The time duration calculator above measures the gap between two clock times — a start and an end within a single day, or a span that runs past midnight into the next one. Enter 09:15 and 17:40 and it returns 8 hours 25 minutes, 505 total minutes, and 8.42 decimal hours, then subtracts any unpaid break and applies whatever rounding increment your timesheet uses.
This tool works with clock times, not calendar dates. If you need the number of days between 3 March and 18 September, that is a different calculation and our date difference calculator handles it. Arb Digital keeps the two separate deliberately, because merging them produces a tool that does neither job cleanly.
What This Time Duration Calculator Does
It converts two clock times into a duration expressed four ways at once: as hours and minutes, as a raw minute count, as decimal hours, and as decimal hours after rounding. Those four representations exist because different systems demand different ones. A timesheet asks for hours and minutes. A payroll import asks for decimal hours. A billing system may round to the nearest tenth of an hour. Getting a conversion wrong between them is a quiet, recurring source of underpayment and overbilling.
The tool also handles the overnight case without asking you to flag it. If the end time is earlier than the start time — 22:30 to 06:15, say — it assumes the span crossed midnight and returns 7 hours 45 minutes rather than a negative number. The result line tells you when that assumption has been applied so you can confirm it was what you meant.
How to Use It
- Enter the start time in 24-hour or your browser's local time format. The tool reads the underlying value, so display format does not affect the result.
- Enter the end time. If it is earlier than the start time, the span is treated as crossing midnight.
- Enter any unpaid break in minutes. This is subtracted from the gross duration to give the payable figure.
- Choose a rounding increment if your timesheet or billing system rounds. Leave it on exact minutes for a true duration.
- Press Calculate to see the duration in hours and minutes, total minutes, decimal hours, and the rounded decimal figure together.
The Formula: Why Time Arithmetic Goes Wrong
The reliable method is to convert both times to minutes past midnight, subtract, and convert back. 09:15 becomes 9 × 60 + 15 = 555 minutes. 17:40 becomes 17 × 60 + 40 = 1,060 minutes. The difference is 505 minutes, which is 505 ÷ 60 = 8 hours with 25 minutes left over: 8h 25m. Subtract a 45-minute break and you have 460 minutes, or 7 hours 40 minutes.
The reason people get this wrong by hand is that they subtract the hour and minute parts separately. 17 minus 9 is 8, and 40 minus 15 is 25, which happens to give the right answer here only because 40 is larger than 15. Try 09:45 to 17:20 the same way and you get "8 hours minus 25 minutes", which is not a number anyone writes down correctly under time pressure. Converting to a single unit first removes the borrowing problem entirely.
For a span crossing midnight, add 1,440 minutes — one full day — to the end time before subtracting. 22:30 is 1,350 minutes; 06:15 the following morning is 375 + 1,440 = 1,815 minutes; the difference is 465 minutes, or 7h 45m.
Decimal Hours Are Not Hours and Minutes
This is the mistake worth spending a paragraph on because it costs real money. Decimal hours express minutes as a fraction of an hour, so 8 hours 25 minutes is 8 + 25/60 = 8.4167, usually written 8.42. It is not 8.25. Writing 8.25 records 8 hours 15 minutes, a ten-minute shortfall on a single shift. Repeated across a fortnight of shifts, that is well over an hour of unrecorded time.
Machine-readable systems avoid the ambiguity altogether by using the duration format defined in ISO 8601, where 8 hours 25 minutes is written PT8H25M and cannot be misread as a decimal. The conversion table worth memorising is short: 6 minutes is 0.1 hours, 15 minutes is 0.25, 30 minutes is 0.5, 45 minutes is 0.75. Anything else, divide by 60. If you convert between units frequently, the time converter handles hours, minutes, seconds and days as a general unit conversion.
Rounding Increments and Where They Bite
Many timesheet systems round each entry to the nearest 6, 15 or 30 minutes. Rounding is not inherently unfair — it cuts both ways on any single entry — but it stops being neutral when it is applied inconsistently. Rounding the clock-in time up and the clock-out time down on every shift produces a systematic loss that looks like rounding noise but is not.
The other subtlety is when rounding is applied. Rounding the start and end times separately, then subtracting, gives a different answer from rounding the final duration. A shift from 09:07 to 17:22 rounded to the nearest quarter hour gives 09:00 to 17:30, or 8h 30m. Rounding the actual duration of 8h 15m to the nearest quarter hour leaves it at 8h 15m — a 15-minute gap between two defensible methods. This calculator rounds the final duration, which is the more common convention. If your employer rounds the punches instead, the numbers will differ and it is worth knowing why.
