1021
| Years | 
|---|
| Millennium | 
| 2nd millennium | 
| Centuries | 
| Decades | 
| Years | 
| 1021 by topic | 
|---|
| Leaders | 
| 
 | 
| Birth and death categories | 
| Births – Deaths | 
| Establishments and disestablishments categories | 
| Establishments – Disestablishments | 
| Gregorian calendar | 1021 MXXI | 
| Ab urbe condita | 1774 | 
| Armenian calendar | 470 ԹՎ ՆՀ | 
| Assyrian calendar | 5771 | 
| Balinese saka calendar | 942–943 | 
| Bengali calendar | 427–428 | 
| Berber calendar | 1971 | 
| English Regnal year | N/A | 
| Buddhist calendar | 1565 | 
| Burmese calendar | 383 | 
| Byzantine calendar | 6529–6530 | 
| Chinese calendar | 庚申年 (Metal Monkey) 3718 or 3511 — to — 辛酉年 (Metal Rooster) 3719 or 3512 | 
| Coptic calendar | 737–738 | 
| Discordian calendar | 2187 | 
| Ethiopian calendar | 1013–1014 | 
| Hebrew calendar | 4781–4782 | 
| Hindu calendars | |
| - Vikram Samvat | 1077–1078 | 
| - Shaka Samvat | 942–943 | 
| - Kali Yuga | 4121–4122 | 
| Holocene calendar | 11021 | 
| Igbo calendar | 21–22 | 
| Iranian calendar | 399–400 | 
| Islamic calendar | 411–412 | 
| Japanese calendar | Kannin 5 / Jian 1 (治安元年) | 
| Javanese calendar | 923–924 | 
| Julian calendar | 1021 MXXI | 
| Korean calendar | 3354 | 
| Minguo calendar | 891 before ROC 民前891年 | 
| Nanakshahi calendar | −447 | 
| Seleucid era | 1332/1333 AG | 
| Thai solar calendar | 1563–1564 | 
| Tibetan calendar | 阳金猴年 (male Iron-Monkey) 1147 or 766 or −6 — to — 阴金鸡年 (female Iron-Rooster) 1148 or 767 or −5 | 
Year 1021 (MXXI) was a common year starting on Sunday of the Julian calendar.