P.M. vs. PM Formatting
P.M. and PM are formatting alternatives, not different meanings. Chicago documents several legitimate forms and prefers lowercase “p.m.” in its own style, while other publications may choose uppercase or periodless forms.
P.M., PM, p.m., and pm all occur in established styles. Chicago prefers “p.m.”; use the form required by your house style consistently.
Key details
Important caveats
Style Boundary
Do not present P.M., PM, p.m., or pm as universally correct or incorrect; follow the required publication or house style consistently.
Further guidance
Accepted Forms
Chicago’s Q&A documents multiple legitimate forms, including lowercase with periods, lowercase without periods, and uppercase forms.
Chicago Preference
Chicago’s stated preference is lowercase “p.m.” in running text.
Practical Application
P.M., PM, p.m., and pm are formatting variants. Choose the form required by the governing style and apply it consistently throughout the document.
Reader Check
Do not “correct” a valid house-style form merely because another style prefers a different one. Check capitalization, periods, spacing, and the surrounding time format together.
Worked Example
Chicago-style example: “3:30 p.m.” A house style may instead require “3:30 PM”; consistency within that style is the key decision.
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.
- Chicago Q&A — a.m., p.m., AM, and PM (opens in a new tab)The Chicago Manual of Style / University of Chicago Press · Documents multiple legitimate a.m./p.m. formatting systems and Chicago’s preference; house style governs