Is Midnight 0000 or 2400? Both, and Here Is the Difference

A duty roster ends at midnight and the form offers no guidance on how to write it. Is midnight 0000 or 2400? The honest answer is that both are correct notations for the same instant, and they differ only in which day they attach that instant to. 0000 opens a day; 2400 closes the one before. Everything else about this question, including several long-running arguments in payroll departments, follows from that single distinction.

This article explains what each notation means, which one United States military practice prefers, why 2359 keeps appearing as a compromise, and how to write a period that ends at midnight so that nobody can misread it afterwards. The full 24-hour conversion chart shows where both sit relative to the rest of the day.

Is Midnight 0000 or 2400?

It is both, depending on which day you mean. 0000 is the first minute of a new date and 2400 is the final boundary of the previous one, and the two label the identical moment on the clock. The choice is a statement about the calendar, not about the time.

Put another way, the two forms describe the same instant written from opposite sides of the join. If you are recording when something started, the opening form paired with the new date is natural. If you are recording when a period finished, 2400 with the old date says so more clearly. Problems arise only when the date is left off, at which point neither notation can rescue the reader.

What Each Notation Actually Says

The two forms carry different implications, and the difference is worth stating plainly:

• 0000: the opening minute of a day. An entry timed this way belongs to the date written beside it, and the day then runs forward through 0001, 0002 and so on.
• 2400: the closing instant of a day. Nothing can be timed 2401, because the next tick belongs to the following date.
• 2359: the last minute that is unarguably inside the day. Widely used to end periods precisely because it needs no explanation.
• 1200: included here because it is the other point people misremember. Noon is 1200, sits exactly halfway through, and has no competing notation at all.

The international standard ISO 8601 recognises both midnight forms, permitting 24:00 as the end of a calendar day and treating it as the same instant as 00:00 on the day following. It also makes clear that 00:00 is the preferred form for a point in time. That is the same conclusion most working organisations reach on their own.

Which Does the US Military Prefer?

United States practice favours 0000. The military day is generally described as running from 0000 through to 2359, so midnight belongs to the day beginning rather than the day ending, and it is written alongside the new date.

The reason is the same one that produced the four-digit format in the first place: an entry should be readable by someone who has no idea what was intended. A midnight timestamp with a date attached leaves nothing to interpretation. 2400 still appears, particularly when a duty period, an exercise window or an authorisation is being closed, because in those cases the writer genuinely wants the boundary attached to the day being closed. Both usages are correct; neither is a mistake to be corrected in someone else paperwork. Anyone new to the four-digit form will find the underlying structure explained in how to read military time, and the reasoning behind the whole notation in why the military uses 24-hour time.

Writing a Period That Ends at Midnight

Attach a date to both ends and the ambiguity disappears entirely. A shift written as 1600 Tuesday to 0000 Wednesday can be read only one way, and so can a window written as 0800 to 2400 on the ninth of the month.

Where a date cannot be attached, ending at 2359 is the standard workaround. Contracts, permits, competition entry deadlines and system access windows routinely close at 2359 for this reason, sacrificing one minute in exchange for a boundary nobody can dispute. The equivalent habit in 12-hour writing is the familiar 11:59 PM on legal documents, which exists for precisely the same purpose. A third approach, used where the exact instant matters, is to state the boundary as a moment between two named dates rather than as a clock reading at all.

Where 0000 or 2400 Turns Up in Practice

The choice matters most wherever a record crosses the date line of an ordinary day. Night shifts, incident logs, transport schedules and clinical charts all have to decide where midnight goes before the first entry is made rather than afterwards.

Hospitals almost always open the day at midnight and close the previous one at 2359, because a medication administration record is counted per calendar day and an entry filed against the wrong date corrupts that count. Dispatch logs follow the same convention so that an incident spanning midnight reads in order. Railway timetables avoid the problem by scheduling around it, with late services shown as 2358 or 0002 rather than at midnight itself, and by printing the day of operation beside any service that crosses over. Timesheet software normally records night shifts as two entries split at midnight, which is why the hours occasionally appear to be assigned to the wrong day when the underlying dates are not displayed. In each case the fix is the same: attach the date, and prefer the notation that makes the date obvious.

Why the Question Arises at All

Midnight is the only moment on the clock that belongs to two days at once, and no notation can change that. Every other instant sits comfortably inside a single date; the boundary itself sits on the join, which is why two perfectly reasonable conventions grew up around it.

The 12-hour clock handles the same join no better. Twelve at night and twelve at midday share a number and are distinguished only by a suffix that people reverse constantly, which is why so many contracts abandon the attempt and write eleven fifty-nine at night instead. The four-digit format at least makes the two readings visibly different, so a reader who sees a boundary written one way can tell at a glance which day the writer had in mind. The one thing no notation can supply is the date, and that is the piece most often left off. If the surrounding entries in a log run in sequence, the reader can usually infer it; if the entry stands alone on a form, they cannot. The hour-by-hour military time chart shows where the boundary falls relative to the rest of the day, which helps while the convention is still unfamiliar.

Conclusion

Is midnight 0000 or 2400? Both, and the question is really about which day you want the instant to belong to. 0000 opens a day and is the form United States military practice prefers; 2400 closes the day before and is at home in contracts and duty periods; 2359 sidesteps the argument at the cost of one minute. Attach a date and none of it can go wrong. See where midnight sits on the full military time chart, watch the boundary pass on the live 24-hour clock, or read further on militarytime.now.