diff --git a/README.md b/README.md
index 36481fb..1889c7d 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@ This middleware guarantees the following:
   - If a session has not been updated within `maxAge`, its data will be expired.
 - Minimum public interfaces and configuration options.
   - Cookie options: `maxAge`, `path`, `domain`, `secure`, `httpOnly`
-  - Session interfaces: `session`, `sessionHandler { regenerateId(), setMaxAge() }`
+  - Session interfaces: `session`, `sessionHandler { regenerateId() }`
   - Store interfaces: `get()`, `set()`, `destroy()`
 
 
@@ -66,14 +66,13 @@ app.listen(3000)
 - session data via `ctx.session` (the same way as `koa-generic-session`)
 - session methods via `ctx.sessionHandler`
   - `regenerateId()`: regenerate session id
-  - `setMaxAge(ms)`: update session's `maxAge` to `ms` milliseconds, only take effect when session data has been changed
 
 
 ## Options
 
 - `key`: session cookie name and store key prefix
 - `store`: session store
-- `cookie`: cookie options, only supports `maxAge`, `path`, `domain`, `secure`, `httpOnly` (see option details in [`cookies`](https://github.com/pillarjs/cookies) module)
+- `cookie`: cookie options, can be an object (static cookie options) or a function that returns an object (dynamic cookie options). Only `maxAge`, `path`, `domain`, `secure`, `httpOnly` are supported as option keys (see option details in [`cookies`](https://github.com/pillarjs/cookies) module).
 
 
 ## Session expiration
@@ -84,7 +83,17 @@ Default session has settings `cookie.maxAge = 0` for cookie and `ttl = ONE_DAY`
 
 With settings that `cookie.maxAge > 0`, the `ttl` for store data will be always the same as `maxAge`.
 
-When a middleware updates session data, it can also update the `maxAge` by calling `sessionHandler.setMaxAge(ms)`. Then the session's expiration time will be updated to `now() + maxAge` milliseconds.
+When setting `cookie` option to a plain object, all sessions will use the same cookie options. If a function is assigned to `cookie`, cookie options will be dynamically calculated at each (non-empty) session's saving stage.
+You may use different `maxAge` for user and guest sessions, by initializing the session middleware as below:
+```javascript
+session({
+  cookie: ctx => {
+    return {
+      maxAge: ctx.session.user ? ONE_MONTH : ONE_DAY,
+    }
+  }
+})
+```
 
 
 ## Session security
diff --git a/package.json b/package.json
index 75757da..0d69497 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "koa-session-minimal",
-  "version": "2.0.1",
+  "version": "3.0.0",
   "description": "Minimal implementation of session middleware for Koa 2. Inspired by and compatible with koa-generic-session",
   "main": "dist/session.js",
   "scripts": {
diff --git a/src/session.js b/src/session.js
index da67915..34d4c39 100644
--- a/src/session.js
+++ b/src/session.js
@@ -5,6 +5,20 @@ const MemoryStore = require('./memory_store')
 
 const ONE_DAY = 24 * 3600 * 1000 // one day in milliseconds
 
+const cookieOpt = cookie => {
+  const options = Object.assign({
+    maxAge: 0, // default to use session cookie
+    path: '/',
+    secure: false,
+    httpOnly: true,
+  }, cookie || {}, {
+    overwrite: true, // overwrite previous session cookie changes
+    signed: false, // disable signed option
+  })
+  if (!(options.maxAge >= 0)) options.maxAge = 0
+  return options
+}
+
 const deleteSession = (ctx, key, cookie, store, sid) => {
   const deleteOption = Object.assign({}, cookie)
   delete deleteOption.maxAge
@@ -22,20 +36,9 @@ module.exports = options => {
   const opt = options || {}
   const key = opt.key || 'koa:sess'
   const store = new Store(opt.store || new MemoryStore())
-  const defaultCookie = Object.assign({
-    maxAge: 0, // default to use session cookie
-    path: '/',
-    secure: false,
-    httpOnly: true,
-  }, opt.cookie || {}, {
-    overwrite: true, // overwrite previous session cookie changes
-    signed: false, // disable signed option
-  })
-  if (!(defaultCookie.maxAge >= 0)) defaultCookie.maxAge = 0
+  const defaultCookie = opt.cookie instanceof Function ? opt.cookie : cookieOpt(opt.cookie)
 
   return async (ctx, next) => {
-    const cookie = Object.assign({}, defaultCookie)
-
     // initialize session id and data
     const cookieSid = ctx.cookies.get(key)
 