Overnight Shifts, Daylight Saving, and the 25-Hour Day
Clock arithmetic assumes every day has exactly 1,440 minutes. Twice a year, in regions that observe daylight saving time, that assumption fails. On the spring transition the day is 23 hours long; on the autumn transition it is 25. An overnight shift that spans the change is genuinely one hour shorter or longer than the clock difference suggests, and that hour is a real hour of work.
This calculator computes pure clock difference and does not adjust for daylight saving, because it has no way to know which jurisdiction and which date you mean. If a shift spans a transition date, calculate the clock duration here and then add or subtract the hour manually. For work across regions rather than across a transition, the time zone converter is the right tool. The authoritative reference for how civil time is defined and disseminated is the NIST Time and Frequency Division.
When You Need a Timesheet Rather Than a Single Duration
One duration is one shift. A week of shifts is a different problem, because you need running totals, per-day breakdowns, and usually an overtime threshold. Our time card calculator handles multiple days at once, and the work hours calculator covers weekly and monthly totals. Use this page when you want one clean answer for one span, and those when you want a week.
The related but distinct case is time arithmetic: adding three hours forty-five minutes to a start time to find when something will finish. That is the opposite operation — you know a duration and want an end time, rather than knowing two times and wanting a duration. The add and subtract time calculator does that, including rollover past midnight.
Reading the Result Correctly
The headline figure is the break-adjusted duration, because that is the number most people are actually looking for when they compute a shift. The grid shows the gross duration separately so you can see what the break cost, and both the exact and rounded decimal figures so you can check which one matches what your system recorded. If the rounded and exact figures differ noticeably, the rounding increment is doing more work than you might want.
A duration of zero means the two times are identical. A duration of exactly 24 hours is not possible from two clock times alone — a start and end at the same clock time is read as a zero-length span, not a full day, because clock times carry no date information. That limitation is inherent to the input, not to the calculation, and it is another reason date spans belong in a date tool.
Arb Digital builds booking systems, shift tools and client portals where time arithmetic, rounding rules and time zones are handled properly from the start.
Web Development Services Talk to Arb DigitalCommon Mistakes to Avoid
- Writing 8h 25m as 8.25 hours — the decimal equivalent is 8.42, and the difference is ten minutes on every single shift it happens to.
- Subtracting hours and minutes separately — this fails whenever the end minutes are smaller than the start minutes, which is roughly half the time.
- Treating an overnight span as negative — 22:30 to 06:15 is 7h 45m, not minus 16 hours, and a raw subtraction gives the wrong sign.
- Rounding the punches instead of the duration — the two methods give different answers, and mixing them across a team produces totals nobody can reconcile.
- Ignoring daylight saving on overnight shifts — a shift spanning the transition is an hour shorter or longer than the clock difference shows.
Related Free Tools From Arb Digital
Use the add and subtract time calculator when you know a duration and need an end time, the time card calculator for a full week of shifts, the date difference calculator for spans measured in days rather than hours, the work hours calculator for weekly totals, and the time converter for straight unit conversion. Browse the full free online tools hub for more.
Frequently Asked Questions
It is 8 hours 25 minutes, or 505 minutes, or 8.42 decimal hours. Converting both times to minutes past midnight gives 555 and 1,060; the difference of 505 minutes divides into 8 hours with 25 minutes remaining.
Add 1,440 minutes — one full day — to the end time before subtracting. A 22:30 to 06:15 shift becomes 1,815 minus 1,350, which is 465 minutes, or 7 hours 45 minutes. The calculator applies this automatically when the end time is earlier than the start.
8.42 hours. Divide the 25 minutes by 60 to get 0.4167 and add it to the 8 whole hours. Writing it as 8.25 records 8 hours 15 minutes instead, which is ten minutes short.
This calculator subtracts the break first and rounds the result, which is the more common payroll convention. Rounding before subtracting gives a slightly different figure, so it is worth confirming which order your own system uses.
No. It works with clock times within a day or across a single midnight. For the number of days, weeks or months between two calendar dates, use the date difference calculator instead.
No, it computes the pure clock difference. A shift spanning a daylight saving transition is genuinely an hour shorter or longer than the clock times suggest, so that hour has to be added or removed manually.
Because different systems require different formats. Timesheets use hours and minutes, payroll imports use decimal hours, and billing systems often round to a fixed increment. Showing all four lets you check that the figure you enter matches the format expected.
Figures produced by this tool are planning estimates only — actual pay and billing depend on your employer's or client's own rounding rules, break policy, and overtime terms.
