| Millennium: | 1st millennium |
|---|---|
| Centuries: | 8th century – 9th century – 10th century |
| Decades: | 810s 820s 830s – 840s – 850s 860s 870s |
| Years: | 837 838 839 – 840 – 841 842 843 |
| 840 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 840 DCCCXL |
| Ab urbe condita | 1593 |
| Armenian calendar | 289 ԹՎ ՄՁԹ |
| Bahá'í calendar | -1004 – -1003 |
| Bengali calendar | 247 |
| Berber calendar | 1790 |
| Buddhist calendar | 1384 |
| Burmese calendar | 202 |
| Byzantine calendar | 6348 – 6349 |
| Chinese calendar | 己未年十一月廿三日 (3476/3536-11-23) — to —
庚申年十二月初四日(3477/3537-12-4) |
| Coptic calendar | 556 – 557 |
| Ethiopian calendar | 832 – 833 |
| Hebrew calendar | 4600 – 4601 |
| Hindu calendars | |
| - Bikram Samwat | 896 – 897 |
| - Shaka Samvat | 762 – 763 |
| - Kali Yuga | 3941 – 3942 |
| Holocene calendar | 10840 |
| Iranian calendar | 218 – 219 |
| Islamic calendar | 225 – 226 |
| Japanese calendar | |
| Korean calendar | 3173 |
| Thai solar calendar | 1383 |
Other Uses[1]