| Millennium: | 1st millennium |
|---|---|
| Centuries: | |
| Decades: | |
| Years: |
| Gregorian calendar | 999 CMXCIX |
| Ab urbe condita | 1752 |
| Armenian calendar | 448 ԹՎ ՆԽԸ |
| Assyrian calendar | 5749 |
| Bengali calendar | 406 |
| Berber calendar | 1949 |
| Buddhist calendar | 1543 |
| Burmese calendar | 361 |
| Byzantine calendar | 6507–6508 |
| Chinese calendar |
戊戌年 (Earth Dog) 3695 or 3635 — to — 己亥年 (Earth Pig) 3696 or 3636 |
| Coptic calendar | 715–716 |
| Discordian calendar | 2165 |
| Ethiopian calendar | 991–992 |
| Hebrew calendar | 4759–4760 |
| Hindu calendars | |
| - Vikram Samvat | 1055–1056 |
| - Shaka Samvat | 920–921 |
| - Kali Yuga | 4099–4100 |
| Holocene calendar | 10999 |
| Iranian calendar | 377–378 |
| Islamic calendar | 389–390 |
| Japanese calendar |
Chōtoku 5 / Chōhō 1 (長保元年) |
| Javanese calendar | 900–901 |
| Julian calendar | 999 CMXCIX |
| Korean calendar | 3332 |
| Minguo calendar | 913 before ROC 民前913年 |
| Nanakshahi calendar | −469 |
| Seleucid era | 1310/1311 AG |
| Thai solar calendar | 1541–1542 |
Year 999 (CMXCIX) was a common year starting on Sunday (link will display the full calendar) of the Julian calendar. Depending on how one defines a millennium, 999 was either the last or second-to-last year of the first millennium.