| Millennium: | 2nd millennium |
|---|---|
| Centuries: | |
| Decades: | |
| Years: |
| 1800 by topic |
|---|
| Arts and science |
| Countries |
| Lists of leaders |
| Birth and death categories |
| Establishments and disestablishments categories |
| Works category |
| Gregorian calendar | 1800 MDCCC |
| French Republican calendar | 8–9 |
| Ab urbe condita | 2553 |
| Armenian calendar | 1249 ԹՎ ՌՄԽԹ |
| Assyrian calendar | 6550 |
| Balinese saka calendar | 1721–1722 |
| Bengali calendar | 1207 |
| Berber calendar | 2750 |
| British Regnal year | 40 Geo. 3 – 41 Geo. 3 |
| Buddhist calendar | 2344 |
| Burmese calendar | 1162 |
| Byzantine calendar | 7308–7309 |
| Chinese calendar | 己未年 (Earth Goat) 4497 or 4290 — to — 庚申年 (Metal Monkey) 4498 or 4291 |
| Coptic calendar | 1516–1517 |
| Discordian calendar | 2966 |
| Ethiopian calendar | 1792–1793 |
| Hebrew calendar | 5560–5561 |
| Hindu calendars | |
| - Vikram Samvat | 1856–1857 |
| - Shaka Samvat | 1721–1722 |
| - Kali Yuga | 4900–4901 |
| Holocene calendar | 11800 |
| Igbo calendar | 800–801 |
| Iranian calendar | 1178–1179 |
| Islamic calendar | 1214–1215 |
| Japanese calendar | Kansei 12 (寛政１２年) |
| Javanese calendar | 1726–1727 |
| Julian calendar | Gregorian minus 11 or 12 days |
| Korean calendar | 4133 |
| Minguo calendar | 112 before ROC 民前112年 |
| Nanakshahi calendar | 332 |
| Thai solar calendar | 2342–2343 |
| Tibetan calendar | 阴土羊年 (female Earth-Goat) 1926 or 1545 or 773 — to — 阳金猴年 (male Iron-Monkey) 1927 or 1546 or 774 |
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1800 (MDCCC) was an exceptional common year starting on Wednesday of the Gregorian calendar and a leap year starting on Sunday of the Julian calendar, the 1800th year of the Common Era (CE) and Anno Domini (AD) designations, the 800th year of the 2nd millennium, the 100th and last year of the 18th century, and the 1st year of the 1800s decade. As of the start of 1800, the Gregorian calendar was 11 days ahead of the Julian calendar, which remained in localized use until 1923.
As of March 1 (O.S. February 18), when the Julian calendar acknowledged a leap day and the Gregorian calendar did not, the Julian calendar fell one day further behind, bringing the difference to 12 days until February 28 (O.S. February 16), 1900.