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Prepositions of time are small but critical words that tell us when something happens. The three most important prepositions of time in English are in, on, and at. Choosing the correct one depends on how specific the time reference is. Other prepositions of time include since, for, during, by, and until. This comprehensive guide will help you master all of them with clear rules, examples, and practice exercises.
Table of Contents
Overview: In, On, At
The three core prepositions of time follow a simple principle: as the time period gets more specific, the preposition changes from in (largest) to on (medium) to at (most specific).
| Preposition | Used For | Examples |
|---|---|---|
| at | Specific times, precise moments | at 5 PM, at noon, at midnight |
| on | Days and dates | on Monday, on July 4th, on my birthday |
| in | Months, years, seasons, centuries, longer periods | in January, in 2024, in summer, in the morning |
Memory Aid: Think of time as a container. At is a precise point (a dot). On is a surface (a day). In is a space you are inside (a month, year, or season).
At — Specific Times and Precise Moments
At is used for the most precise time references—clock times and specific moments.
Clock Times
The meeting starts at 9 AM.
I wake up at 6:30 every morning.
The train arrives at 3:15 PM.
Specific Time Points
at noon / at midday
at midnight
at sunrise / at sunset
at lunchtime / at dinnertime
Holidays and Festivals (as periods)
at Christmas (the holiday period)
at Easter
at the weekend (British English)
Fixed Expressions with At
at the moment, at present, at the same time, at night, at the age of...
On — Days and Dates
On is used for specific days and dates—one step broader than "at" but one step narrower than "in."
Days of the Week
I have a meeting on Monday.
We go shopping on Saturdays.
The exam is on Friday.
Specific Dates
She was born on March 15, 1990.
The project is due on the 1st of June.
We celebrate Independence Day on July 4th.
Special Days
on my birthday / on your wedding day
on Christmas Day (the specific day, not the period)
on New Year's Eve / on New Year's Day
Day + Part of Day
on Monday morning
on Friday evening
on Saturday night
In — Longer Periods of Time
In is used for the broadest time periods: months, years, seasons, centuries, and parts of the day.
Months
My birthday is in September.
It snows a lot in January.
Years and Decades
She graduated in 2020.
The internet became popular in the 1990s.
Seasons
Flowers bloom in spring.
We go skiing in winter.
Parts of the Day
in the morning / in the afternoon / in the evening
BUT: at night (exception!)
"In" for Future Time
In can also mean "after a period of time from now":
I'll be ready in five minutes. (five minutes from now)
The package will arrive in three days.
She will return in a week.
Since vs. For
Both since and for describe duration but in different ways.
| Since (point in time) | For (duration/length) |
|---|---|
| since 2010 | for 15 years |
| since Monday | for three days |
| since I was a child | for a long time |
| since breakfast | for several hours |
I have lived here since 2015. (starting point)
I have lived here for ten years. (length of time)
She has been waiting since 3 PM.
She has been waiting for two hours.
Remember: Since answers "since when?" and for answers "how long?" Both are commonly used with the present perfect tense.
During — Throughout a Period
During indicates that something happens within a particular time period. It is followed by a noun, not a number.
I fell asleep during the movie.
Many shops close during the holidays.
He learned a lot during his time abroad.
It rained during the night.
Do not confuse during with for: "during" tells us when (within what period), while "for" tells us how long.
By and Until (Till)
By — No Later Than
By means "at or before" a specific time. It sets a deadline.
Please finish the report by Friday. (on or before Friday)
I need to be at the airport by 6 AM.
The project must be completed by the end of the month.
Until / Till — Up to a Point
Until (or till) means "up to" a certain time. The action continues until that time and then stops.
I'll wait until 5 PM. (I'll stop waiting at 5 PM)
The shop is open until 9 PM.
We stayed at the party until midnight.
When No Preposition Is Needed
Some time expressions do not require a preposition. Generally, no preposition is used with last, next, this, that, every, each, all:
I saw her last week. (NOT "in last week")
We will go next Monday. (NOT "on next Monday")
This morning was cold. (NOT "in this morning")
She visits every summer. (NOT "in every summer")
Also no preposition with yesterday, today, tomorrow:
I will call you tomorrow. (NOT "on tomorrow")
She arrived yesterday. (NOT "on yesterday")
Common Mistakes to Avoid
Mistake 1: Mixing Up In/On/At
❌ I was born in July 15. → ✅ I was born on July 15.
❌ The meeting is at Monday. → ✅ The meeting is on Monday.
❌ She arrived on 3 PM. → ✅ She arrived at 3 PM.
Mistake 2: "At Night" vs. "In the Night"
✅ I can't sleep at night. (general — most common)
✅ I heard a noise in the night. (a specific night, literary)
Mistake 3: Unnecessary Preposition with Last/Next/This
❌ I'll see you on next Friday. → ✅ I'll see you next Friday.
Mistake 4: Confusing Since and For
❌ I have worked here since five years. → ✅ I have worked here for five years.
Practice Exercises
Fill in the correct preposition of time.
1. The flight departs _______ 7:30 AM.
Answer: at
2. My birthday is _______ December.
Answer: in
3. We have a meeting _______ Wednesday.
Answer: on
4. She has been studying _______ 2019.
Answer: since
5. I'll finish the work _______ two hours.
Answer: in
6. Please reply _______ the end of the day.
Answer: by
7. We waited _______ midnight.
Answer: until
8. It often rains _______ spring.
Answer: in
Prepositions of time may be small words, but using them correctly makes a big difference in how natural and accurate your English sounds. Master the in/on/at system, learn the nuances of since/for and by/until, and remember the exceptions. With practice, choosing the right preposition will become second nature.
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