What is the difference between AM and PM?

The difference between AM and PM is that “a.m.” refers to the hours from noon to midnight, and “p.m.” refers to the hours from midnight to noon.

 

For example, 12:01 a.m. is the minute after midnight, and 11:59 a.m. is the minute before noon. Use the abbreviation “a.m.” after the first 12 hours of each calendar day. Use the abbreviation “p.m.” after the hours in the second half of each day. 

The abbreviations “a.m.” and “p.m.” are usually written in lowercase with periods. QuillBot’s free Grammar Checker can help you format expressions of time correctly in your writing.