diff --git a/README.md b/README.md
index 8f7ccfb..a382c18 100644
--- a/README.md
+++ b/README.md
@@ -17,6 +17,8 @@ export default {
       name: 'test',
       /** custom trust domains */
       domains: ['*.custom.com'],
+      /** optional, days before certificate expires */
+      ttlDays: 30,
       /** custom certification directory */
       certDir: '/Users/.../.devServer/cert',
     }),
diff --git a/src/certificate-expiration.ts b/src/certificate-expiration.ts
new file mode 100644
index 0000000..11cb0b6
--- /dev/null
+++ b/src/certificate-expiration.ts
@@ -0,0 +1,42 @@
+import { X509Certificate } from 'node:crypto'
+
+const MONTHS = [
+  'Jan',
+  'Feb',
+  'Mar',
+  'Apr',
+  'May',
+  'Jun',
+  'Jul',
+  'Aug',
+  'Sep',
+  'Oct',
+  'Nov',
+  'Dec',
+]
+
+export function isCertificateExpired(content: string): boolean {
+  const cert = new X509Certificate(content)
+  const expirationDate = getCertificateExpirationDate(cert)
+  return new Date() > expirationDate
+}
+
+function getCertificateExpirationDate(cert: X509Certificate): Date {
+  // validToDate is not available until node 22
+  if (cert.validToDate) {
+    return cert.validToDate
+  }
+
+  return parseNonStandardDateString(cert.validTo)
+}
+
+// validTo is a nonstandard format: %s %2d %02d:%02d:%02d %d%s GMT
+// https://github.com/nodejs/node/issues/52931
+export function parseNonStandardDateString(str: string): Date {
+  const [month, day, time, year] = str.split(' ').filter((part) => !!part)
+  // convert string month to number
+  const monthIndex = MONTHS.indexOf(month) + 1
+  return new Date(
+    `${year}-${monthIndex.toString().padStart(2, '0')}-${day.padStart(2, '0')}T${time}Z`,
+  )
+}
diff --git a/src/certificate.ts b/src/certificate.ts
index 22dbb53..74b9751 100644
--- a/src/certificate.ts
+++ b/src/certificate.ts
@@ -55,8 +55,8 @@ function toPositiveHex(hexString: string) {
 export function createCertificate(
   name: string = 'example.org',
   domains?: string[],
+  ttlDays = 30,
 ): string {
-  const days = 30
   const keySize = 2048
 
   const appendDomains = domains
@@ -146,7 +146,7 @@ export function createCertificate(
 
   cert.validity.notBefore = new Date()
   cert.validity.notAfter = new Date()
-  cert.validity.notAfter.setDate(cert.validity.notBefore.getDate() + days)
+  cert.validity.notAfter.setDate(cert.validity.notBefore.getDate() + ttlDays)
 
   cert.setSubject(attrs)
   cert.setIssuer(attrs)
diff --git a/src/index.ts b/src/index.ts
index 2b44c0c..1f93f1d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,6 +1,7 @@
 import path from 'node:path'
 import { promises as fsp } from 'node:fs'
 import type { Plugin } from 'vite'
+import { isCertificateExpired } from './certificate-expiration'
 
 const defaultCacheDir = 'node_modules/.vite'
 
@@ -8,6 +9,7 @@ interface Options {
   certDir: string
   domains: string[]
   name: string
+  ttlDays: number
 }
 
 function viteBasicSslPlugin(options?: Partial<Options>): Plugin {
@@ -18,6 +20,7 @@ function viteBasicSslPlugin(options?: Partial<Options>): Plugin {
         options?.certDir ?? (config.cacheDir ?? defaultCacheDir) + '/basic-ssl',
         options?.name,
         options?.domains,
+        options?.ttlDays,
       )
       const https = () => ({ cert: certificate, key: certificate })
       if (config.server.https === undefined || !!config.server.https) {
@@ -34,16 +37,15 @@ export async function getCertificate(
   cacheDir: string,
   name?: string,
   domains?: string[],
+  ttlDays?: number,
 ) {
   const cachePath = path.join(cacheDir, '_cert.pem')
 
   try {
-    const [stat, content] = await Promise.all([
-      fsp.stat(cachePath),
-      fsp.readFile(cachePath, 'utf8'),
-    ])
+    const content = await fsp.readFile(cachePath, 'utf8')
+    const isExpired = isCertificateExpired(content)
 
