Time duration calculator

How many hours is 9:00 AM to 5:30 PM?

Eight and a half hours — 8 h 30 m, or 8.50 in decimal hours. Both times fall on the same day, so it is a plain subtraction: 17:30 minus 9:00. The minutes are the part people get wrong. 17:30 − 9:00 is 8 hours and 30 minutes, which is 8.5 hours, not 8.30 hours. Minutes are sixtieths, not hundredths.

If half an hour of that was an unpaid lunch, the paid duration is 8 h 00 m. A duration calculator measures the span; whether the whole span is paid or billable is a separate decision, and it is the one that decides what goes on the invoice.

How many hours is 10 PM to 6 AM?

Eight hours. Subtracting straight across gives 6:00 − 22:00 = −16 hours, which is the classic overnight mistake. The end time belongs to the next day, so add 24 hours to it first: (6:00 + 24 h) − 22:00 = 8 h 00 m. The calculator above does this automatically whenever the end time is earlier in the day than the start, so a night shift needs no special handling.

How do you calculate a duration across two dates?

Count the whole days between the dates, multiply by 24 hours, then add the difference between the two clock times. A job that starts at 08:00 on 3 March and finishes at 12:15 on 5 March spans two whole days — 48 hours — plus 4 h 15 m between 08:00 and 12:15. That is 52 h 15 m, or 52.25 hours, or 3,135 minutes. Fill both date fields above and it is worked out for you.

One thing worth knowing: the days are counted on the calendar, not on the clock. A span that crosses a daylight-saving change is still counted as whole calendar days, which is how payroll and timesheets treat it too.

Which unit should you actually use?

Keep minutes underneath and convert at the end. Hours and minutes are readable but base-60, so they are painful to add: a column of 1:20, 0:35 and 2:50 does not sum without carrying. Decimal hours multiply cleanly against a rate but hide the original figure. Total minutes are exact and never round. The safe habit is to hold every entry in whole minutes, add them up, and convert once — at the line that goes on the invoice.

Converting is one division: hours to decimal hours divides the minutes by 60. What that decimal is worth at your rate is what the billable hours calculator answers.

Durations are what a billable entry is made of

Every line on an hourly invoice is a duration with a name on it. The arithmetic on this page is the easy half. The hard half is remembering the spans: the twenty minutes on a client call before the meeting officially started, the file you reopened after dinner, the fix you shipped on a Sunday. Those spans are real work and they are the ones that never make it onto a timesheet, because writing them down means interrupting them.

That is the gap this calculator cannot close, and it is worth being straight about: no amount of clock arithmetic recovers a span nobody wrote down.