AM vs. PM Formatting
AM and PM distinguish the two halves of a 12-hour day, but punctuation and capitalization are style choices. Microsoft house style uses uppercase “AM” and “PM,” preceded by a space; other style guides may use forms such as “a.m.” and “p.m.”
Follow your house style. Microsoft uses uppercase “AM” and “PM” with a preceding space, as in “10:45 AM”; other styles may use “a.m.” and “p.m.”
Key details
Important caveats
Style Boundary
Do not present one publisher’s punctuation/capitalization as universal; follow the style guide governing the document.
Further guidance
Example
Microsoft-style: “The webinar begins at 3:30 PM.” A publication following another house style might write “3:30 p.m.” without changing the time itself.
Microsoft Style
Microsoft writes “AM” and “PM” in capital letters and places a space before them.
Practical Application
When using Microsoft-style time notation, place a space before uppercase “AM” or “PM,” as in “10:45 AM.” If another style uses “a.m.”/“p.m.”, apply that system consistently instead.
Reader Check
Separate the meaning decision (morning versus afternoon/evening) from the style decision (capitalization, periods, and spacing). The governing guide controls the latter.
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.