in, on, at

The three words go from short to long: at for a point in time, on for a day, in for anything longer.

At

At is for clock times and a few short times and holidays.

• at six, at half past nine, at midnight, at lunchtime
• at night
• at Christmas, at Easter

On

On is for days and dates. On Mondays means every Monday.

• on Monday, on Mondays, on Friday morning
• on 3 May, on my birthday, on Christmas Day

In

In is for months, years, seasons and longer times, and for parts of the day.

• in July, in 2025, in winter
• in the morning, in the afternoon, in the evening

In the morning, but at night. With a day, it's on: on Monday morning.

No preposition

Don't use in, on or at before this, next, last and every, or before today, tomorrow and yesterday.

The weekend

British English says at the weekend; American English says on the weekend.

Common mistakes

• × in Monday → on Monday
• × on July → in July
• × in six o'clock → at six o'clock
• × at the morning → in the morning
• × on next week → next week
• × I sleep in night. → I sleep at night.