Work hours look trivial until lunch breaks, overnight shifts, and decimal payroll formats get involved. The core formula never changes, but each of those three complications has its own trap. Handle them once and every timesheet after is routine.
The core formula
Net hours = clock-out time – clock-in time – unpaid break time. Example: clock in 9:00, clock out 17:30, 30-minute unpaid lunch. Gross = 8.5 hours. Minus 0.5 = 8.0 hours net. A second example: 8:00 to 17:00 with a 60-minute lunch is 9.0 gross minus 1.0 = 8.0 net.
Only subtract unpaid breaks. Paid rest breaks, typically short breaks of 20 minutes or less under many rules, stay in paid time. If your employer pays the lunch, do not subtract it. When in doubt, check your contract or handbook: the paid-versus-unpaid distinction is a policy fact, not a maths choice.
A full week, worked out
Monday to Friday, 9:00 to 17:30 with 30-minute lunches: 8.0 hours each, 40.0 for the week. Now vary Wednesday: 9:00 to 18:00 with a 45-minute lunch. Gross 9.0 minus 0.75 = 8.25. Week total becomes 40.0 – 8.0 + 8.25 = 40.25 hours. Add Saturday 10:00 to 14:00 with no lunch: 4.0 hours. Week total 44.25 hours.
Weekly overtime usually starts after 40 hours in a workweek, so this week has 4.25 overtime hours at the overtime rate, if your rules use a weekly threshold. Some places use a daily threshold instead, which would count Wednesday’s extra 0.25 hours too. Never average across two weeks for overtime: each workweek stands alone.
Overnight shifts and decimal hours
Overnight example: 22:00 to 06:30 next day with a 30-minute break. Gross = 8.5 hours (add 24 hours when the end time is earlier than the start), minus 0.5 = 8.0 net. The midnight-crossing rule is the only special case: if end is earlier than start, add 24 hours before subtracting.
Payroll uses decimal hours: minutes / 60. 7 hours 45 minutes = 7 + 45/60 = 7.75 hours, not 7.45. Writing 7.45 understates the shift by 18 minutes. Convert each day’s minutes once at the end, not per entry, to avoid rounding drift: sum all minutes for the week, then divide by 60 once.
Timesheet checklist
Record start, end, and break length every day; do not reconstruct them from memory at week’s end. Mark days off, sick days, and holidays explicitly instead of leaving blanks, since a blank looks like a forgotten entry. Keep your own copy of the timesheet: payroll records matter for overtime disputes, and your copy is your evidence. And check rounding rules: where rounding to 15 minutes is used, it must be neutral over time, not systematically in the employer’s favour.
Part-time and compressed weeks
Compressed schedules pack full-time hours into fewer days. A 4-day week at 10 hours a day gives 40 hours, with lunch breaks handled the same way: 10.5 hours on site minus a 30-minute lunch is 10 net hours. The weekly total is unchanged; only the daily shape differs.
Overtime thresholds still apply per workweek, not per day, unless your rules say otherwise. A 10-hour day is not automatically overtime if the week totals 40. But daily overtime rules in some places do trigger after 8 hours in a day, which would make each 10-hour day carry 2 overtime hours. Check which rule governs your job before agreeing to a compressed schedule.
Try it faster with the tool
You can follow every step above by hand, but the free Work Hours Calculator — Daily & Weekly Hours with Lunch Breaks does the arithmetic for you. Enter your numbers and it gives the answer right away, so you can check your hand calculation or skip straight to the result.
Quick tips
- Net = clock-out – clock-in – unpaid breaks.
- Overnight: add 24 hours when end is earlier than start.
- Decimal hours: minutes / 60; 7:45 = 7.75, not 7.45.