-    if (Date.now() - stat.ctime.valueOf() > 30 * 24 * 60 * 60 * 1000) {
+    if (isExpired) {
       throw new Error('cache is outdated.')
     }
 
@@ -52,6 +54,7 @@ export async function getCertificate(
     const content = (await import('./certificate')).createCertificate(
       name,
       domains,
+      ttlDays,
     )
     fsp
       .mkdir(cacheDir, { recursive: true })
diff --git a/test/test.spec.ts b/test/test.spec.ts
index 6637704..ab63a0e 100644
--- a/test/test.spec.ts
+++ b/test/test.spec.ts
@@ -1,5 +1,10 @@
-import { test, expect } from 'vitest'
+import { beforeEach, describe, test, expect, vi, Mock } from 'vitest'
+import { X509Certificate } from 'node:crypto'
 import { createCertificate } from '../src/certificate'
+import {
+  isCertificateExpired,
+  parseNonStandardDateString,
+} from '../src/certificate-expiration'
 
 test('create certificate', () => {
   const content = createCertificate()
@@ -10,3 +15,62 @@ test('create certificate', () => {
     /-----BEGIN CERTIFICATE-----(\n|\r|.)*-----END CERTIFICATE-----/,
   )
 })
+
+describe('isCertificateExpired', () => {
+  let validToDateMock: Mock
+  let validToMock: Mock
+
+  beforeEach(() => {
+    validToDateMock = vi.spyOn(X509Certificate.prototype, 'validToDate', 'get')
+    validToMock = vi.spyOn(X509Certificate.prototype, 'validTo', 'get')
+  })
+
+  describe('with validToDate', () => {
+    test('returns false', () => {
+      validToDateMock.mockReturnValue(new Date(Date.now() + 10000))
+
+      const content = createCertificate()
+      const isExpired = isCertificateExpired(content)
+      expect(isExpired).toBe(false)
+    })
+
+    test('returns true', () => {
+      validToDateMock.mockReturnValue(new Date(Date.now() - 10000))
+
+      const content = createCertificate()
+      const isExpired = isCertificateExpired(content)
+      expect(isExpired).toBe(true)
+    })
+  })
+
+  describe('with validTo', () => {
+    test('returns false', () => {
+      validToDateMock.mockReturnValue(undefined)
+      validToMock.mockReturnValue('Sep  3 21:40:37 2296 GMT')
+
+      const content = createCertificate()
+      const isExpired = isCertificateExpired(content)
+      expect(isExpired).toBe(false)
+    })
+
+    test('returns true', () => {
+      validToDateMock.mockReturnValue(undefined)
+      validToMock.mockReturnValue('Jan 22 08:20:44 2022 GMT')
+
+      const content = createCertificate()
+      const isExpired = isCertificateExpired(content)
+      expect(isExpired).toBe(true)
+    })
+  })
+})
+
+test('parseNonStandardDateString', () => {
+  const content = createCertificate()
+  const cert = new X509Certificate(content)
+  const date = parseNonStandardDateString(cert.validTo)
+  expect(date).toBeInstanceOf(Date)
+  expect(date.getTime()).toBeGreaterThan(0)
+  if (cert.validToDate) {
+    expect(date.getTime()).toBe(cert.validToDate.getTime())
+  }
+})
diff --git a/test/vitest.config.ts b/test/vitest.config.ts
index a013249..930e9d2 100644
--- a/test/vitest.config.ts
+++ b/test/vitest.config.ts
@@ -4,5 +4,6 @@ import { defineConfig } from 'vite'
 export default defineConfig({
   test: {
     testTimeout: 100000,
+    restoreMocks: true,
   },
 })