Hours Calculator

Two questions that sound like one

People search for an hours calculator meaning one of two different things. The first is a span: I started at nine and stopped at half past five, how long was that. The second is arithmetic on lengths: two hours forty plus fifty five minutes minus twenty. Both are here, side by side, because trying to answer both in one clever input box mostly produces a box that guesses wrong.

The left panel takes two clock times and gives you what is between them. The right panel takes lengths of time and adds or subtracts them. Neither needs a particular format. Times can be typed as 9, 930, 9:30, 09:30 or 5:30p. Lengths can be typed as 90, 1:30 or 1h30m. Whatever you type, the result appears as you go.

Hours and minutes against decimal hours

Every result is given twice, once as hours and minutes and once as decimal hours, because those are two different units and mixing them up is the most expensive small error in timekeeping. Eight hours and fifteen minutes is 8.25 in decimal, not 8.15. Eight hours and twenty minutes is 8.33, not 8.20. The gap looks trivial on one day and stops looking trivial across a month of them.

The rule is that minutes divide by sixty. Six minutes is a tenth of an hour, which is why some payroll systems record time in six minute units: every value lands on a clean decimal. Legal and accountancy billing often uses the same tenth of an hour unit for exactly that reason. Fifteen minute quarters are the other common choice, and they give the tidy 0.25, 0.5 and 0.75 that most people already know.

If you are filling in a timesheet, check which form it wants before you write anything in it. A field labelled hours almost always wants the decimal. A field with a colon in the example wants hours and minutes.

Times that cross midnight

A span whose end time is earlier than its start is read as running into the next day. That makes 22:00 to 06:00 come out as eight hours instead of the minus sixteen a plain subtraction would give. It is the single most common failure in a homemade spreadsheet formula, and it shows up as either a negative number or an empty cell depending on how the sheet was built.

The result line says when it has made that assumption. If your span genuinely was zero minutes long, or you typed the two times the wrong way round, that note is how you notice.

Subtracting, and what it is good for

The second panel allows minus as well as plus, which turns it into a budget checker. Give it the total you have and subtract what you have already used, and the answer is what is left. A negative result is shown as a negative rather than clamped to zero, because being forty minutes over is a fact worth seeing rather than hiding.

Common uses: adding up billable blocks across a day, checking whether a set of tasks fits in the time available, working out how much of a shift is left after a series of interruptions, or totalling a set of durations that came out of somewhere else in mixed formats.

The formats it understands

For clock times: a bare number is an hour, so 9 is nine o'clock. Three or four digits without a colon are read the way a 24 hour clock is spoken, so 930 is half past nine and 1745 is quarter to six in the evening. A colon, a dot or an h all separate hours from minutes. Adding am or pm, or just a or p, switches to the 12 hour reading. Midnight is 12am or 0:00 and noon is 12pm, which is the pair worth double checking, since 12am reads to most people as midday even though it is not.

For lengths: a bare number is minutes, so 90 is an hour and a half. A colon means hours and minutes, so 1:30 is the same thing. Unit letters work too, so 1h, 30m and 1h30m are all accepted. Anything the parser cannot read is marked rather than silently treated as zero, which is the behaviour that lets a wrong total look right.

When to use the time card instead

This page answers one span at a time. If you are working out a whole week of shifts, the time card calculator is the better tool: seven rows of start, end and break, daily and weekly totals, overtime against a daily or weekly threshold, punch rounding to the nearest quarter hour or tenth, gross pay from an hourly rate, and a copy button that pastes into a spreadsheet as columns.

If what you want is to measure time as it passes rather than work it out afterwards, the stopwatch counts up with laps and splits and the timer counts down. For a time in another city rather than a length of time, use the time zone converter.