diff --git a/frontend/src/components/payment/PaymentQRDialog.vue b/frontend/src/components/payment/PaymentQRDialog.vue
index 7dff831a6a..621d8f010d 100644
--- a/frontend/src/components/payment/PaymentQRDialog.vue
+++ b/frontend/src/components/payment/PaymentQRDialog.vue
@@ -234,12 +234,13 @@ async function tryRecoverPendingOrder(order: PaymentOrder): Promise<PaymentOrder
 
 function startCountdown(seconds: number) {
   remainingSeconds.value = Math.max(0, seconds)
+  const deadline = Date.now() + remainingSeconds.value * 1000
   if (remainingSeconds.value <= 0) {
     expired.value = true
     return
   }
   countdownTimer = setInterval(() => {
-    remainingSeconds.value--
+    remainingSeconds.value = Math.max(0, Math.floor((deadline - Date.now()) / 1000))
     if (remainingSeconds.value <= 0) {
       expired.value = true
       cleanup()
diff --git a/frontend/src/components/payment/PaymentStatusPanel.vue b/frontend/src/components/payment/PaymentStatusPanel.vue
index e751c42225..243ffac768 100644
--- a/frontend/src/components/payment/PaymentStatusPanel.vue
+++ b/frontend/src/components/payment/PaymentStatusPanel.vue
@@ -450,9 +450,10 @@ async function pollStatus() {
 
 function startCountdown(seconds: number) {
   remainingSeconds.value = Math.max(0, seconds)
+  const deadline = Date.now() + remainingSeconds.value * 1000
   if (remainingSeconds.value <= 0) { setOutcome('expired'); return }
   countdownTimer = setInterval(() => {
-    remainingSeconds.value--
+    remainingSeconds.value = Math.max(0, Math.floor((deadline - Date.now()) / 1000))
     if (remainingSeconds.value <= 0) { setOutcome('expired'); cleanup() }
   }, 1000)
 }
diff --git a/frontend/src/components/payment/__tests__/paymentCountdown.spec.ts b/frontend/src/components/payment/__tests__/paymentCountdown.spec.ts
new file mode 100644
index 0000000000..fec3892474
--- /dev/null
+++ b/frontend/src/components/payment/__tests__/paymentCountdown.spec.ts
@@ -0,0 +1,68 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import { enableAutoUnmount, mount } from '@vue/test-utils'
+import PaymentQRDialog from '../PaymentQRDialog.vue'
+import PaymentStatusPanel from '../PaymentStatusPanel.vue'
+import PaymentQRCodeView from '@/views/user/PaymentQRCodeView.vue'
+
+vi.mock('vue-i18n', async (importOriginal) => ({
+  ...await importOriginal<typeof import('vue-i18n')>(),
+  useI18n: () => ({ t: (key: string) => key }),
+}))
+vi.mock('@/components/layout/AppLayout.vue', () => ({
+  default: { template: '<div><slot /></div>' },
+}))
+vi.mock('@/stores/payment', () => ({
+  usePaymentStore: () => ({ pollOrderStatus: vi.fn().mockResolvedValue(null) }),
+}))
+vi.mock('@/stores', () => ({ useAppStore: () => ({ showError: vi.fn() }) }))
+vi.mock('@/api/payment', () => ({ paymentAPI: {} }))
+vi.mock('qrcode', () => ({ default: { toCanvas: vi.fn() } }))
+vi.mock('vue-router', () => ({
+  useRoute: () => ({ query: { order_id: '42', expires_at: new Date(Date.now() + 120_000).toISOString() } }),
+  useRouter: () => ({ push: vi.fn() }),
+}))
+
+enableAutoUnmount(afterEach)
+beforeEach(() => {
+  vi.useFakeTimers()
+  vi.setSystemTime(new Date('2026-09-30T12:00:00Z'))
+})
+afterEach(() => vi.useRealTimers())
+
+async function open(kind: 'dialog' | 'panel' | 'page') {
+  const props = { orderId: 42, qrCode: '', expiresAt: new Date(Date.now() + 120_000).toISOString(), paymentType: 'custom' }
+  const global = { stubs: {
+    Icon: true,
+    AppLayout: { template: '<div><slot /></div>' },
+    BaseDialog: { props: ['show'], template: '<div v-if="show"><slot /><slot name="footer" /></div>' },
+  } }
+  if (kind === 'page') return mount(PaymentQRCodeView, { global })
+  if (kind === 'panel') return mount(PaymentStatusPanel, { props, global })
+  const wrapper = mount(PaymentQRDialog, { props: { ...props, show: false }, global })
+  await wrapper.setProps({ show: true })
+  return wrapper
+}
+
+describe.each(['dialog', 'panel', 'page'] as const)('payment countdown: %s', (kind) => {
+  it('catches up after timers were suspended', async () => {
+    const wrapper = await open(kind)
+    expect(wrapper.text()).toContain('02:00')
+    vi.setSystemTime(Date.now() + 65_000)
+    await vi.advanceTimersByTimeAsync(1000)
+    expect(wrapper.text()).toContain('00:54')
+  })
+
+  it('expires and stops polling on the first overdue tick', async () => {
+    const wrapper = await open(kind)
+    vi.setSystemTime(Date.now() + 121_000)
+    await vi.advanceTimersByTimeAsync(1000)
+    expect(wrapper.text()).toContain('payment.qr.expired')
+    expect(vi.getTimerCount()).toBe(0)
+  })
+
+  it('still counts down normally', async () => {
+    const wrapper = await open(kind)
+    await vi.advanceTimersByTimeAsync(1000)
+    expect(wrapper.text()).toContain('01:59')
+  })
+})
diff --git a/frontend/src/views/user/PaymentQRCodeView.vue b/frontend/src/views/user/PaymentQRCodeView.vue
index 0569bf6907..b535b14682 100644
--- a/frontend/src/views/user/PaymentQRCodeView.vue
+++ b/frontend/src/views/user/PaymentQRCodeView.vue
@@ -157,12 +157,13 @@ async function pollStatus() {
 
 function startCountdown(seconds: number) {
   remainingSeconds.value = Math.max(0, seconds)
+  const deadline = Date.now() + remainingSeconds.value * 1000
   if (remainingSeconds.value <= 0) {
     expired.value = true
     return
   }
   countdownTimer = setInterval(() => {
-    remainingSeconds.value--
+    remainingSeconds.value = Math.max(0, Math.floor((deadline - Date.now()) / 1000))
     if (remainingSeconds.value <= 0) {
       expired.value = true
       cleanup()