AM and PM Meaning
Updated June 13, 2026
AM means the time is before noon. PM means the time is after noon. These labels make 12-hour time clear because the hour numbers repeat twice each day.
Direct answer
AM stands for ante meridiem, which means before midday. PM stands for post meridiem, which means after midday. 09:00 is 9:00 AM, and 21:00 is 9:00 PM.
When AM starts and ends
AM starts at midnight, written as 12:00 AM in 12-hour time or 00:00 in 24-hour time. It continues through the morning and ends just before noon. The last AM minute is 11:59 AM.
PM starts at noon, written as 12:00 PM in 12-hour time or 12:00 in 24-hour time. It continues through the afternoon and evening until 11:59 PM.
Common examples
Why AM and PM matter
Without AM or PM, a time such as 7:30 can mean morning or evening. Adding AM or PM removes that ambiguity. The 24-hour clock avoids the issue by using different hour values: 07:30 for morning and 19:30 for evening.
If a schedule has international readers, a 24-hour time can be clearer. If a schedule is for a U.S. audience, 12-hour time with AM/PM is often easier to read.