| Centuries: | 6th century · 7th century · 8th century |
| Decades: | 610s 620s 630s 640s 650s 660s 670s |
| Years: | 637 638 639 640 641 642 643 |
| 640 by topic | |
| Politics | |
| State leaders – Sovereign states | |
| Birth and death categories | |
| Births – Deaths | |
| Establishment and disestablishment categories | |
| Establishments – Disestablishments | |
| Gregorian calendar | 640 DCXL |
| Ab urbe condita | 1393 |
| Armenian calendar | 89 ԹՎ ՁԹ |
| Bahá'í calendar | -1204 – -1203 |
| Bengali calendar | 47 |
| Berber calendar | 1590 |
| Buddhist calendar | 1184 |
| Burmese calendar | 2 |
| Byzantine calendar | 6148 – 6149 |
| Chinese calendar | 己亥年十二月初三日 (3276/3336-12-3) — to —
庚子年十一月十三日(3277/3337-11-13) |
| Coptic calendar | 356 – 357 |
| Ethiopian calendar | 632 – 633 |
| Hebrew calendar | 4400 – 4401 |
| Hindu calendars | |
| - Bikram Samwat | 696 – 697 |
| - Shaka Samvat | 562 – 563 |
| - Kali Yuga | 3741 – 3742 |
| Holocene calendar | 10640 |
| Iranian calendar | 18 – 19 |
| Islamic calendar | 19 – 20 |
| Japanese calendar | |
| Korean calendar | 2973 |
| Thai solar calendar | 1183 |