Prepositions of time show when something happens or how long it lasts. Use at for exact times, on for days and dates, and in for months, years, seasons and parts of the day. Use for with a length of time, since with a starting point, and by or until with a deadline or an end point.
In, on and at for points in time
Think of a funnel. At is the narrowest, for exact points. On is for days and dates. In is the widest, for longer periods.
Use at for clock times and short moments: at nine o'clock, at noon, at midnight, at the moment. Use on for days and dates: on Monday, on 5 March, on my birthday, on Friday morning. Use in for months, years, seasons, centuries and parts of the day: in July, in 2024, in winter, in the twenty-first century, in the morning.
- at: at 8.30, at night, at the weekend, at Christmas
- on: on Tuesday, on 12 June, on New Year's Day, on Sunday evening
- in: in April, in 1998, in the summer, in the afternoon
Some exceptions to learn
A few fixed phrases break the funnel rule. We say at night, but in the morning, in the afternoon and in the evening. In British English we say at the weekend for one weekend and at weekends for a regular habit. American English says on the weekend and on weekends. We say at Christmas and at Easter for the festival period, but on Christmas Day for one date.
When you add a day to a part of the day, the preposition changes: on Monday morning, on Friday night. The day decides the preposition. Do not say in Monday morning.
- at night · in the evening
- on Friday · on Friday afternoon
For, since and during
For answers how long, and it goes with a length of time: for two hours, for six months, for a long time. Since answers from when, and it goes with a point in the past: since 2020, since Monday, since I was a child. Both usually go with the present perfect: I have lived here for five years. I have lived here since 2019.
During goes with a noun that names an event or a period: during the lecture, during the summer, during my studies. It answers when something happened inside that period. Do not use during with a number of hours or days: say for three weeks, not during three weeks.
By, until, before and after
Until means up to a point and a situation continues: I studied until midnight. By means no later than a point, usually for a deadline or a result: I must finish the report by Friday. The difference is that until describes a continuing action, and by describes something that happens before a limit.
Before and after link a time to a point or an event: before the exam, after lunch, before 2020. Within means inside a period of time: The results arrive within ten days. From ... to or from ... until shows the beginning and the end: The library is open from nine to five.
In time and on time
These two phrases look similar, but they have different meanings. On time means at the planned time, neither late nor early: The train arrived on time. In time means early enough to do something: We arrived in time to catch the train. A third phrase, in the end, means finally, after a long process.
Also remember the difference between in and within. I will call you in an hour means after one hour. I will call you within an hour means at any moment up to one hour.
Mistakes to avoid
The most common error is using in for everything: in Monday, in 5 May, in the night. Say on Monday, on 5 May, at night. The second is using since or for with the wrong tense: I live here since 2020 should be I have lived here since 2020. The third is leaving out the preposition when it is needed, such as I will see you Friday, which is common in American English and informal speech, but careful British writing says on Friday.
Finally, do not add a preposition before words like next, last, this, every, tomorrow and yesterday. Say next week, last year and every day, not in next week.
Who finds this hard?
- Spanish speakers: Spanish uses en for months and years, a for exact times and no preposition for many days, so learners often choose in for every time word.
- Italian speakers: Italian uses in for months and a for exact times and often uses no preposition before days, so on Monday can be a problem.
- Portuguese speakers: Portuguese uses em for days, months and years, so learners often say in Monday or in the weekend.
- Arabic speakers: Arabic uses the same small word for many time expressions, so learners often use in where English needs on or at.
IELTS tip
In Writing Task 1, time prepositions are central: in 2010, between 2005 and 2015, from March to June, by the end of the period. Use since and for with the present perfect for trends up to now, and check that every date has the right small word before it.
Frequently asked questions
When do I use in, on and at for time?
Use at for exact times, on for days and dates, and in for months, years, seasons and parts of the day.
What is the difference between for and since?
For goes with a length of time, such as for three years. Since goes with a starting point, such as since 2021.
What is the difference between by and until?
By means no later than a time and is used for deadlines. Until means up to a time and goes with an action that continues.
Do I say at the weekend or on the weekend?
British English usually says at the weekend. American English says on the weekend. Both are understood.
Sources
- Swan, M. (2016). Practical English Usage (4th ed.). Oxford University Press.
- Carter, R. and McCarthy, M. (2006). Cambridge Grammar of English. Cambridge University Press.