Prepositions of time (in, on, at)

When you want to say when something happens, English uses small words called prepositions of time. The three most important ones are in, on, and at — and each one goes with a different kind of time word.

Quick shortcut: in often goes with longer periods (months, years, seasons), on with days and dates, at with exact times. In July, on Monday, at 3 o'clock.

In: longer periods of time

Use in for months, years, seasons, and other longer periods:

• My birthday is in July.
• She was born in 2015.
• We usually go to the beach in summer (or in the summer).
• I always check my phone in the morning.

Use in the morning/afternoon/evening when speaking generally. But with a specific day, switch to on: on Monday morning, on Friday evening, on Saturday night. A specific future point in time, like two weeks from now, also uses in: See you in two weeks.

On: days and dates

Use on for days of the week and specific dates:

• The meeting is on Tuesday.
• We're having a party on 5 May.
• I don't work on weekends. (American English; British English usually says at weekends, see below)

Note: for the general meaning of "during the night," English uses at night, not in: I sleep well at night. But with a specific day, it's on: on Friday night. See below for more on at.

At: exact times

Use at for precise clock times and a few fixed time expressions:

• The film starts at 8 p.m.
• I always feel tired at night.
• We're staying with family at Christmas.

✅ at night, never ❌ in night — this is a fixed exception worth remembering.

At the weekend and on the weekend are both correct, just in different dialects: British English usually says at the weekend / at weekends, and American English usually says on the weekend / on weekends.

At Christmas and at Easter mean during the whole holiday period. For one specific day, switch to on: on Christmas Day, on Easter Sunday.

No preposition at all

A few time expressions never take a preposition — adding one is a common mistake:

• ✅ I'll see you next week. → ❌ I'll see you on next week.
• ✅ We arrived last night. → ❌ We arrived at last night.
• ✅ Let's meet this afternoon. → ❌ Let's meet on this afternoon.
• ✅ See you tomorrow. → ❌ See you at tomorrow.

Words like next, last, this, every, and tomorrow/today/yesterday already tell you when — they don't need in/on/at in front of them.

Asking "when"

Questions about time usually start with when or what time. The answer may use in, on, at, or no preposition at all, depending on the time word:

• When is your birthday? — It's in July.
• What time does the shop open? — It opens at 9 o'clock.
• When do you usually relax? — On Sundays, and in the evening.

Common mistakes

• ❌ I was born on 2015. → ✅ I was born in 2015. (years take in, not on)
• ❌ See you in Monday. → ✅ See you on Monday. (days take on, not in)
• ❌ The train leaves in 9 o'clock. → ✅ The train leaves at 9 o'clock. (clock times take at, not in)
• ❌ I sleep well in night. → ✅ I sleep well at night. (at night is a fixed exception)
• ❌ I'll call you on next week. → ✅ I'll call you next week. (no preposition before next/last/this)

Quick check

Which preposition fits (in / on / at / no preposition)?

1. My birthday is ____ September.
2. The party is ____ Saturday.
3. The film starts ____ 7 o'clock.
4. I never work ____ night.
5. Let's meet ____ next Friday.

Key takeaways

• In = longer periods (months, years, seasons, parts of the day).
• On = days and dates.
• At = exact clock times, plus the fixed expressions at night, at the weekend, at Christmas.
• Words like next, last, this, and tomorrow/today/yesterday take no preposition at all.
• This article covers when something happens. For where something is, see Prepositions of place.