checker')).id; window.__chan = id; window.__mohoShots.patch({ buffers: s.buffers.map((b) => (b.id === id ? { ...b, ...(${JSON.stringify(patch)}) } : b)) }); return id })()`)
+    const counted = async (want, what) => {
+      await until(main, `(() => { const s = globalThis.__mohoTray.state(); return s.mentions === ${want.mentions} && s.dms === ${want.dms} })()`, what)
+      check(true, what)
+    }
+    await tray('t.update({ unread: 0, dms: 0, mentions: 0 })')
+    const chan = await stage({ unread: 33, mentions: 2, highlight: true })
+    await counted({ mentions: 2, dms: 0 }, 'two mentions in a busy channel make the tray say two, not thirty-three')
+    check((await tray('t.state().latest')) === chan, 'and the menu opens that channel')
+    // Said the way another window would say it, through main.
+    const chanId = await page.evaluate('window.__chan')
+    await tray(`t.pref('mutedBuffers', [${JSON.stringify(chanId)}])`)
+    await counted({ mentions: 0, dms: 0 }, 'muting it takes it off the tray, as it does the rail')
+    await tray("t.pref('mutedBuffers', [])")
+    await counted({ mentions: 2, dms: 0 }, 'and unmuting puts it back')
+    await stage({ unread: 0, mentions: 0, highlight: false })
+    await counted({ mentions: 0, dms: 0 }, 'reading it somewhere else clears the tray as it clears the window')
+    await page.evaluate(`(() => { const s = window.__mohoShots.state(); window.__mohoShots.patch({ buffers: [...s.buffers, { id: 'checker@localhost|bobdm', accountId: s.accounts[0].id, kind: 'dm', name: 'bob', lastActivityTs: 1, unread: 3, highlight: false, mentions: 0 }] }); return true })()`)
+    await counted({ mentions: 0, dms: 3 }, 'a direct message counts for each unread message in it')
+    check(/3 direct messages/.test(await tray('t.tooltip()')), 'and the tooltip says so', await tray('t.tooltip()'))
+    await page.evaluate(`(() => { const s = window.__mohoShots.state(); window.__mohoShots.patch({ buffers: s.buffers.filter((b) => b.id !== 'checker@localhost|bobdm') }); return true })()`)
+    await counted({ mentions: 0, dms: 0 }, 'and the tray is empty again')
   } finally {
     irc.close()
   }
diff --git a/src/main/index.ts b/src/main/index.ts
index b025308..c4983b6 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -679,7 +679,7 @@ function refreshTrayMenu(): void {
     {
       toggleWindow,
       openLatest: () => {
-        const id = notifier.latestUnread()
+        const id = lastTray.latest ?? notifier.latestUnread()
         if (id) openConversation(id)
       },
       openSettings: () => tellWindow('settings'),
@@ -788,6 +788,14 @@ function wireIpc(): void {
 
   ipcMain.on(IPC.activity, () => idleWatcher.activity())
 
+  // What is waiting, as the window counts it. The tray's number is the window's
+  // own: counted here from notifications it drifted from what the window showed.
+  ipcMain.on(IPC.trayUnread, (_e, count: { dms: number; mentions: number; latest: string | null }) => {
+    const dms = Math.max(0, Number(count?.dms) || 0)
+    const mentions = Math.max(0, Number(count?.mentions) || 0)
+    updateTray({ unread: dms + mentions, dms, mentions, latest: typeof count?.latest === 'string' ? count.latest : null })
+  })
+
   ipcMain.handle(IPC.markBufferRead, (_e, bufferId: string) => notifier.clear(bufferId))
 
   // Every window draws its own title bar, so these act on whichever window
@@ -1260,7 +1268,8 @@ app.whenReady().then(() => {
 
   notifier = new Notifier(
     prefs,
-    updateTray,
+    // The tray's number is the window's, not this tally's - see IPC.trayUnread.
+    () => {},
     openConversation,
     () => mainWindow?.webContents ?? null,
     (bufferId) => popoutState().watched.includes(bufferId),
@@ -1320,6 +1329,8 @@ app.whenReady().then(() => {
       update: updateTray,
       idle: (v: boolean | null) => idleWatcher.forceForTesting(v),
       lastActivity: () => idleWatcher.lastActivityAt(),
+      state: () => lastTray,
+      pref: (key: string, value: unknown) => applyPref(key, value),
       icon: () => lastTrayIcon,
       tooltip: () => lastTrayTooltip,
       menu: () => lastTrayMenu,
diff --git a/src/main/tray.ts b/src/main/tray.ts
index 67ca8e5..c038c55 100644
--- a/src/main/tray.ts
+++ b/src/main/tray.ts
@@ -15,6 +15,8 @@ export interface TrayState {
   dms: number
   /** Of those, everything else: somebody mentioning this account in a channel. */
   mentions: number
+  /** The conversation the menu's first line opens, where the window has said. */
+  latest?: string | null
 }
 
