AM and PM full form: ante meridiem and post meridiem

AM stands for ante meridiem and PM stands for post meridiem. They are Latin: ante means before, post means after, and meridiem means midday. So AM is the time before noon and PM is the time after noon.

The 12-hour clock

• AM runs from midnight to just before noon: 12:00 at night through 11:59 in the morning.
• PM runs from noon to just before midnight: 12:00 in the day through 11:59 at night.

The confusing ones: 12 AM and 12 PM

By the usual convention, 12 AM is midnight and 12 PM is noon. Many people get these the wrong way round, so for anything important, such as a ticket or an examination, it is safer to write "12 noon" or "12 midnight", or to use the 24-hour clock. A deadline of "11:59 PM on 5 March" is clearer than "12 AM on 6 March".

Changing to the 24-hour clock

For PM times from 1:00 onwards, add 12. Railway timetables in India use the 24-hour clock, so a train at 00:15 leaves a quarter of an hour after midnight, at the very start of that date.

How to write them

AM, am, A.M. and a.m. are all accepted; choose one and be consistent. Leave a space after the number: 7 AM. Do not add "in the morning" as well: "7 AM in the morning" says the same thing twice.

The other AM and PM

AM also means amplitude modulation in radio. PM also means Prime Minister.

More chat full forms

• OMG Oh My God
• TBH To Be Honest
• DM Direct Message
• PFA Please Find Attached
• TBD To Be Decided
• NA Not Applicable
• PTO Please Turn Over
• c/o care of

All chat, letters and everyday Next: RSVP explained

Check what matters. These pages explain names and terms in general. Rules, dates, fees and limits change: take them from the official body. Read on 12 November 2026.