Grammar · Sentence structure
Prepositions of time
Formula: in · on · at · since · for · ago…
B1
Quick answer
The 4 main uses
1. In: months, years, parts of the day
Use in for months, years and parts of the day. Be careful: in the morning, but at night.
“In March, in 2020, in the morning.”
2. On: days and dates
Use on for days of the week, dates and special days like your birthday.
“On Monday, on July 4th, on my birthday.”
3. At: clock times and festivals
Use at for clock times (at 8 o'clock, at noon), for festivals (at Christmas) and in at night.
“At 8 o'clock, at noon, at Christmas, at night.”
4. Since / for: from then until now
Since + a starting point. For + a length of time. You often use them with the Present Perfect.
“Since 2015, for 3 years.”
Signal words
Some words almost always go with this tense: if you see one in the sentence, it is a good clue.
since
from a starting point until now
“I have lived here since 2015.”
for
for a length of time
“I have lived here for 9 years.”
ago
back in the past from now (with the Past Simple)
“I met her two years ago.”
during
in a period of time (all through it, or at one point in it)
“I read during the journey.”
by
not later than
“I'll finish by Monday.”
until / till
up to a point in time, and then it stops
“Wait until 5 pm.”
Common mistakes to avoid
Since vs for
Since + an exact starting point (since 2015, since Monday, since I was a child). For + a length of time (for 3 years, for 5 hours, for a long time). If something started in the past and is still true, use the Present Perfect: I have lived here since 2015 / for three years ✓, I live here for 3 years ✗. You can also use for with other tenses: I lived there for three years (and I do not live there now).
Ago with the Past Simple, not the Present Perfect
Ago means “back in the past from now”. Use it only with the Past Simple: I met her two years ago ✓ / I have met her two years ago ✗.
In the morning but at night
This one is irregular: in the morning, in the afternoon, in the evening, but at night (not in the night).
Related pages: Prepositions of time
Pages on a similar topic or with a similar use, so you can keep exploring.
Going further
Prepositions of time: often tested in the English contest
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Frequently asked questions
What is the difference between in, on and at for time?+
In = months, years, parts of the day (in March, in 2020, in the morning). On = days, dates (on Monday, on July 4th). At = clock times, festivals, night (at 8, at Christmas, at night).
When do you use since and for?+
Since + a starting point (since 2015, since Monday). For + a length of time (for 3 years, for 5 hours). With the Present Perfect, both show a situation that is still true now: I have lived here since 2015 / for 9 years.
How do you use ago in English?+
Ago means “back in the past from now”. It comes after the length of time: two years ago, ten minutes ago. Use it only with the Past Simple: I saw her two years ago (not I have seen her two years ago).
Why do we say at night and not in the night?+
It is a fixed expression. We say in the morning, in the afternoon, in the evening, but at night. In the night exists, but it is less common.
Is it on Monday or in Monday?+
On Monday. Days of the week take on: on Monday, on Tuesday, on my birthday, on July 4th. Years and months take in.
Updated on 6 November 2026 by the Big Challenge teaching team. Every year, more than 500,000 students across Europe take part in our English contest, created in 1999. Our teaching approach →
The Big Challenge · Updated on 6 November 2026 · Source: www.thebigchallenge.com/bl/academy/learn-english/grammar/prepositions-of-time
© The Big Challenge. Copying allowed for classroom use. Every year, more than 500,000 students across Europe take part in our English contest, created in 1999.