The rule in one line, plus the two times people get wrong
Morning times (0000–1159) match the 12-hour hour directly, so 6:30 AM is 0630. From 1 PM on, add 12: 3:45 PM is 1545. The only traps are the two twelves. Midnight, 12:00 AM, is 0000, not 1200. Noon, 12:00 PM, is 1200, not 0000. Everything else follows the add-12 rule.
Conversion table
| 12-hour | 24-hour |
|---|---|
| 12:00 AM (midnight) | 0000 |
| 1:00 AM | 0100 |
| 6:00 AM | 0600 |
| 11:00 AM | 1100 |
| 12:00 PM (noon) | 1200 |
| 1:00 PM | 1300 |
| 3:00 PM | 1500 |
| 6:00 PM | 1800 |
| 9:00 PM | 2100 |
| 11:59 PM | 2359 |
The 24-hour clock is written with no colon and no AM/PM: 1545, spoken "fifteen forty-five." A round hour like 1400 is read "fourteen hundred," never "one thousand four hundred."
Where the two twelves go wrong
The 12-hour clock starts each half-day at 12 rather than 0, so the two noon-and-midnight labels sit at opposite ends of the 24-hour scale.
Both read "12" on a 12-hour clock, but midnight is 0000 and noon is 1200 — the single most common conversion mistake.
Common questions
Is midnight 0000 or 2400?
Midnight at the start of a day is 0000. Some schedules write 2400 for midnight at the very end of a day, but 0000 is the standard and avoids confusion. Either way it reads as 12:00 AM.
Why is 12:00 PM 1200 and not 0000?
Noon is 1200 because PM means after midday, and 12 hours have passed since midnight. Midnight, 12:00 AM, is 0000 because zero hours have passed. The 12-hour clock counts from 12 instead of 0, which is what makes this pair confusing.
How do I convert PM times to 24-hour in my head?
For any afternoon or evening time, add 12 to the hour: 3 PM becomes 15, so 3:45 PM is 1545. Noon stays 12. AM times keep the same hour except 12 AM, which becomes 00.
