Time Calculator

How the Time Calculator works

Adding times by hand goes wrong because time is counted in sixties. Forty minutes plus thirty minutes is one hour ten, not seventy, and a column of durations quickly turns into carrying ones in your head. Spreadsheets help only if every cell is formatted as a duration, and they silently wrap totals over 24 hours back to zero unless you choose the right format.

How the time calculator reads your sum

Write terms separated by plus or minus signs. Each term can be in any of these forms, and you can mix them in one line:

• Clock style: 1:30 is one hour thirty minutes and 1:30:15 adds fifteen seconds. Hours can go past 24, so 36:00 is a day and a half.
• Units: 2h 15m, 45m, 90s or 1d 4h. Words work too, so 2 hours 15 minutes reads the same as 2h 15m.
• Decimal hours: a plain number such as 1.5 is read as hours, so 1.5 is one hour thirty minutes and 0.25 is fifteen minutes.

Every term is turned into whole seconds before anything is added. That matters more than it sounds: adding many decimal hours such as 0.33 for twenty minutes slowly drifts, because 0.33 hours is 19 minutes 48 seconds. Working in seconds keeps the total exact however many terms you add.

Reading the results

• Total is the answer in hours, minutes and seconds. A negative total means you subtracted more than you added, and it is shown with a minus sign.
• In days appears when the total passes 24 hours, splitting it into whole days and the rest.
• Decimal hours is what payroll, invoicing and project tools usually want. 7:45 becomes 7.75.
• Total minutes and Total seconds suit video lengths, exercise logs and anything billed by the minute.
• As a clock time treats the first term as a time of day and the rest as durations, which answers questions such as "what time is it 9 hours 40 minutes after 22:15". If the result crosses midnight it says how many days on, or back, it lands.

Worked examples

A cyclist logs three rides of 1:12:40, 0:58:05 and 2:03:30. Entering 1:12:40 + 0:58:05 + 2:03:30 gives a total of 4:14:15, or 4.2375 decimal hours.

A shift starts at 22:15 and lasts 9 hours 40 minutes. Entering 22:15 + 9h 40m gives a total of 31:55:00, and the clock time reads 07:55 (+1 day), so it ends just before eight the next morning.

A video is 12:30 long and you cut 1:45 and 0:50. 12:30 - 1:45 - 0:50 would be read as hours and minutes, giving 9:55:00. If you mean minutes and seconds, write 12m 30s - 1m 45s - 50s, which gives 0:09:55.

Hours and minutes versus minutes and seconds

The one ambiguity in time arithmetic is a pair such as 12:30. On a timesheet it means twelve hours thirty minutes; on a stopwatch it often means twelve minutes thirty seconds. This calculator always reads two-part clock values as hours and minutes, and three-part values as hours, minutes and seconds. For minutes and seconds, either write 0:12:30 or use units such as 12m 30s.

Common uses

• Totalling hours worked across a week of shifts with different lengths.
• Adding lap, split or stage times in running, cycling and swimming.
• Working out the running time of a playlist, podcast series or set of video clips.
• Planning a schedule backwards from a deadline by subtracting the length of each task.
• Checking that freelance time entries add up before sending an invoice.

Tips and pitfalls

Minutes and seconds above 59 are rejected in clock-style terms, because 1:75 is almost always a typing mistake. If you really mean 75 minutes, write 75m instead. Leading signs are allowed, so -0:30 + 2:00 starts from minus half an hour.

When the sum is for pay, round only at the end. Rounding each entry to the nearest quarter hour before adding can move a weekly total by more than an hour in either direction. Use the decimal hours here as the figure to multiply by the rate, then round the money.

For frame-accurate video work, where a second is split into 24, 25 or 30 frames, use a timecode calculator instead, since this tool counts in whole and fractional seconds rather than frames.

How many hours do common sums add up to

The formula converts every entry to seconds, adds or subtracts them, then splits the total back into hours, minutes and seconds; decimal hours are the total seconds divided by 3,600. For example, three 8:15 shifts give 8:15 + 8:15 + 8:15 = 24:45:00, or 24.75 hours. Each example below was run through the calculator.

Worked sums from the time calculator

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