Prepositions of Time (in / on / at)

What it means

in, on and at tell us when something happens. Think of a triangle from big to small: in for long periods, on for days, at for exact points in time.

How to make it

• in + long periods: in May, in 2025, in summer, in the 21st century
• in + parts of the day: in the morning, in the afternoon, in the evening
• on + days and dates: on Monday, on 5 June, on my birthday
• at + exact times: at 7 o'clock, at 3 p.m., at noon
• at + some fixed phrases: at night, at the weekend (British English – American English says "on the weekend")
• No preposition before this, next, last, every: next week, last Monday, this year, every day

When to use it

• A month: My birthday is in October.
• A day and a clock time: The meeting is on Tuesday at 3 p.m.
• Parts of the day: I like to read at night and exercise in the morning.
• With next / last / this / every – nothing: We're going to Bangkok next week.

Compare

• in the morning (any morning) → on Monday morning (a named day, so "on")
• in the evening → at night (a fixed phrase – not "in the night" for general habits)
• at the weekend (British) → on the weekend (American)

Common mistakes

• ❌ in Monday → ✅ on Monday (days take "on")
• ❌ We're going in next week. → ✅ We're going next week. (no preposition before next)
• ❌ at the morning → ✅ in the morning (parts of the day take "in", except "at night")