Full form of AM is Anti Meridiem, full form of PM is Post Meridiem or Prime Meridiem.

The short forms AM and PM derive from Latin : 

  • AM = Ante Meridiem - Before Noon
  • PM = Post Meridiem - After Noon

The 12-hour system divides the 24 hours of each day into two periods lasting 12 hours Each. The first 12-hours time period is considered as AM which runs from Midnight to Noon. The second time period is designated as PM, it covers the 12 hours from Noon to Midnight. 


The numbers from 1 to 12, followed by AM or PM, the 12-hour clock system identifies all 24 hours of the day. For example, 5 AM is early within the morning, and 5 PM is late within the afternoon.

Ante Meridiem is commonly denoted as AM, am, a.m., A.M. ; Post Meridiem is usually abbreviated as PM, pm, p.m., or P.M. All the variants are equally correct and widely used.