diff --git a/docs/en/API-reference.md b/docs/en/API-reference.md
index a95bfe18f..1035b8773 100644
--- a/docs/en/API-reference.md
+++ b/docs/en/API-reference.md
@@ -492,3 +492,9 @@ plugin [`ToObject`](./Plugin.md#toobject)
 `.min` `.max` to compare given dayjs instances
 
 plugin [`MinMax`](./Plugin.md#minmax)
+
+### Calendar
+
+`.calendar` to display calendar time
+
+plugin [`Calendar`](./Plugin.md#calendar)
diff --git a/docs/en/Plugin.md b/docs/en/Plugin.md
index 3df237257..5fc968750 100644
--- a/docs/en/Plugin.md
+++ b/docs/en/Plugin.md
@@ -401,6 +401,26 @@ dayjs.max(dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01'))
 dayjs.min([dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01')])
 ```
 
+### Calendar
+
+- Calendar adds `.calendar` API to return a `string` to display calendar time
+
+```javascript
+import calendar from 'dayjs/plugin/calendar'
+
+dayjs.extend(calendar)
+
+dayjs().calendar(dayjs('2008-01-01'))
+dayjs().calendar(null, {
+  sameDay: '[Today at] h:mm A', // The same day ( Today at 2:30 AM )
+  nextDay: '[Tomorrow]', // The next day ( Tomorrow at 2:30 AM )
+  nextWeek: 'dddd', // The next week ( Sunday at 2:30 AM )
+  lastDay: '[Yesterday]', // The day before ( Yesterday at 2:30 AM )
+  lastWeek: '[Last] dddd', // Last week ( Last Monday at 2:30 AM )
+  sameElse: 'DD/MM/YYYY' // Everything else ( 7/10/2011 )
+})
+```
+
 ## Customize
 
 You could build your own Day.js plugin to meet different needs.
diff --git a/docs/es-es/API-reference.md b/docs/es-es/API-reference.md
index 8d3b1a31e..cde19d343 100644
--- a/docs/es-es/API-reference.md
+++ b/docs/es-es/API-reference.md
@@ -492,3 +492,9 @@ plugin [`ToObject`](./Plugin.md#toobject)
 `.min` `.max` to compare given dayjs instances.
 
 plugin [`MinMax`](./Plugin.md#minmax)
+
+### Calendar
+
+`.calendar` to display calendar time
+
+plugin [`Calendar`](./Plugin.md#calendar)
diff --git a/docs/es-es/Plugin.md b/docs/es-es/Plugin.md
index 279c5c85c..1b5362afd 100644
--- a/docs/es-es/Plugin.md
+++ b/docs/es-es/Plugin.md
@@ -401,6 +401,26 @@ dayjs.max(dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01'))
 dayjs.min([dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01')])
 ```
 
+### Calendar
+
+- Calendar adds `.calendar` API to return a `string` to display calendar time
+
+```javascript
+import calendar from 'dayjs/plugin/calendar'
+
+dayjs.extend(calendar)
+
+dayjs().calendar(dayjs('2008-01-01'))
+dayjs().calendar(null, {
+  sameDay: '[Today at] h:mm A', // The same day ( Today at 2:30 AM )
+  nextDay: '[Tomorrow]', // The next day ( Tomorrow at 2:30 AM )
+  nextWeek: 'dddd', // The next week ( Sunday at 2:30 AM )
+  lastDay: '[Yesterday]', // The day before ( Yesterday at 2:30 AM )
+  lastWeek: '[Last] dddd', // Last week ( Last Monday at 2:30 AM )
+  sameElse: 'DD/MM/YYYY' // Everything else ( 7/10/2011 )
+})
+```
+
 ## Personalización
 
 Puedes construir tu propio complemento de Day.js para cubrir tus necesidades.
diff --git a/docs/ja/API-reference.md b/docs/ja/API-reference.md
index 37fbcf409..d703fe3cc 100644
--- a/docs/ja/API-reference.md
+++ b/docs/ja/API-reference.md
@@ -548,3 +548,9 @@ plugin [`ToObject`](./Plugin.md#toobject)
 `.min` `.max` to compare given dayjs instances.
 
