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The meeting is at 3pm, on Monday, in June. In one short sentence we have used the three most important prepositions of time — and choosing the wrong one is one of the surest signs that English is not your first language.
This guide starts with the core trio of at, on and in, then covers the prepositions that learners find trickiest: by and until, for and since, during, from...to, and before, after and ago. For a fuller reference, see our prepositions of time grammar page.
Key Takeaways
- At for clock times and fixed points (at 6pm, at night, at the weekend in British English).
- On for days and dates (on Monday, on 5 May, on my birthday).
- In for months, years, seasons and parts of the day (in July, in 2026, in the morning).
- Use for + duration, since + start point; by = deadline, until = up to a point.
- Avoid the classic errors in Monday and since three hours — say on Monday and for three hours.
The Core Three: At, On, In
Just as with place, the choice between at, on and in follows a scale from the most precise to the broadest. At is a point on the clock, on is a single day, and in is a longer stretch of time.
| Preposition | Used for | Examples |
|---|---|---|
| at | Clock times, fixed points | at 6pm, at noon, at night, at the weekend |
| on | Days and dates | on Monday, on 5 May, on my birthday |
| in | Months, years, seasons, parts of day | in July, in 2026, in winter, in the morning |
One famous exception breaks the pattern: although we use in for parts of the day (in the morning, in the afternoon, in the evening), we say at night, not in the night in most contexts.
British English says at the weekend, while American English prefers on the weekend. Both are correct in their own variety, so pick the one that matches the English you are learning and stay consistent.
Fixed Phrases with At, On and In
Many time expressions are best learned as whole chunks. The table below gathers the most useful ones.
| at | on | in |
|---|---|---|
| at midnight | on Fridays | in the 1990s |
| at lunchtime | on New Year’s Day | in spring |
| at the moment | on Monday morning | in the 21st century |
| at Christmas | on Christmas Day | in five minutes |
| at the same time | on time | in time |
Watch the difference between on time (punctual, exactly when arranged) and in time (early enough, with some margin). Also note that we use in to mean “after a period”: I’ll be ready in ten minutes points to the end of that period.
For vs Since
These two are constantly confused, yet the rule is clear. For answers “how long?” with a duration; since answers “starting when?” with a point in time.
for + duration
- A length of time
- for two hours, for three days
- for ten years, for a while
- I have lived here for five years.
since + starting point
- A point when something began
- since 2020, since Monday
- since I was a child
- I have lived here since 2021.
Both pair naturally with the present perfect tense. If you can replace the phrase with “starting from”, use since; if it answers “for how long”, use for.
By vs Until
Another classic pair. By sets a deadline for a single action; until (or till) marks how long a continuous situation lasts before it stops.
by = not later than; until = up to a point
| Word | Meaning | Example |
|---|---|---|
| by | At any point before a deadline | Finish the report by Friday. |
| until / till | Continuing up to a point, then stopping | I will wait until Friday. |
So I must leave by 6pm means leave at any moment before six, while I will stay until 6pm means stay right up to six. Use by for finishing and until for continuing.
During, From...To, Before, After and Ago
The remaining prepositions round out your toolkit for talking about time.
| Word | Meaning | Example |
|---|---|---|
| during | Within a period (+ noun) | It rained during the night. |
| from...to / till | Start to end of a period | We work from 9 to 5. |
| before | Earlier than an event | Wash your hands before dinner. |
| after | Later than an event | We left after the film. |
| ago | Back from now (+ past tense) | I arrived two hours ago. |
Remember that ago comes after the time expression and is used with the past simple: three days ago, not ago three days. Compare it with before, which counts back from another point you mention rather than from now.
Common Mistakes to Avoid
A few errors crop up over and over. Fix these and your English will sound noticeably more natural.
See you in Monday. → say: See you on Monday.
I have been here since three hours. → say: I have been here for three hours.
The shop opens at the morning. → say: The shop opens in the morning.