 export const NOTHING_WAITING: TrayState = { unread: 0, dms: 0, mentions: 0 }
diff --git a/src/preload/index.ts b/src/preload/index.ts
index 43c2867..67a2b15 100644
--- a/src/preload/index.ts
+++ b/src/preload/index.ts
@@ -99,6 +99,11 @@ const api = {
     ipcRenderer.send(IPC.trayStatus, statuses, offered, shown, invisibleName)
   },
 
+  /** Says what is waiting, counted the way the rail counts it, for the tray's number. */
+  setTrayUnread(count: { dms: number; mentions: number; latest: string | null }): void {
+    ipcRenderer.send(IPC.trayUnread, count)
+  },
+
   onMaximizeChange(cb: (maximized: boolean) => void): () => void {
     const handler = (_e: unknown, v: boolean): void => cb(v)
     ipcRenderer.on(IPC.maximizeChanged, handler)
diff --git a/src/renderer/src/App.tsx b/src/renderer/src/App.tsx
index 7d3681f..dcdd8ff 100644
--- a/src/renderer/src/App.tsx
+++ b/src/renderer/src/App.tsx
@@ -8,6 +8,7 @@ import { MessageList } from './components/MessageList'
 import { MentionsInbox } from './components/MentionsInbox'
 import { MentionsPage } from './components/MentionsPage'
 import { INVITE_PREFIX, MENTIONS_GROUP_ID } from './lib/groups'
+import { trayCount } from './lib/traycount'
 import { Composer } from './components/Composer'
 import { MembershipGate } from './components/MembershipGate'
 import { NickList } from './components/NickList'
@@ -89,6 +90,22 @@ export default function App(): JSX.Element {
     else delete document.documentElement.dataset.reduceMotion
   }, [density, reduceMotion])
   const [userListFolded, setUserListFolded] = usePref<boolean>('ui.userListFolded', false)
+
+  // What the tray says is waiting, which is whatever the rail would add up to:
+  // the same rule, from the same lists, said to the main process whenever the
+  // answer changes. Told only when it has, since most changes to the buffers
+  // are not to what is waiting.
+  const [trayMuted] = usePref<string[]>('mutedBuffers', [])
+  const [trayHidden] = usePref<string[]>('hiddenBuffers', [])
+  const [trayMutedGroups] = usePref<string[]>('mutedGroups', [])
+  const lastTray = useRef('')
+  useEffect(() => {
+    const count = trayCount(allBuffers, trayMuted, trayHidden, trayMutedGroups)
+    const said = JSON.stringify(count)
+    if (said === lastTray.current) return
+    lastTray.current = said
+    window.moho.setTrayUnread(count)
+  }, [allBuffers, trayMuted, trayHidden, trayMutedGroups])
   const [savedBufferId] = usePref<string>('ui.activeBufferId', '')
   const [savedGroupId] = usePref<string>('ui.activeGroupId', '')
 