@@ -57,13 +60,11 @@ module.exports = options => {
       regenerateId: () => {
         sid = uid.sync(24)
       },
-      setMaxAge: ms => {
-        cookie.maxAge = ms >= 0 ? ms : 0
-      },
     }
 
     await next()
 
+    const cookie = defaultCookie instanceof Function ? cookieOpt(defaultCookie(ctx)) : defaultCookie
     const sessionHasData = ctx.session && Object.keys(ctx.session).length
 
     if (sid !== cookieSid) { // a new session id
diff --git a/test/async_store.test.js b/test/async_store.test.js
index 4cfc253..93cf3d4 100644
--- a/test/async_store.test.js
+++ b/test/async_store.test.js
@@ -23,8 +23,7 @@ const updateSession = (ctx, next) => {
       break
     default:
       if (ctx.url.startsWith('/maxage/')) {
-        const ms = parseInt(ctx.url.replace('/maxage/', ''), 10)
-        ctx.sessionHandler.setMaxAge(ms)
+        ctx.ms = parseInt(ctx.url.replace('/maxage/', ''), 10)
         ctx.session.time = Date.now()
       }
   }
@@ -399,6 +398,33 @@ describe('session with async store', () => {
         })
     })
   })
+})
+
+describe('async store with dynamic cookie options', () => {
+  const app = new Koa()
+  const key = 'koa:sess'
+  const store = new SpyStore()
+
+  app.use(session({
+    store,
+    cookie: ctx => { // eslint-disable-line arrow-body-style
+      return {
+        maxAge: ctx.ms,
+      }
+    },
+  }))
+  app.use(updateSession)
+  app.use(sessionToBody)
+
+  const client = request(app.listen())
+  let startTime
+  let ttl
+
+  beforeEach(() => {
+    store.clear()
+    ttl = 24 * 3600 * 1000 // one day in milliseconds
+    startTime = Date.now()
+  })
 
   it('setMaxAge(ms) should set maxAge and ttl', done => {
     client.get('/maxage/0').expect(200).end((err1, res1) => {
@@ -413,7 +439,7 @@ describe('session with async store', () => {
         destroy: [],
       })
 
-      const maxAge = 1000
+      const maxAge = 123
       client.get(`/maxage/${maxAge}`).expect(200).end((err2, res2) => {
         if (err2) done(err2)
         validateCookie(res2, key)
diff --git a/test/generator_store.test.js b/test/generator_store.test.js
index a369fc7..ee15b82 100644
--- a/test/generator_store.test.js
+++ b/test/generator_store.test.js
@@ -23,8 +23,7 @@ const updateSession = (ctx, next) => {
       break
     default:
       if (ctx.url.startsWith('/maxage/')) {
-        const ms = parseInt(ctx.url.replace('/maxage/', ''), 10)
-        ctx.sessionHandler.setMaxAge(ms)
+        ctx.ms = parseInt(ctx.url.replace('/maxage/', ''), 10)
         ctx.session.time = Date.now()
       }
   }
@@ -399,6 +398,33 @@ describe('session with generator store', () => {
         })
     })
   })
+})
+
+describe('generator store with dynamic cookie options', () => {
+  const app = new Koa()
+  const key = 'koa:sess'
+  const store = new SpyStore()
+
+  app.use(session({
+    store,
+    cookie: ctx => { // eslint-disable-line arrow-body-style
+      return {
+        maxAge: ctx.ms,
+      }
+    },
+  }))
+  app.use(updateSession)
+  app.use(sessionToBody)
+
+  const client = request(app.listen())
+  let startTime
+  let ttl
+
+  beforeEach(() => {
+    store.clear()
+    ttl = 24 * 3600 * 1000 // one day in milliseconds
+    startTime = Date.now()
+  })
 
   it('setMaxAge(ms) should set maxAge and ttl', done => {
     client.get('/maxage/0').expect(200).end((err1, res1) => {
@@ -413,7 +439,7 @@ describe('session with generator store', () => {
         destroy: [],
       })
 
-      const maxAge = 1000
+      const maxAge = 123
       client.get(`/maxage/${maxAge}`).expect(200).end((err2, res2) => {
         if (err2) done(err2)
         validateCookie(res2, key)