What this calculator does
The 24-hour clock counts straight through from 0000 to 2359 with no AM or PM, which removes the ambiguity that makes 12-hour time awkward. Military usage writes it as four digits with no colon, so half past three in the afternoon is 1530, spoken as fifteen thirty.
The two times that cause trouble are both noon and midnight. Midnight is 0000 and noon is 1200, but in 12-hour form midnight is 12:00 AM and noon is 12:00 PM, which is the reverse of what the AM and PM labels seem to suggest. The rule is that PM hours add 12 except for 12 PM itself, and 12 AM becomes 00.
The formula
Hours after noon have 12 added, so 3 PM becomes 15. 12 AM becomes 00 and 12 PM stays at 12, which are the two exceptions to the rule. The result is written as four digits with the colon dropped. Minutes since midnight is included because it is the form most useful for arithmetic on times, since it avoids carrying at sixty.
| Term | Meaning |
|---|---|
| 24-hour clock | Hours numbered 0 to 23, with no AM or PM needed. |
| Military time | The same clock written as four digits without a colon, such as 1530. |
| 0000 | Midnight at the start of the day. Some conventions write 2400 for midnight at the end of a day. |
| Minutes since midnight | The time as a single number from 0 to 1439, useful for calculating durations. |
The inputs explained
| Field | What to enter |
|---|---|
| Time | The time to convert. It is entered in 24-hour form and reported in both, so the conversion works in either direction by reading the appropriate line. |
When to use it
Reading a roster or flight schedule
Transport, healthcare and military schedules all use 24-hour time, and a misread 1800 as 8 PM rather than 6 PM is a two-hour error in the direction that makes you late.
Setting up a system that expects 24-hour input
Most software, logs and configuration files use 24-hour time, so converting from the 12-hour form people think in is a routine step.
Calculating a duration across the afternoon
Minutes since midnight makes duration arithmetic straightforward, since subtracting two of those numbers gives minutes directly with no carrying at sixty.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What do common times look like on both clocks?
Five times spanning the day, including both of the awkward ones.
| 24-hour input | Military time | 12-hour time | Minutes since midnight |
|---|---|---|---|
| 00:00 | 0000 | 12:00 AM | 0 |
| 09:15 | 0915 | 9:15 AM | 555 |
| 12:00 | 1200 | 12:00 PM | 720 |
| 15:30 | 1530 | 3:30 PM | 930 |
| 23:59 | 2359 | 11:59 PM | 1,439 |
Questions
What is 1530 in 12-hour time?
3:30 PM. Subtract 12 from any hour of 13 or above to get the PM time. 1530 minus 12 hours gives 3:30, and because the original hour was above 12 it is in the afternoon.
Is midnight 0000 or 2400?
Both conventions exist. 0000 is midnight at the start of a day and 2400 is midnight at the end of the preceding one, and they refer to the same instant. Military and ISO usage generally prefers 0000, and this calculator uses it.
Why is noon 12 PM and midnight 12 AM?
Because AM means before noon and PM after it, so noon itself is the boundary and neither label strictly applies. The convention that noon is 12 PM and midnight is 12 AM is arbitrary and widely confusing, which is the strongest argument for the 24-hour clock.
How do I say military time aloud?
Read the four digits as two pairs: 1530 is fifteen thirty, 0900 is oh nine hundred. Times on the hour take hundred, so 1400 is fourteen hundred. Leading zeros are spoken as oh.
For converting between seconds, minutes, hours and days, see the time unit converter. For a 24-hour clock reading taken from a chart in degrees and minutes, see the DMS to decimal converter.