diff --git a/Readme.md b/Readme.md
index 25621c1..074cb0c 100644
--- a/Readme.md
+++ b/Readme.md
@@ -70,9 +70,9 @@ app.use(async (ctx, next) => {
 // next is a function that is invoked to execute the downstream middleware. It returns a Promise with a then function for running code after completion.
 
 app.use((ctx, next) => {
-  const start = new Date();
+  const start = Date.now();
   return next().then(() => {
-    const ms = new Date() - start;
+    const ms = Date.now() - start;
     console.log(`${ctx.method} ${ctx.url} - ${ms}ms`);
   });
 });
diff --git a/docs/api/index.md b/docs/api/index.md
index a2a23a0..a25da8c 100644
--- a/docs/api/index.md
+++ b/docs/api/index.md
@@ -81,18 +81,18 @@ const app = new Koa();
 // x-response-time
 
 app.use(async function (ctx, next) {
-  const start = new Date();
+  const start = Date.now();
   await next();
-  const ms = new Date() - start;
+  const ms = Date.now() - start;
   ctx.set('X-Response-Time', `${ms}ms`);
 });
 
 // logger
 
 app.use(async function (ctx, next) {
-  const start = new Date();
+  const start = Date.now();
   await next();
-  const ms = new Date() - start;
+  const ms = Date.now() - start;
   console.log(`${ctx.method} ${ctx.url} - ${ms}`);
 });
 
diff --git a/docs/guide.md b/docs/guide.md
index c2ee87b..de27ade 100644
--- a/docs/guide.md
+++ b/docs/guide.md
@@ -13,9 +13,9 @@
 
 ```js
 async function responseTime(ctx, next) {
-  const start = new Date();
+  const start = Date.now();
   await next();
-  const ms = new Date() - start;
+  const ms = Date.now() - start;
   ctx.set('X-Response-Time', `${ms}ms`);
 }
 
diff --git a/docs/migration.md b/docs/migration.md
index 172d877..d6ed25d 100644
--- a/docs/migration.md
+++ b/docs/migration.md
@@ -39,9 +39,9 @@ It is however recommended that you choose to migrate all v1.x middleware as soon
 ```js
 // Koa will convert
 app.use(function *(next) {
-  const start = new Date();
+  const start = Date.now();
   yield next;
-  const ms = new Date() - start;
+  const ms = Date.now() - start;
   console.log(`${this.method} ${this.url} - ${ms}ms`);
 });
 ```
@@ -52,9 +52,9 @@ You could do it manually as well, in which case Koa will not convert.
 const convert = require('koa-convert');
 
 app.use(convert(function *(next) {
-  const start = new Date();
+  const start = Date.now();
   yield next;
-  const ms = new Date() - start;
+  const ms = Date.now() - start;
   console.log(`${this.method} ${this.url} - ${ms}ms`);
 }));
 ```