When to use AT, IN, ON? Prepositions of time
We use:
- at for a PRECISE TIME
- in for MONTHS, YEARS, CENTURIES and LONG PERIODS
- on for DAYS and DATES
Look at these examples:
- I have a meeting at 9am.
- The shop closes at midnight.
- Jane went home at lunchtime.
- In England, it often snows in December.
- Do you think we will go to Jupiter in the future?
- There should be a lot of progress in the next century.
- Do you work on Mondays?
- Her birthday is on 20 November.
- Where will you be on New Year’s Day?
Look at these examples:
Notice the use of the preposition of time at in the following standard expressions:

*Note that in some varieties of English people say “on the weekend” and “on Christmas”.
Notice the use of the prepositions of time in and on in these common expressions:

*Note that in some varieties of English people say “on the weekend” and “on Christmas”.
When we say last, next, every, this – we do NOT also use at, in, on.
- I went to London last June. (not in last June)
- He’s coming back next Tuesday. (not on next Tuesday)
- I go home every Easter. (not at every Easter)
- We’ll call you this evening. (not in this evening)

thank you for your help