Time Calculator

Base sixty, not base ten

Sixty minutes to the hour means the carry happens at sixty, not at a hundred. Add 7:45 and 8:30 the way you would add decimals and you get 15:75, which is not a time. The minutes have to roll over: seventy-five minutes is one hour and fifteen, so the answer is 16:15.

This page sidesteps the problem by converting every line to seconds, adding those, and converting back. No carrying, so no carrying mistakes. The per-line table shows what each entry was understood to mean, which is the part worth checking — a typo is far more likely than an arithmetic slip.

1:30 and 1.5 are the same amount of time and different numbers

Clocks write an hour and a half as 1:30. Payroll systems and spreadsheets write it as 1.5. Mixing the two is how 1:30 becomes 1.30 and everyone loses eighteen minutes.

The conversion is minutes divided by sixty. Fifteen minutes is 0.25, twenty minutes is 0.33, forty-five is 0.75. The small table at the bottom of the results covers the values that come up most. If you are keying hours into a spreadsheet, the decimal column is the one to copy; if you are writing a schedule for a person to read, use the hours-and-minutes form.

Shifts that cross midnight

A shift from 10:30 PM to 7:10 AM subtracts to a negative number if you take the clock times at face value. The end is earlier in the day than the start, so 24 hours have to be added back. The page does that automatically and labels the end as falling on the next day.

The one thing it cannot know is whether a shift is a genuine overnight or a data entry error. A 9:00 AM start with a 5:00 AM end will be treated as a twenty-hour shift rather than flagged, because twenty-hour shifts do exist. Read the "next day" label as a check on your own input.

Note also that a shift crossing a daylight saving boundary is one hour longer or shorter in real elapsed time than the clock difference suggests. Clock arithmetic cannot see that; it is a payroll policy question and the two US transitions are in March and November.

Break time, and two ways to subtract it

There are two ways to take an unpaid break out. In the duration list, put it on its own line with a leading minus — a line reading -0:30 subtracts thirty minutes from the total. In the start-and-end section, use the break field. Both arrive at the same number; the list is better for a week of shifts, the field is better for one day.

Whether a break is unpaid at all depends on its length and your jurisdiction, and short rest breaks are usually compensable while a genuine meal break usually is not. That is a rules question, not an arithmetic one — this page subtracts what you tell it to.

What the parser accepts

Colon form: 7:30 and 1:30:45. Letter form: 1h 45m, 2.5h, 90m, 45s, and the spelled-out versions like 2 hours 15 minutes. A bare number is read as minutes, so 90 is an hour and a half. A leading minus subtracts the line. Anything it cannot read is listed rather than silently dropped, because a silently dropped line is a wrong total that looks right.

Related pages

To split a fixed block of time across a list of items instead of totalling it, use the Duration Splitter. For the number of days rather than hours between two points, see the Date Calculator. A running log of work sessions with dates attached belongs in the Work Time Log Tally.

Questions people ask