| Letters | Expansion | Additional information |
| AD | Anno Domini | Latin "The year of Our Lord". Counting from the incarnation of Christ. |
| AL | Anno Lucis | Latin "The year of light" Equivalent to AD + 4000. |
| AM | Anno Mundi | Latin "The year of the world". Counting from the year of creation in Jewish history. Creation is accepted as 7 Oct. 3761 BC. |
| AUC | Ab Urbe Conditâ | Latin "Since the founding of the city (Rome)". |
| BC | Before Christ | Counts backwards from the incarnation of Christ. |
| BCE | Before Common Era | Equivalent to BC. |
| BP | Before Present | Counts backwards from the current year. |
| CE | Common Era | Equivalent to AD. |
| UT | Universal Time | The mean solar time at the meridian of Greenwich, UK. |
| UTC | Coordinated Universal Time | The universal standard of time based on atomic time |