How the time duration calculator works
You give it two moments; it gives you the exact stretch of time between them, once as a human-readable breakdown (days, hours, minutes) and once as a total in every unit you might need. The date part rides on the calendar itself, so month lengths and leap years are handled without you counting on your fingers across February. Leave the times blank and it counts whole days, midnight to midnight, and says so. Enter the end before the start and it quietly measures the other way and tells you it did, because a duration is a distance and distance does not go negative.
The borrow and carry of time arithmetic
Every clock time is really a minute number: hours × 60 + minutes. So 9:30 AM is minute 570 of its day, and 2:15 PM is minute 855. Once both moments are a day count plus a minute number, the subtraction is grade-school column arithmetic, except the columns carry at 60 and 24 instead of 10.
The interesting case is the borrow. Say you left at 11:30 PM (minute 1,410) and got back at 1:15 AM the next day (minute 75). You cannot take 1,410 from 75, so you borrow one day, which is worth 1,440 minutes: 75 + 1,440 − 1,410 = 105 minutes, and the day column drops by one. Carry 105 minutes back into hours (105 ÷ 60 = 1 remainder 45) and you get 1 hour, 45 minutes. That borrow step is where nearly every by-hand mistake lives, which is why the calculator shows it with your actual numbers every time it happens.
One duration, five rulers
The same span reads differently depending on the unit, and different jobs want different units: payroll wants decimal hours, project plans want days or weeks, timers and APIs want seconds. The conversion chain is fixed:
| Unit | Equals |
|---|---|
| 1 minute | 60 seconds |
| 1 hour | 60 minutes, or 3,600 seconds |
| 1 day | 24 hours, or 1,440 minutes, or 86,400 seconds |
| 1 week | 7 days, or 168 hours, or 10,080 minutes |
Months are deliberately missing: at 28 to 31 days each, a month is not a fixed ruler, so this page totals in the units that are. If you want a months-and-days style answer for a pure date span, the date calculator does that breakdown.
Worked example
January 15, 2026 at 9:30 AM to July 19, 2026 at 2:15 PM.
Convert the times: 9:30 AM is minute 570 of its day (9 × 60 + 30) and 2:15 PM is minute 855 (14 × 60 + 15). The calendar says July 19 is 185 days after January 15 in 2026 (February has 28 days that year; the calendar handles it). Subtract the minutes: 855 − 570 = 285, no borrow needed. Carry: 285 ÷ 60 = 4 remainder 45. Answer: 185 days, 4 hours, 45 minutes.
Totals from total minutes: 185 × 1,440 + 285 = 266,685 minutes, which is 4,444.75 hours, 185.1979 days, 26.4568 weeks, or 16,001,100 seconds.
The honest note about time zones and DST
This calculator reads both moments as local clock time and does no time zone math at all. That is the right behavior for almost everything people use it for, but it has one known blind spot: daylight saving time. A span that crosses a spring-forward night is really one hour shorter than the clock arithmetic says, and a fall-back night one hour longer. For a fasting window or a project span, nobody cares. For billing a precise overnight shift on the changeover night, care. And nobody should schedule surgery by it. If your two moments live in different time zones (a flight, a call across an ocean), convert both to one zone first, then enter them; feeding it a departure in local Tokyo time and an arrival in local Denver time gives you a number that means nothing.
What people actually use this for
How long was I actually gone: enter when you left and when you got back, and settle it with minutes. Project spans: kickoff to launch, in days for the retro and weeks for the slide. How long until: today to the wedding, the deadline, the release date. Fasting windows: last bite to first bite, checked against the 16 hours you were aiming for. Flight-free travel: a train-and-ferry itinerary is a chain of local clock times, and this adds up what the journey really cost you.
If your span is really a question about a person's age, the age calculator speaks years and months. If it is a paid shift, the work hours calculator subtracts breaks and multiplies by your rate, and the time card calculator does the whole week. For pure date-to-date counting with weekday and weekend splits, use the date calculator.