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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →In ordinary formal prose, write noon. It is clear and avoids the ambiguity some style guides see in “12 p.m.” Prefer “12:00 noon” only when a required house style or form calls for it; several guides consider that wording redundant. If your publication or organization specifies a format, follow it.
Why “noon” is the clearest default
At the boundary between a.m. and p.m., a numeric label can make readers pause over which half of the day you mean. Writing “noon” removes that uncertainty. Chicago’s 18th edition advises against using numbers for noon or midnight outside the 24-hour system and describes “12:00 p.m.” and “12:00 a.m.” as potentially ambiguous. Chicago Manual of Style guidance
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Other guides reach a similar practical result through their own rules: AP guidance says to spell out noon and midnight when the time matters, and the University of Illinois Chicago exempts them from its general preference for numerals when writing times. AP style guidance; UIC editorial and style guide
When to use each form
| Form | Best use | What to watch for |
|---|---|---|
| noon | Default for ordinary formal prose when the intended time is midday. | Use a more specific date or time zone when the context requires it. |
| 12 p.m. | When a controlling style guide, form, or interface requires a 12-hour numeric format. | Some authorities regard it as ambiguous at the noon boundary. |
| 12:00 noon | Only when a required style or fixed form explicitly calls for it. | Microsoft says not to use “12:00 noon”; UIC likewise advises against “12 noon.” Microsoft Style Guide; UIC editorial and style guide |
| 24-hour notation | When required by the document’s standard or more suitable for its audience, such as some international or bilingual documents. | Use the convention specified by the relevant institution or standard. |
Why style guides differ
There is no single notation mandated for every formal document. Chicago advises against numeric noon and midnight in ordinary prose, while the 2016 U.S. Government Publishing Office manual lists “12 p.m. (12 noon)” and “12 a.m. (12 midnight).” That is a documented difference between guides, not proof that every government document follows the GPO manual. GPO Style Manual (2016)
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Apply the house style, journal instructions, client requirements, or form specification first. If those leave the choice open, use “noon” in running prose. Keep the format consistent within a document, while recognizing that a table or software field may impose different formatting constraints.
How to make noon and midnight deadlines precise
“Noon” identifies midday, but appointments and deadlines can still need a date and location or time zone. Include that context when a reader could otherwise misunderstand when the time applies.
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Midnight presents an additional problem: “12:00 a.m.” alone does not establish whether the deadline falls at the start of a named date or at the end of the day before it. Chicago recommends giving both dates when needed, or using wording such as “midnight, April 12–13.” It distinguishes 2400 hours at the end of one date from 0000 hours at the start of the following date. Chicago guidance on midnight and dates
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When 24-hour notation is the better fit
For international or bilingual documents, the Government of Canada points writers toward the 24-hour system in accordance with ISO 8601 and the federal identity guidance it cites. Use the convention required by the intended audience or institution rather than assuming that a 12-hour format will be understood consistently. Government of Canada guidance on time of day
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