How to Calculate Hours Worked
The reliable method has four steps: put both times on a 24-hour clock, turn them into minutes, subtract, then turn the answer back into hours — taking unpaid breaks off before the last step. Here it is with real numbers.
Step 1 — Put both times on the 24-hour clock
AM times keep their hour (9:15 AM → 9:15), PM times add 12 (5:45 PM → 17:45), except at the edges: 12:xx AM is hour 0 (midnight) and 12:xx PM stays 12 (midday). Most hand-calculation errors are born here, at the 12s — a shift starting at 12:30 AM is 0:30, not 12:30.
Step 2 — Convert each time to minutes since midnight
Multiply the hour by 60 and add the minutes. 9:15 → 9 × 60 + 15 = 555. 17:45 → 17 × 60 + 45 = 1,065. This looks like extra work, but it is what makes step 3 bulletproof: a single subtraction, no borrowing.
Step 3 — Subtract, and handle midnight
1,065 − 555 = 510 minutes. If the subtraction would go negative — a night shift, in at 22:00 (1,320) and out at 06:30 (390) — add a full day, 1,440 minutes, to the end time first: 390 + 1,440 − 1,320 = 510 minutes again. Negative durations on a timesheet always mean an overnight span was read as same-day.
Step 4 — Subtract breaks, then convert back
Take unpaid break minutes off the minute total: 510 − 30 = 480 minutes. Convert back by dividing by 60: 480 ÷ 60 = 8 exactly, so 8 hours, written 8.00 in decimal hours. For a non-round figure like 510 minutes: 510 ÷ 60 = 8.5, which is 8 hours and (0.5 × 60) 30 minutes — 8 hours 30 minutes, 8.50 decimal. The full per-minute table is the decimal hours chart.
The other method: borrowing an hour
The school method subtracts hours and minutes separately and borrows when the minutes go negative. From 9:47 AM to 5:15 PM: the minutes, 15 − 47, will not work, so borrow one hour from the end time — 5:15 PM becomes 4:75 PM. Now 75 − 47 = 28 minutes, and 4 − 9 in the afternoon-adjusted count… which is exactly where people lose track, switching between 12-hour and 24-hour halfway. The minutes-since-midnight method exists because it cannot go wrong that way; if you borrow, borrow carefully and check the answer against 7 hours 28 minutes (the minutes method: 1,035 − 587 = 448 = 7 hours 28 minutes).
Totalling a week
Add the week's days in minutes, then convert once. Converting each day to decimal hours, rounding, and adding the decimals can drift a few hundredths of an hour across a week. The time card calculator totals minutes first for exactly this reason, and labels whatever passes 40 hours in the week — the subject of the overtime guide.
Frequently asked questions
- How do I calculate hours worked including minutes?
- Exactly as above — the minutes are never a separate problem once both times are in minutes since midnight. 9:47 to 17:15 is 448 minutes, 7 hours 28 minutes, 7.47 decimal hours.
- Do I count my lunch break as hours worked?
- Usually not, if it is an unpaid meal break where you are fully off duty. Short paid rest breaks usually do count. The line is drawn by your employer and local rules, not by arithmetic — but whichever way it falls, subtract (or don't) in step 4 and say which you did.
- What if I work two shifts in one day?
- Calculate each shift separately and add the minutes — a split shift of 4 hours and 3 hours 30 minutes is 450 minutes, 7.50 hours. The add time calculator sums a list of durations like this.
- Why does my payslip show 7.47 instead of 7:28?
- Because payroll multiplies decimal hours by your rate: 7:28 cannot be multiplied, 7.47 can (448 ÷ 60 = 7.4666…, shown as 7.47). The converter moves between the two forms.