Time Duration Calculator

How to Use the Time Duration Calculator

Subtracting one clock time from another is arithmetic in base sixty, which is why people get it wrong so often and so confidently. The answer also has to be expressed twice — as hours and minutes for a human, and as decimal hours for a payroll system — and confusing the two is the most expensive mistake on a timesheet.

1. Enter the start and end times. Use the twenty-four hour clock or your device's own time picker. If the end is earlier than the start, the calculator treats it as an overnight shift and adds a day.
2. Enter any unpaid break in minutes. Most jurisdictions require an unpaid break above a certain shift length, and it comes off the paid total rather than off the time on site.
3. Read the hours-and-minutes figure for people and the decimal figure for anything that will be multiplied by a rate.
4. Check the quarter-hour rounding. Many payroll systems round to the nearest quarter, and seeing what that does to your figure is worth ten seconds.

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Time Duration Formula

Convert both times to minutes past midnight, subtract, then translate the result into whatever form is needed. Working in minutes throughout avoids every base-sixty trap.

The distinction between 7:45 and 7.75 is the whole reason this page exists. Seven hours and forty-five minutes written as 7.45 in a spreadsheet understates the shift by eighteen minutes, because minutes are sixtieths and the decimal point wants hundredths. Repeated across a five-day week that is an hour and a half.

The overnight rule is a convention rather than a deduction. A shift recorded as 22:30 to 06:15 could in principle mean minus sixteen hours, but nobody has ever meant that, so adding a day is the only sensible reading — and it is what every timesheet system does.

Example

Worked example one: 09:15 to 17:45 with a 45-minute break. The start is 9 × 60 + 15 = 555 minutes past midnight and the end is 17 × 60 + 45 = 1,065. The gross duration is 1,065 − 555 = 510 minutes, which is 8 hours 30 minutes, or 8.50 decimal hours.

Taking off the 45-minute break leaves 465 minutes: 465 ÷ 60 is 7 with 45 left over, so 7 hours 45 minutes. As a decimal that is 465 ÷ 60 = 7.75 hours — not 7.45, which is the number that ends up on timesheets and costs eighteen minutes a day.

7.75 is already an exact quarter hour, so payroll rounding changes nothing here. As a share of the day it is 465 ÷ 1,440 = 32.29%.

Worked example two: an overnight shift, 22:30 to 06:15. The start is 1,350 minutes past midnight and the end is 375. Subtracting gives −975, which is negative, so a day is added: −975 + 1,440 = 465 minutes.

That 465 minutes is the gross duration — 7 hours 45 minutes on the clock, exactly matching the day shift before its break. Keep the same 45-minute break and the paid figure becomes 465 − 45 = 420 minutes, or 7 hours even, which is what the calculator shows for these two times.

The check on the method is that both shifts produce the same gross length from the same procedure. Without the overnight rule the subtraction would have returned minus sixteen hours and fifteen minutes, a figure no payroll system has ever wanted.

Decimals for Machines, Minutes for People

Use the decimal figure wherever the number will be multiplied and the hours-and-minutes figure wherever it will be read. Rate calculations, invoices and spreadsheets all want decimals; rotas, contracts and conversations want hours and minutes. Mixing them is how eighteen minutes a day disappears.

The quarter-hour tile shows what payroll rounding does to your shift. Rounding to the nearest quarter is legal in many jurisdictions provided it is neutral over time — sometimes up, sometimes down — and it becomes a problem only when the rounding runs one way, which is worth watching across a month rather than a day.

Breaks deserve a second look because their treatment varies. An unpaid break comes off the total, as here. A paid break does not, and a break you were required to stay on site for is often legally working time regardless of what it is called. If in doubt, the test is usually whether you were free to leave.

The overnight handling is worth trusting rather than working around. Adding a day whenever the end time is not after the start is the only interpretation anyone ever means, and it makes a night shift and a day shift of the same length produce identical figures — as the two worked examples show.

For a whole week of shifts rather than one, the work hours calculator totals them, splits regular from overtime and turns the result into gross pay.

Five Things a Real Timesheet Adds

Five things that make a real timesheet differ from this arithmetic.

Rounding at each end. Some employers round clock-in and clock-out times to the nearest quarter before calculating anything, which is not the same as rounding the total. Rounding both ends can lose or add half an hour a week where rounding the total would not.

Paid against unpaid breaks. A short rest break is often paid and a meal break usually is not. The practical test in many jurisdictions is whether you were genuinely free to leave, rather than what the break is called on the rota.

Shift premiums. Night, weekend and public holiday hours frequently attract a higher rate, so two shifts of identical length are not worth the same. The duration is the input to pay, not the answer.

Where the day boundary sits. An overnight shift may count entirely towards the day it started, or be split at midnight across two days. It matters for daily overtime thresholds and for premium hours, and the rule comes from the contract rather than the clock.

Clock drift. A wall clock, a punch machine and a phone rarely agree to the minute, and a shift measured against one and recorded against another picks up an error at both ends. It is small on any single day and systematic across a month if the same clock is consistently fast.

Where it matters, agree in advance which clock is authoritative. That is a conversation worth having once rather than an argument worth having repeatedly.

Travel and handover time. Time spent travelling between sites, handing over at the end of a shift, or waiting on call is treated very differently across jurisdictions and contracts. None of it appears between a start time and an end time, and some of it is legally working time.