 plugin [`MinMax`](./Plugin.md#minmax)
+
+### Calendar
+
+`.calendar` to display calendar time
+
+plugin [`Calendar`](./Plugin.md#calendar)
diff --git a/docs/ja/Plugin.md b/docs/ja/Plugin.md
index d29c57f63..2daa02cb0 100644
--- a/docs/ja/Plugin.md
+++ b/docs/ja/Plugin.md
@@ -410,6 +410,26 @@ dayjs.max(dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01'))
 dayjs.min([dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01')])
 ```
 
+### Calendar
+
+- Calendar adds `.calendar` API to return a `string` to display calendar time
+
+```javascript
+import calendar from 'dayjs/plugin/calendar'
+
+dayjs.extend(calendar)
+
+dayjs().calendar(dayjs('2008-01-01'))
+dayjs().calendar(null, {
+  sameDay: '[Today at] h:mm A', // The same day ( Today at 2:30 AM )
+  nextDay: '[Tomorrow]', // The next day ( Tomorrow at 2:30 AM )
+  nextWeek: 'dddd', // The next week ( Sunday at 2:30 AM )
+  lastDay: '[Yesterday]', // The day before ( Yesterday at 2:30 AM )
+  lastWeek: '[Last] dddd', // Last week ( Last Monday at 2:30 AM )
+  sameElse: 'DD/MM/YYYY' // Everything else ( 7/10/2011 )
+})
+```
+
 ## カスタマイズ
 
 さまざまなニーズに合わせて独自の Day.js プラグインを構築することができます。
diff --git a/docs/ko/API-reference.md b/docs/ko/API-reference.md
index a5f40ef0a..10be81e2e 100644
--- a/docs/ko/API-reference.md
+++ b/docs/ko/API-reference.md
@@ -491,3 +491,9 @@ plugin [`ToObject`](./Plugin.md#toobject)
 `.min` `.max` to compare given dayjs instances.
 
 plugin [`MinMax`](./Plugin.md#minmax)
+
+### Calendar
+
+`.calendar` to display calendar time
+
+plugin [`Calendar`](./Plugin.md#calendar)
diff --git a/docs/ko/Plugin.md b/docs/ko/Plugin.md
index 91a705870..25c706221 100644
--- a/docs/ko/Plugin.md
+++ b/docs/ko/Plugin.md
@@ -402,6 +402,26 @@ dayjs.max(dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01'))
 dayjs.min([dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01')])
 ```
 
+### Calendar
+
+- Calendar adds `.calendar` API to return a `string` to display calendar time
+
+```javascript
+import calendar from 'dayjs/plugin/calendar'
+
+dayjs.extend(calendar)
+
+dayjs().calendar(dayjs('2008-01-01'))
+dayjs().calendar(null, {
+  sameDay: '[Today at] h:mm A', // The same day ( Today at 2:30 AM )
+  nextDay: '[Tomorrow]', // The next day ( Tomorrow at 2:30 AM )
+  nextWeek: 'dddd', // The next week ( Sunday at 2:30 AM )
+  lastDay: '[Yesterday]', // The day before ( Yesterday at 2:30 AM )
+  lastWeek: '[Last] dddd', // Last week ( Last Monday at 2:30 AM )
+  sameElse: 'DD/MM/YYYY' // Everything else ( 7/10/2011 )
+})
+```
+
 ## Customize
 
 다양한 요구를 충족하기위해 자신만의 Day.js 플러그인을 만들 수 있습니다.
diff --git a/docs/pt-br/API-reference.md b/docs/pt-br/API-reference.md
index d14c7958d..5a7009ef5 100644
--- a/docs/pt-br/API-reference.md
+++ b/docs/pt-br/API-reference.md
@@ -490,3 +490,9 @@ plugin [`ToObject`](./Plugin.md#toobject)
 `.min` `.max` to compare given dayjs instances.
 
