Prepositions of Time
At, on, in — when things happen. Learn the rules, then practise.
Show rules
At, on, in for time
The three core time prepositions follow a "zoom" rule: at for precise points, on for days, in for longer periods.
| Preposition | Use for | Examples |
|---|---|---|
| at | clock times, festivals, night, mealtimes | at 9 o'clock, at Christmas, at night, at dinner |
| on | days and dates | on Monday, on 5 June, on New Year's Day |
| in | months, years, seasons, centuries, parts of the day | in July, in 2020, in summer, in the morning |
✅ The meeting starts at 9 o'clock.
✅ We have a test on Monday.
✅ Her birthday is in July.
Watch out: it's at night but in the morning / afternoon / evening. Use on for a specific day's part: on Monday morning.
For and Since
- for + a period of time (how long): for two hours, for three years
- since + a point in time (the starting moment): since 2015, since Monday
✅ We waited for two hours.
✅ She has lived here since 2015.
During and While
- during + a noun: during the film, during the summer
- while + a clause (subject + verb): while I was watching the film
Until and By
| until | up to a point, continuously — something keeps happening |
| by | at or before a deadline — a single action happens before then |
✅ The shop is open until midnight. (open continuously)
✅ Please finish the report by Friday. (the deadline)
In and Ago
- in + a period = the future, counting forward from now: The train leaves in ten minutes.
- ago = the past, counting back from now: They left three years ago.
Common mistakes
| ❌ | ✅ |
|---|---|
| The test is at Monday. | The test is on Monday. |
| The meeting is in 9 o'clock. | The meeting is at 9 o'clock. |
| I've known her since two years. | I've known her for two years. |
| He slept during I was talking. | He slept while I was talking. |
| Finish it until Friday. | Finish it by Friday. |
Frequently Asked Questions
When do you use 'at', 'on', and 'in' for time?
Use 'at' for clock times, festivals, and night (at 9 o'clock, at Christmas, at night). Use 'on' for days and dates (on Monday, on 5 June, on my birthday). Use 'in' for months, years, seasons, centuries, and parts of the day (in July, in 2020, in summer, in the morning). The rule is a zoom: 'at' for precise points, 'on' for days, 'in' for longer periods.
What is the difference between 'for' and 'since'?
Use 'for' with a period of time — how long something lasts: 'for two hours', 'for three years'. Use 'since' with a point in time — the moment something started: 'since 2015', 'since Monday', 'since last summer'. A common error is 'since two hours' — it should be 'for two hours'.
What is the difference between 'until' and 'by'?
Use 'until' for something that continues up to a point in time: 'The shop is open until midnight.' Use 'by' for a deadline — a single action must be completed at or before that time: 'Finish the report by Friday.' 'Until' = continuous; 'by' = deadline.
What is the difference between 'during' and 'while'?
Use 'during' before a noun: 'during the film', 'during the summer'. Use 'while' before a clause with a subject and verb: 'while I was watching the film'. They express the same idea but follow different grammar — 'during' + noun, 'while' + clause.