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.
Further guidance
Example
“The session begins at 10:45 AM and ends at noon.” This follows the documented Microsoft-style pattern while avoiding an ambiguous 12:00 label.
Practical Application
Use AM/PM when surrounding context does not already make the part of day clear. In Microsoft-style material, forms such as “10:45 AM” are preferred, while “noon” and “midnight” avoid the ambiguity of 12:00 AM/PM.
Reader Check
Before publishing a time, ask whether a reader in the intended audience could mistake morning for afternoon/evening, and whether the required house style specifies punctuation or capitalization for AM/PM.
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 · Official Microsoft house-style guidance for dates and times, including date ordering and formatting examples.