diff --git a/src/renderer/src/lib/traycount.test.ts b/src/renderer/src/lib/traycount.test.ts
new file mode 100644
index 0000000..83a8f83
--- /dev/null
+++ b/src/renderer/src/lib/traycount.test.ts
@@ -0,0 +1,36 @@
+import { describe, expect, it } from 'vitest'
+import { trayCount } from './traycount'
+import type { BufferEntry } from '../state/store'
+
+const buf = (over: Partial<BufferEntry>): BufferEntry =>
+  ({ id: 'a|#x', accountId: 'a', kind: 'channel', name: '#x', lastActivityTs: 0, groupId: 'g', unread: 0, highlight: false, mentions: 0, ...over }) as BufferEntry
+
+describe('the number on the tray', () => {
+  it('is nothing when nothing is waiting', () => {
+    expect(trayCount([buf({}), buf({ id: 'a|#y', unread: 40 })], [], [], [])).toEqual({ dms: 0, mentions: 0, latest: null })
+  })
+
+  it('counts a channel by its mentions and not by its messages', () => {
+    expect(trayCount([buf({ unread: 33, mentions: 2, highlight: true })], [], [], [])).toEqual({ dms: 0, mentions: 2, latest: 'a|#x' })
+  })
+
+  it('counts a direct message by each unread message in it', () => {
+    expect(trayCount([buf({ id: 'a|bob', kind: 'dm', unread: 3 })], [], [], [])).toEqual({ dms: 3, mentions: 0, latest: 'a|bob' })
+  })
+
+  it('does not count what is muted or hidden, mentions included', () => {
+    const rows = [buf({ id: 'a|#m', mentions: 4 }), buf({ id: 'a|#h', mentions: 5 }), buf({ id: 'a|gm', mentions: 6, groupId: 'muted-group' })]
+    expect(trayCount(rows, ['a|#m'], ['a|#h'], ['muted-group'])).toEqual({ dms: 0, mentions: 0, latest: null })
+    expect(trayCount([buf({ mentions: 2, serverMuted: true })], [], [], [])).toEqual({ dms: 0, mentions: 0, latest: null })
+  })
+
+  it('names the most recently active conversation that has something, for the tray to open', () => {
+    const rows = [buf({ id: 'a|old', mentions: 1, lastActivityTs: 10 }), buf({ id: 'a|new', mentions: 1, lastActivityTs: 20 }), buf({ id: 'a|quiet', lastActivityTs: 99 })]
+    expect(trayCount(rows, [], [], []).latest).toBe('a|new')
+  })
+
+  it('adds the two kinds together and keeps them apart', () => {
+    const rows = [buf({ id: 'a|bob', kind: 'dm', unread: 2 }), buf({ mentions: 3 })]
+    expect(trayCount(rows, [], [], [])).toMatchObject({ dms: 2, mentions: 3 })
+  })
+})
diff --git a/src/renderer/src/lib/traycount.ts b/src/renderer/src/lib/traycount.ts
new file mode 100644
index 0000000..89547c9
--- /dev/null
+++ b/src/renderer/src/lib/traycount.ts
@@ -0,0 +1,42 @@
+import { countsTowardRail, isDirectMessage } from './groups'
+import type { BufferEntry } from '../state/store'
+
+/** What the tray is told is waiting. */
+export interface TrayCount {
+  /** Unread direct messages, counted by the message. */
+  dms: number
+  /** Mentions in everywhere that is not a direct message, counted by the mention. */
+  mentions: number
+  /** The conversation to open from the tray: the most recently active one with something counted. */
+  latest: string | null
+}
+
+/**
+ * The number on the tray, worked out the way the rail's is.
+ *
+ * The tray used to keep a count of its own in the main process, from the
+ * notifications it was sent and a handful of "this was read" messages, and the
+ * two drifted: a read on another device cleared the window and not the tray, a
+ * mention in the conversation already open raised the tray and was never
+ * counted by the window, and a room muted afterwards stayed in the tray's
+ * number. It also counted conversations where the rail counts messages.
+ *
+ * So the window - which already knows every one of those things, because it is
+ * what draws them - says what is waiting, by the same rule as the rail: a
+ * muted or hidden conversation does not count, a direct message counts for each
+ * unread message in it, and anywhere else counts for its mentions.
+ */
+export function trayCount(buffers: BufferEntry[], muted: string[], hidden: string[], mutedGroups: string[]): TrayCount {
+  let dms = 0
+  let mentions = 0
+  let latest: BufferEntry | null = null
+  for (const b of buffers) {
+    if (!countsTowardRail(b, muted, hidden, mutedGroups)) continue
+    const waiting = isDirectMessage(b) ? b.unread : b.mentions
+    if (waiting <= 0) continue
+    if (isDirectMessage(b)) dms += waiting
+    else mentions += waiting
+    if (!latest || b.lastActivityTs > latest.lastActivityTs) latest = b
+  }
+  return { dms, mentions, latest: latest?.id ?? null }
+}
diff --git a/src/shared/ipc.ts b/src/shared/ipc.ts
index 05f3039..e5b1790 100644
--- a/src/shared/ipc.ts
+++ b/src/shared/ipc.ts
@@ -57,6 +57,8 @@ export const IPC = {
   trayCommand: 'moho:tray:command',
   /** window -> main: the status each connected account is at. */
   trayStatus: 'moho:tray:status',
+  /** window -> main: what is waiting, for the number on the tray. */
+  trayUnread: 'moho:tray:unread',
   /** window -> main: something was used in this window, so the person is here. */
   activity: 'moho:activity'
 } as const