851
| Years | 
|---|
| Millennium | 
| 1st millennium | 
| Centuries | 
| Decades | 
| Years | 
| 851 by topic | 
|---|
| Leaders | 
| Categories | 
| 
 | 
| Gregorian calendar | 851 DCCCLI | 
| Ab urbe condita | 1604 | 
| Armenian calendar | 300 ԹՎ Յ | 
| Assyrian calendar | 5601 | 
| Balinese saka calendar | 772–773 | 
| Bengali calendar | 257–258 | 
| Berber calendar | 1801 | 
| Buddhist calendar | 1395 | 
| Burmese calendar | 213 | 
| Byzantine calendar | 6359–6360 | 
| Chinese calendar | 庚午年 (Metal Horse) 3548 or 3341 — to — 辛未年 (Metal Goat) 3549 or 3342 | 
| Coptic calendar | 567–568 | 
| Discordian calendar | 2017 | 
| Ethiopian calendar | 843–844 | 
| Hebrew calendar | 4611–4612 | 
| Hindu calendars | |
| - Vikram Samvat | 907–908 | 
| - Shaka Samvat | 772–773 | 
| - Kali Yuga | 3951–3952 | 
| Holocene calendar | 10851 | 
| Iranian calendar | 229–230 | 
| Islamic calendar | 236–237 | 
| Japanese calendar | Kashō 4 / Ninju 1 (仁寿元年) | 
| Javanese calendar | 748–749 | 
| Julian calendar | 851 DCCCLI | 
| Korean calendar | 3184 | 
| Minguo calendar | 1061 before ROC 民前1061年 | 
| Nanakshahi calendar | −617 | 
| Seleucid era | 1162/1163 AG | 
| Thai solar calendar | 1393–1394 | 
| Tibetan calendar | 阳金马年 (male Iron-Horse) 977 or 596 or −176 — to — 阴金羊年 (female Iron-Goat) 978 or 597 or −175 | 
Year 851 (DCCCLI) was a common year starting on Thursday of the Julian calendar.