In

Use ‘in’ with months, years and periods of time such as decades or centuries:

• in January
• in 1978
• in the twenties

When does the school year begin in your country? – In mine it begins IN September.

Use ‘in’ a period of time in the future to express that an action will occur after that amount of time:

• in a few weeks
• in a couple of days

At

Use ‘at’ with an exact time:

• at six o’clock
• at 10.30
• at two p.m.

When do you eat lunch? – I usually eat it AT noon.

On

Use ‘on’ with days of the week:

• on Monday
• on Fridays

Use ‘on’ with specific calendar days:

• on Christmas day
• on October 22nd

When is your birthday? – Mine is ON October 12.

Important notes

in the morning / afternoon / evening – at night

We say in the morning, afternoon or evening BUT we say ‘at night’.