Time Calculator
Add and subtract hours, minutes and seconds. Running total mode for timesheets, or calculate the time between two clock times
Total Time
00:00:00
Decimal Hours
0.00
Total Minutes
0
Total Seconds
0
What the Time Calculator Does
Two modes. Add and subtract handles a list of time entries (hours, minutes, seconds), each with a plus or minus operator, and gives you the running total. Time between takes a start clock time and an end clock time and tells you how long elapsed, with a checkbox for cases where the period crosses midnight.
Output appears in three formats simultaneously: HH:MM:SS for clock-style display, decimal hours (5h 30m becomes 5.50) for timesheets and billing, and total minutes for sports times and music durations. The result updates as you type, so there's no calculate button to press.
Why Time Arithmetic Is Awkward
Time doesn't add cleanly because the units are mixed bases: 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day. Adding 0:45 + 0:35 = 1:20, not 0:80. The calculator does the conversion behind the scenes by translating everything into seconds, doing the arithmetic, then converting back. This avoids the off-by-one errors that creep in when people try to add times in their head.
Subtraction is where it gets really fiddly. 03:15 - 02:45 isn't '0:30 with a borrow'; you have to convert the hours into minutes first. The 'time between' mode handles this by parsing both times into total seconds since midnight, doing a straight subtraction, and adding 86,400 seconds (one full day) when the end time falls before the start time and the 'crosses midnight' option is ticked.
Common Time-Calculation Scenarios
| Scenario | Mode to use | Tip |
|---|---|---|
| Total hours worked across multiple shifts | Add/subtract | One row per shift, all with + operator |
| Subtract a 30-minute lunch break | Add/subtract | Set the operator to - on the break row |
| Time between clock-in and clock-out | Time between | Tick 'crosses midnight' if you finish next day |
| Cumulative running time of a playlist | Add/subtract | Each track length as one row |
| Race split times to total finish | Add/subtract | Use seconds field for sub-minute splits |
| Total length of a podcast series | Add/subtract | Round to nearest minute if helpful |
How Decimal Hours Work for Timesheets
Many billing and payroll systems expect time in decimal format rather than HH:MM. The conversion is simple: minutes divided by 60, then added to the hours. So 1 hour 30 minutes is 1.50 hours, 2 hours 15 minutes is 2.25 hours, 7 hours 45 minutes is 7.75 hours. The calculator shows both formats so you can copy whichever your system needs.
Decimal hours are a hangover from accounting systems that hated mixed-base arithmetic. They've stuck around because spreadsheets handle decimal numbers easily and HH:MM badly. If you're invoicing a client at £75 per hour for 2 hours 24 minutes of work, decimal makes the maths straightforward: 2.40 × £75 = £180. The [Work Hours Calculator](/work-hours-calculator) is built specifically around decimal hours plus break deductions.
Frequently Asked Questions
How do I add a list of times?
In Add/Subtract mode, leave each row's operator on the plus sign and fill in the hours and minutes (and seconds if needed). The total at the bottom updates as you type. Use the Add Row button if you need more than two entries. There's no upper limit; the calculator handles long lists fine.
Why is my result negative or zero?
If you've subtracted more time than you added, the calculator clamps the result to zero rather than showing a negative time, since negative durations rarely make practical sense. If you genuinely need a negative result (for example, calculating how much you're under a target time), do the subtraction in the opposite direction and read the result as 'how much short'.
What does 'crosses midnight' mean in time-between mode?
If your start time is, say, 22:00 and your end time is 06:00, the simple difference would be -16 hours. But if you actually mean a night shift that started at 10pm and finished at 6am the next morning, the real elapsed time is 8 hours. Tick the box and the calculator adds 24 hours to the end time before subtracting, giving the correct overnight duration.
Can I use this for billing in 6-minute or 15-minute increments?
Yes, but you'll need to round the decimal-hours result yourself. 6-minute increments correspond to 0.1 of an hour, so round up to the nearest 0.1 (a 14-minute task becomes 0.30 hours, billed). 15-minute increments correspond to 0.25 of an hour. Some legal and consultancy timesheets use either system.
How does this differ from the date difference calculator?
This one handles times within a single day or short totals across multiple sessions. The [Date Difference Calculator](/date-difference-calculator) handles intervals measured in days, months and years between two specific calendar dates. Use this for clocked time, that one for elapsed dates.
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