| Millennium: | 1st millennium BC |
|---|---|
| Centuries: | 2nd century BC – 1st century BC – 1st century |
| Decades: | 110s BC 100s BC 90s BC – 80s BC – 70s BC 60s BC 50s BC |
| Years: | 84 BC 83 BC 82 BC – 81 BC – 80 BC 79 BC 78 BC |
| 81 BC by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishments and disestablishments categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 81 BC |
| Ab urbe condita | 673 |
| Armenian calendar | N/A |
| Bahá'í calendar | -1924 – -1923 |
| Bengali calendar | -673 |
| Berber calendar | 870 |
| Buddhist calendar | 464 |
| Burmese calendar | -718 |
| Byzantine calendar | 5428 – 5429 |
| Chinese calendar | [[Sexagenary cycle|]]年 (2556/2616) — to —
子年(2557/2617) |
| Coptic calendar | -364 – -363 |
| Ethiopian calendar | -88 – -87 |
| Hebrew calendar | 3680 – 3681 |
| Hindu calendars | |
| - Bikram Samwat | -24 – -23 |
| - Shaka Samvat | N/A |
| - Kali Yuga | 3021 – 3022 |
| Holocene calendar | 9920 |
| Iranian calendar | 702 BP – 701 BP |
| Islamic calendar | 724 BH – 723 BH |
| Japanese calendar | |
| Korean calendar | 2253 |
| Thai solar calendar | 463 |
Year 81 BC was a year of the pre-Julian calendar.