991
| Years | 
|---|
| Millennium | 
| 1st millennium | 
| Centuries | 
| Decades | 
| Years | 
| 991 by topic | 
|---|
| Leaders | 
| Categories | 
| 
 | 
| Gregorian calendar | 991 CMXCI | 
| Ab urbe condita | 1744 | 
| Armenian calendar | 440 ԹՎ ՆԽ | 
| Assyrian calendar | 5741 | 
| Balinese saka calendar | 912–913 | 
| Bengali calendar | 397–398 | 
| Berber calendar | 1941 | 
| Buddhist calendar | 1535 | 
| Burmese calendar | 353 | 
| Byzantine calendar | 6499–6500 | 
| Chinese calendar | 庚寅年 (Metal Tiger) 3688 or 3481 — to — 辛卯年 (Metal Rabbit) 3689 or 3482 | 
| Coptic calendar | 707–708 | 
| Discordian calendar | 2157 | 
| Ethiopian calendar | 983–984 | 
| Hebrew calendar | 4751–4752 | 
| Hindu calendars | |
| - Vikram Samvat | 1047–1048 | 
| - Shaka Samvat | 912–913 | 
| - Kali Yuga | 4091–4092 | 
| Holocene calendar | 10991 | 
| Iranian calendar | 369–370 | 
| Islamic calendar | 380–381 | 
| Japanese calendar | Shōryaku 2 (正暦2年) | 
| Javanese calendar | 892–893 | 
| Julian calendar | 991 CMXCI | 
| Korean calendar | 3324 | 
| Minguo calendar | 921 before ROC 民前921年 | 
| Nanakshahi calendar | −477 | 
| Seleucid era | 1302/1303 AG | 
| Thai solar calendar | 1533–1534 | 
| Tibetan calendar | 阳金虎年 (male Iron-Tiger) 1117 or 736 or −36 — to — 阴金兔年 (female Iron-Rabbit) 1118 or 737 or −35 | 
Year 991 (CMXCI) was a common year starting on Thursday of the Julian calendar.