Midnight in 24-Hour Time
Updated June 17, 2026
In 24-hour time, midnight is 00:00 — the first minute of a new day. It equals 12:00 AM in 12-hour time. But how you write it depends on where you are writing. Pilots write 0000Z. The military writes 0000. Some schedules use 24:00 to mark the end of a day. And in Japan, you might even see 25:00.
The short version
00:00 = midnight, start of day (ISO standard, civilian, medical). 0000 = midnight, military/aviation format, no colon. 24:00 = midnight, end of day (deadlines, schedules). All three refer to the same moment. The difference is which day they belong to and what convention you follow. See 00:00 on the full time page with nearby conversions.
The four ways to write midnight
| Format | Example | When to use | Spoken as |
|---|---|---|---|
| 00:00 | 00:00 | Civilian, medical, ISO 8601 standard | "Midnight" or "zero hundred" |
| 0000 | 0000 | Military, aviation, dispatch | "Zero hundred hours" |
| 24:00 | 24:00 | Deadlines, event end times | "Twenty-four hundred" |
| 12:00 AM | 12:00 AM | General public, US/UK everyday | "Twelve AM" or "midnight" |
How each industry writes midnight
The right format depends entirely on where you work and who will read it.
Aviation: 0000Z, always
Pilots and air traffic controllers use four digits, no colon, with a Z (Zulu) suffix meaning UTC. A flight plan filed for 0000Z means the aircraft intends to depart at midnight UTC. Aviation never uses 2400 — the clock runs from 0000 to 2359. Spoken as "zero zero zero zero Zulu" or simply "zero hundred Zulu." All times in aviation are in UTC to avoid time zone confusion across flight information regions.
Military: 0000, spoken as "zero hundred"
NATO and US military write midnight as 0000 — always four digits, no colon. On operations orders, duty rosters, and after-action reports, times run from 0000 through 2359. The spoken form is "zero hundred hours." For 0030, say "zero thirty." Informally, soldiers may say "oh-dark-thirty" for early morning times, but this is slang and never used in official communication.
Medicine and nursing: 00:00 or 0000
Hospitals use both formats — sometimes on the same shift. Electronic medical records typically use the colon format (00:00, 00:15). Paper charts often use the military format (0000, 0015). The critical rule in medicine is simple: never abbreviate midnight in a way that could be misread as noon. Never write just "12:00" without AM or PM. Never write "0:00" with a single zero. The worst-case scenario — a medication given 12 hours off schedule — is why many hospitals mandate 24-hour time for all documentation.
Programming and systems: usually 00:00:00
In code and databases, midnight is typically written as 00:00:00 (with seconds) and stored in UTC. ISO 8601 format is T00:00:00Z. In most programming languages, a day starts at 00:00:00.000 and ends at 23:59:59.999. When setting cron jobs, schedules, or API rate limits that reset at midnight, use the full ISO 8601 timestamp to avoid ambiguity across time zones.
Everyday life: use "midnight" or 00:00
For emails, calendar invites, and notes, the clearest option is the word "midnight" followed by the time zone: "The deadline is midnight EST." If you must use a numeric format, 00:00 is the international standard and works everywhere. Avoid 24:00 in everyday writing unless you specifically want to emphasize the end of a day: "Sale ends 24:00 Friday."
00:00 vs 24:00 — start or end?
Both refer to midnight, but they serve different roles:
00:00
- Start of a new day
- First minute: 00:00 through 00:01
- ISO 8601 and NATO standard
- Used by: military, aviation, hospitals, computers
- "00:00 Friday" = the very beginning of Friday
24:00
- End of a day that just finished
- Last moment before the clock resets
- Not an ISO or NATO standard
- Used by: business deadlines, events, some rail timetables
- "24:00 Friday" = the very end of Friday (same moment as 00:00 Saturday)
In practice, most organizations stick to 00:00 and avoid 24:00 entirely. If you see 24:00 on a timetable or contract, it means the same moment as 00:00 the following day — the writer chose 24:00 to clarify which day midnight belongs to.
Tip: When you need to avoid all ambiguity — for flight bookings, legal contracts, or international deadlines — use 23:59 or 00:01 instead of 00:00. A deadline of "23:59 Friday" is unmistakable. A start time of "00:01 Saturday" cannot be confused with Friday night.
The Japanese 30-hour clock — times past 24:00
Japan has a unique convention that confuses many visitors: times beyond 24:00 appear in TV schedules, bar listings, and late-night venue hours. You might see a show listed at 25:00 Monday or a club open until 27:00.
This is not a mistake. It is a scheduling trick to keep everything that happens in one "programming day" under the same date. A show airing at 25:00 Monday actually airs at 1:00 AM Tuesday, but the TV guide lists it under Monday because that is the programming day it belongs to.
| Japanese display | Actual 24-hour time | 12-hour equivalent |
|---|---|---|
| 24:00 | 00:00 (next day) | 12:00 AM |
| 25:00 | 01:00 (next day) | 1:00 AM |
| 26:00 | 02:00 (next day) | 2:00 AM |
| 27:00 | 03:00 (next day) | 3:00 AM |
| 28:00 | 04:00 (next day) | 4:00 AM |
| 29:00 | 05:00 (next day) | 5:00 AM |
This convention is unique to Japanese media and entertainment scheduling. It is not part of the international 24-hour standard and does not appear in aviation, military, or medical contexts anywhere.
Common midnight mistakes
Writing 0:00 with a single zero. Always use two digits for the hour: 00:00, never 0:00. A single zero looks like a typo and can be misread in medical or technical contexts.
Writing just "12:00" without AM or PM. In 12-hour time, 12:00 alone is ambiguous. Always add AM or PM, or use 00:00 in 24-hour format.
Assuming 2400 is the standard. It is not. ISO 8601, NATO, and most computer systems use 00:00. Only use 24:00 if you specifically need to mark the end of a day.
Confusing which day midnight belongs to. 00:00 Friday is the very beginning of Friday — the minute after 23:59 Thursday. If you mean the end of Friday, say "midnight at the end of Friday" or write 24:00 Friday. Better yet, use 23:59 Friday.