24-hour to 12-hour time converter

24-hour and 12-hour time, side by side

This tool converts between 24-hour (military) time and 12-hour (AM/PM) time. Type a value into either input and the other updates instantly. The status line tells you whether the value you entered is valid. Below the inputs, the "now" line shows the current time in both formats.

Both formats are widely used. 24-hour time is the international standard for transit timetables, military and aviation operations, and most scientific software. 12-hour time is the conventional civilian display in the United States, Canada, the United Kingdom, Australia, and other English-speaking countries.

The edge cases

12:00 AM is midnight, the start of a new day. 12:00 PM is noon, the middle of the day. This is the most common source of confusion in 12-hour notation: people read "12 AM" as noon and get it wrong. The converter handles both correctly. In 24-hour notation, midnight is 00:00 and noon is 12:00, which is unambiguous.

Times from 00:00 to 00:59 in 24-hour map to 12:00 AM through 12:59 AM in 12-hour. Times from 12:00 to 12:59 in 24-hour map to 12:00 PM through 12:59 PM. Times from 13:00 onwards subtract 12 and become 1:00 PM through 11:59 PM.

Input formats it accepts

The 24-hour input expects HH:MM with a colon separator. Single-digit hours are accepted (9:00 parses as 09:00). The 12-hour input expects H:MM AM or H:MM PM with a space before AM/PM; case doesn't matter. Spaces inside the value are normalised. Anything else surfaces an "invalid" status without altering the other field.

For higher-precision use cases, like seconds or fractional seconds, the converter doesn't handle them, but the math is the same: append the seconds unchanged. AM/PM only affects the hour field.

When to use which format

Use 24-hour when ambiguity would be expensive: medication schedules, transit timetables, server logs, scheduled jobs, multi-timezone meetings. The format makes overnight transitions visually obvious (23:55 then 00:05 reads as wrap-around without you having to think). Use 12-hour for civilian-facing displays where the audience expects AM/PM, like restaurant opening hours or family communication.

Many digital systems internally store time in 24-hour or as a UTC timestamp and convert to 12-hour only for display. That's the right pattern: the source of truth is unambiguous; the presentation layer adapts to the audience.

A short history

The 12-hour clock predates the 24-hour clock. It's based on dividing day and night each into twelve "hours", a convention going back to ancient Egypt and inherited into Roman and medieval European timekeeping. The 24-hour clock became standard for military and railway operations in the 19th and 20th centuries, where overnight or 24-hour-shift contexts made the 12-hour format error-prone.

International Standard ISO 8601 specifies a 24-hour notation with a colon separator (HH:MM:SS), which is the format you'll see in most modern timestamps. The standard avoids AM and PM entirely.

Related tools

If you're converting times because you're scheduling across timezones, our how-long-until tool takes an arbitrary date and time and produces a live countdown that any viewer sees in their own timezone. The online timer handles fixed-duration countdowns, and the midnight countdown counts to the start of the next day.

For age and birthday calculations, the age calculator handles year-month-day arithmetic. For weekday-specific events, the weekday countdown set covers all seven days.

Privacy

The converter runs entirely in your browser. Nothing you type is uploaded, stored, or analysed. The "now" line uses your local system clock.

A short tour of related time tools

If you reached this page while converting a meeting time across timezones, the harder problem is usually the timezone offset, not the format. The format converter handles AM/PM versus 24-hour. To translate a target between timezones, encode the moment in your how-long-until URL using your audience's local time and tell them so explicitly. The countdown then reads correctly for them.

For recurring weekly events at a specific clock time, the named weekday countdowns let you set the target hour and minute in the picker. Each page is bookmarkable; the countdown resets every week.

For the start of the calendar day rather than a specific clock time, the midnight and tomorrow countdowns target the same instant with different copy.

Common conversions, worked out

Here are a few conversions that come up often. 14:30 in 24-hour is 2:30 PM in 12-hour. 09:00 is 9:00 AM. 23:59 is 11:59 PM. 00:00 is 12:00 AM (midnight). 12:00 is 12:00 PM (noon). 00:30 is 12:30 AM, half an hour past midnight. 12:30 is 12:30 PM, half an hour past noon. Notice the asymmetry around midnight and noon: the hour rolls from 12 to 1 in the 12-hour format, and the AM/PM marker shifts only at noon, not at midnight.

Common error: writing "12:30 PM" when you mean "12:30 AM" for a half-past-midnight target. The result on a calendar invite is a meeting twelve hours off. The converter on this page catches the difference because the 24-hour input is unambiguous.

AM and PM, what the letters stand for

AM is short for the Latin ante meridiem, "before midday". PM is short for post meridiem, "after midday". The convention places noon at the boundary: the hour after midnight is 12 AM through 12:59 AM, then 1:00 AM through 11:59 AM, then 12:00 PM (noon) through 12:59 PM, then 1:00 PM through 11:59 PM.

The system isn't logically tidy, midnight isn't "after midday" in any obvious sense, but it's the convention English speakers have used since the medieval period. The 24-hour clock sidesteps the awkwardness by not using the labels at all.