 plugin [`MinMax`](./Plugin.md#minmax)
+
+### Calendar
+
+`.calendar` to display calendar time
+
+plugin [`Calendar`](./Plugin.md#calendar)
diff --git a/docs/pt-br/Plugin.md b/docs/pt-br/Plugin.md
index dfcb55499..676cff560 100644
--- a/docs/pt-br/Plugin.md
+++ b/docs/pt-br/Plugin.md
@@ -401,6 +401,26 @@ dayjs.max(dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01'))
 dayjs.min([dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01')])
 ```
 
+### Calendar
+
+- Calendar adds `.calendar` API to return a `string` to display calendar time
+
+```javascript
+import calendar from 'dayjs/plugin/calendar'
+
+dayjs.extend(calendar)
+
+dayjs().calendar(dayjs('2008-01-01'))
+dayjs().calendar(null, {
+  sameDay: '[Today at] h:mm A', // The same day ( Today at 2:30 AM )
+  nextDay: '[Tomorrow]', // The next day ( Tomorrow at 2:30 AM )
+  nextWeek: 'dddd', // The next week ( Sunday at 2:30 AM )
+  lastDay: '[Yesterday]', // The day before ( Yesterday at 2:30 AM )
+  lastWeek: '[Last] dddd', // Last week ( Last Monday at 2:30 AM )
+  sameElse: 'DD/MM/YYYY' // Everything else ( 7/10/2011 )
+})
+```
+
 ## Customizar
 
 Você também pode construir seu próprio plugin Day.js para diferentes necessidades.
diff --git a/docs/zh-cn/API-reference.md b/docs/zh-cn/API-reference.md
index 75c7a3d0a..4c0c4e5fd 100644
--- a/docs/zh-cn/API-reference.md
+++ b/docs/zh-cn/API-reference.md
@@ -543,3 +543,9 @@ plugin [`IsoWeeksInYear`](./Plugin.md#isoweeksinyear)
 `.min` `.max` 比较传入的 dayjs 实例的大小
 
 plugin [`MinMax`](./Plugin.md#minmax)
+
+### 日历时间
+
+`.calendar` 来显示日历时间
+
+plugin [`Calendar`](./Plugin.md#calendar)
diff --git a/docs/zh-cn/Plugin.md b/docs/zh-cn/Plugin.md
index 49b0a65ab..89caccc6b 100644
--- a/docs/zh-cn/Plugin.md
+++ b/docs/zh-cn/Plugin.md
@@ -389,7 +389,7 @@ dayjs('2019-01-25').toObject()
 
 ### MinMax
 
-- MinMax 增加了 `.min` `.max` API 返回一个 `dayjs` 来比较传入的 dayjs 实例的大小.
+- MinMax 增加了 `.min` `.max` API 返回一个 `dayjs` 来比较传入的 dayjs 实例的大小。
 
 ```javascript
 import minMax from 'dayjs/plugin/minMax'
@@ -400,6 +400,26 @@ dayjs.max(dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01'))
 dayjs.min([dayjs(), dayjs('2018-01-01'), dayjs('2019-01-01')])
 ```
 
+### Calendar
+
+- Calendar 增加了 `.calendar` API 返回一个 `string` 来显示日历时间。
+
+```javascript
+import calendar from 'dayjs/plugin/calendar'
+
+dayjs.extend(calendar)
+
+dayjs().calendar(dayjs('2008-01-01'))
+dayjs().calendar(null, {
+  sameDay: '[今天] HH:mm', // 今天 ( 今天 2:30 AM )
+  nextDay: '[明天]', // 明天 ( 明天 2:30 AM )
+  nextWeek: '[下]dddd', // 下周 ( Sunday at 2:30 AM )
+  lastDay: '[昨天]', // 昨天 ( 昨天 2:30 AM )
+  lastWeek: '[上] dddd', // 上周 ( Last Monday at 2:30 AM )
+  sameElse: 'DD/MM/YYYY' // 其他情况 ( 7/10/2011 )
+})
+```
+
 ## 自定义
 
 你可以根据需要自由的编写一个 Day.js 插件
diff --git a/src/index.js b/src/index.js
index 780ad3ba1..d0213dedb 100644
--- a/src/index.js
+++ b/src/index.js
@@ -219,6 +219,7 @@ class Dayjs {
     const arg = unit === C.D ? this.$D + (int - this.$W) : int
 
     if (unit === C.M || unit === C.Y) {
+      // clone is for badMutable plugin
       const date = this.clone().set(C.DATE, 1)
       date.$d[name](arg)
       date.init()