Back 1840 Abkhazian 1840 Afrikaans 1840 ALS 1840 እ.ኤ.አ. Amharic 1840 AN 1840 Arabic 1840 ARY 1840 ARZ 1840 AST 1840 AVK
| Millennium: | 2nd millennium |
|---|---|
| Centuries: | 18th century – 19th century – 20th century |
| Decades: | 1810s 1820s 1830s – 1840s – 1850s 1860s 1870s |
| Years: | 1837 1838 1839 – 1840 – 1841 1842 1843 |
| Gregorian calendar | 1840 MDCCCXL |
| Ab urbe condita | 2593 |
| Armenian calendar | 1289 ԹՎ ՌՄՁԹ |
| Assyrian calendar | 6590 |
| Balinese saka calendar | 1761–1762 |
| Bengali calendar | 1247 |
| Berber calendar | 2790 |
| British Regnal year | 3 Vict. 1 – 4 Vict. 1 |
| Buddhist calendar | 2384 |
| Burmese calendar | 1202 |
| Byzantine calendar | 7348–7349 |
| Chinese calendar | 己亥年 (Earth Pig) 4536 or 4476 — to — 庚子年 (Metal Rat) 4537 or 4477 |
| Coptic calendar | 1556–1557 |
| Discordian calendar | 3006 |
| Ethiopian calendar | 1832–1833 |
| Hebrew calendar | 5600–5601 |
| Hindu calendars | |
| - Vikram Samvat | 1896–1897 |
| - Shaka Samvat | 1761–1762 |
| - Kali Yuga | 4940–4941 |
| Holocene calendar | 11840 |
| Igbo calendar | 840–841 |
| Iranian calendar | 1218–1219 |
| Islamic calendar | 1255–1256 |
| Japanese calendar | Tenpō 11 (天保１１年) |
| Javanese calendar | 1767–1768 |
| Julian calendar | Gregorian minus 12 days |
| Korean calendar | 4173 |
| Minguo calendar | 72 before ROC 民前72年 |
| Nanakshahi calendar | 372 |
| Thai solar calendar | 2382–2383 |
| Tibetan calendar | 阴土猪年 (female Earth-Pig) 1966 or 1585 or 813 — to — 阳金鼠年 (male Iron-Rat) 1967 or 1586 or 814 |
1840 (MDCCCXL) was a leap year starting on Wednesday of the Gregorian calendar and a leap year starting on Monday of the Julian calendar, the 1840th year of the Common Era (CE) and Anno Domini (AD) designations, the 840th year of the 2nd millennium, the 40th year of the 19th century, and the 1st year of the 1840s decade. As of the start of 1840, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.