I will stay by 6pm. → say: I will stay until 6pm.
I met him ago two years. → say: I met him two years ago.
For a broader look at how prepositions work across place, time and movement, see our complete prepositions guide, and learn the location rules in our prepositions of place guide.
In writing tasks, link your ideas with a range of time prepositions — during, by, until, before and after — rather than repeating when. Examiners reward this control of cohesive devices, provided the core at/on/in choices stay accurate.
Practise Prepositions of Time
Test yourself with gap-fill exercises and get instant feedback on every answer.
Complete the SentenceExercises to Practise on LexFizz
- Complete the Sentence — fill in the correct preposition of time (at, on, in and more)
- Cloze Dropdown — choose the right preposition from a dropdown menu
- True or False — identify correct and incorrect preposition usage
- Quiz — multiple-choice questions on prepositions of time
- Flash Cards — review fixed phrases with spaced repetition
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Frequently Asked Questions
Prepositions of time are words that show when something happens or for how long. The three most important are at, on and in, but the group also includes by, until, for, since, during, from...to, before, after and ago. For example, The meeting is at 3pm on Monday in June uses all three core prepositions. Choosing the right one depends on whether you are talking about a clock time, a day or date, or a longer period such as a month or year.
Use at for clock times and precise points (at 6pm, at night, at the weekend in British English), on for days and dates (on Monday, on 5 May, on my birthday), and in for longer periods such as months, years, seasons and parts of the day (in July, in 2026, in winter, in the morning). A simple scale is that at is the most precise point, on is a single day, and in is a longer stretch of time.
We use at for exact clock times (at 7 o’clock, at 9.30) and for certain fixed expressions: at night, at noon, at midnight, at lunchtime, at the moment, at the same time and, in British English, at the weekend and at Christmas. Think of at as pointing to a precise moment on the clock or to a short, fixed period treated as a single point in time.
We use on for days and dates: on Monday, on Fridays, on 5 May, on 25 December, on New Year’s Day and on my birthday. We also use on with specific named days that include a part of the day, as in on Monday morning or on the night of the storm. If you are naming a particular day or date, on is almost always the correct choice.
We use in for longer periods: months (in July), years (in 2026), seasons (in summer), centuries (in the 21st century) and parts of the day (in the morning, in the afternoon, in the evening). Note the exception at night. We also use in to mean after a period of time, as in I’ll be ready in ten minutes, which points to the end of that period rather than a duration.
Use for with a length of time to say how long something lasts: for two hours, for three days, for ten years. Use since with a starting point to say when something began: since 2020, since Monday, since I was a child. So we say I have lived here for five years (duration) but I have lived here since 2021 (start point). Both are common with the present perfect tense.
Use by to mean “not later than” a deadline: Finish the report by Friday means complete it at any point before Friday. Use until (or till) to mean a situation continues up to a point and then stops: I will wait until Friday means the waiting continues right up to Friday. In short, by marks a deadline for a single action, while until marks the end of a continuous one.
Ago measures back from now and goes after the time expression with a past tense: I arrived two hours ago. Before and after show the order of two events: Wash your hands before dinner and We left after the film. Note that ago counts back from the present moment, whereas before counts back from another point in the past or future that you mention.
In Monday is wrong because days take on, so the correct form is on Monday. Since three hours is wrong because since needs a starting point, not a length of time; to express duration we use for, so the correct form is for three hours. These are two of the most common preposition-of-time mistakes, and fixing them makes a big difference to how natural your English sounds.
Practise by: (1) Writing your weekly schedule using at, on and in for times, days and months. (2) Making pairs of sentences with for and since, and with by and until, to feel the difference. (3) Using LexFizz’s Complete the Sentence and Cloze Dropdown games to choose the correct preposition. (4) Learning fixed phrases such as at night, in the morning and on Monday as whole chunks. (5) Correcting common errors like in Monday and since three hours until the right form feels automatic.
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