12-hour Time Format
The 12-hour clock cycles from 1 through 12 and normally needs an AM/PM marker or enough context to distinguish morning from afternoon/evening. Human-facing style guides differ on punctuation, capitalization, and whether to write noon or midnight instead of 12:00 AM/PM.
In 12-hour time, pair the clock time with AM/PM when needed for clarity. Microsoft style writes forms such as “10:45 AM” and prefers “noon” or “midnight” over ambiguous 12:00 AM/PM.
Key details
Important caveats
Clarity Boundary
A 12-hour clock often needs AM/PM or surrounding context because the hour numbers repeat twice each day.
Noon Midnight Boundary
Microsoft advises writing “noon” and “midnight” rather than “12:00 noon,” “12:00 midnight,” or ambiguous 12:00 AM/PM forms.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- Date and time terms — Microsoft Style Guide (opens in a new tab)Microsoft · Microsoft house style for AM/PM and human-facing time notation