| Millennium: | 1st millennium |
|---|---|
| Centuries: | 8th century – 9th century – 10th century |
| Decades: | 790s 800s 810s – 820s – 830s 840s 850s |
| Years: | 817 818 819 – 820 – 821 822 823 |
| 820 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 820 DCCCXX |
| Ab urbe condita | 1573 |
| Armenian calendar | 269 ԹՎ ՄԿԹ |
| Bahá'í calendar | -1024 – -1023 |
| Bengali calendar | 227 |
| Berber calendar | 1770 |
| Buddhist calendar | 1364 |
| Burmese calendar | 182 |
| Byzantine calendar | 6328 – 6329 |
| Chinese calendar | 己亥年十二月十二日 (3456/3516-12-12) — to —
庚子年十一月廿三日(3457/3517-11-23) |
| Coptic calendar | 536 – 537 |
| Ethiopian calendar | 812 – 813 |
| Hebrew calendar | 4580 – 4581 |
| Hindu calendars | |
| - Bikram Samwat | 876 – 877 |
| - Shaka Samvat | 742 – 743 |
| - Kali Yuga | 3921 – 3922 |
| Holocene calendar | 10820 |
| Iranian calendar | 198 – 199 |
| Islamic calendar | 204 – 205 |
| Japanese calendar | |
| Korean calendar | 3153 |
| Thai solar calendar | 1363 |