| Millennium: | 1st millennium |
|---|---|
| Centuries: | 8th century – 9th century – 10th century |
| Decades: | 810s 820s 830s – 840s – 850s 860s 870s |
| Years: | 839 840 841 – 842 – 843 844 845 |
| 842 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 842 DCCCXLII |
| Ab urbe condita | 1595 |
| Armenian calendar | 291 ԹՎ ՄՂԱ |
| Bahá'í calendar | -1002 – -1001 |
| Bengali calendar | 249 |
| Berber calendar | 1792 |
| Buddhist calendar | 1386 |
| Burmese calendar | 204 |
| Byzantine calendar | 6350 – 6351 |
| Chinese calendar | 辛酉年十一月十六日 (3478/3538-11-16) — to —
壬戌年十一月廿六日(3479/3539-11-26) |
| Coptic calendar | 558 – 559 |
| Ethiopian calendar | 834 – 835 |
| Hebrew calendar | 4602 – 4603 |
| Hindu calendars | |
| - Bikram Samwat | 898 – 899 |
| - Shaka Samvat | 764 – 765 |
| - Kali Yuga | 3943 – 3944 |
| Holocene calendar | 10842 |
| Iranian calendar | 220 – 221 |
| Islamic calendar | 227 – 228 |
| Japanese calendar | |
| Korean calendar | 3175 |
| Thai solar calendar | 1385 |