| Millennium: | 1st millennium |
|---|---|
| Centuries: | |
| Decades: | |
| Years: |
| AD 21 by topic |
|---|
| Leaders |
| Categories |
| Gregorian calendar | AD 21 XXI |
| Ab urbe condita | 774 |
| Assyrian calendar | 4771 |
| Balinese saka calendar | N/A |
| Bengali calendar | −572 |
| Berber calendar | 971 |
| Buddhist calendar | 565 |
| Burmese calendar | −617 |
| Byzantine calendar | 5529–5530 |
| Chinese calendar | 庚辰年 (Metal Dragon) 2718 or 2511 — to — 辛巳年 (Metal Snake) 2719 or 2512 |
| Coptic calendar | −263 – −262 |
| Discordian calendar | 1187 |
| Ethiopian calendar | 13–14 |
| Hebrew calendar | 3781–3782 |
| Hindu calendars | |
| - Vikram Samvat | 77–78 |
| - Shaka Samvat | N/A |
| - Kali Yuga | 3121–3122 |
| Holocene calendar | 10021 |
| Iranian calendar | 601 BP – 600 BP |
| Islamic calendar | 619 BH – 618 BH |
| Javanese calendar | N/A |
| Julian calendar | AD 21 XXI |
| Korean calendar | 2354 |
| Minguo calendar | 1891 before ROC 民前1891年 |
| Nanakshahi calendar | −1447 |
| Seleucid era | 332/333 AG |
| Thai solar calendar | 563–564 |
| Tibetan calendar | 阳金龙年 (male Iron-Dragon) 147 or −234 or −1006 — to — 阴金蛇年 (female Iron-Snake) 148 or −233 or −1005 |
AD 21 (XXI) was a common year starting on Wednesday of the Julian calendar. At the time, it was known as the Year of the Consulship of Tiberius and Drusus (or, less frequently, year 774 Ab urbe condita). The denomination AD 21 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.