Calculating Work Hours: The Complete Guide
To calculate work hours: subtract clock-in from clock-out, then subtract unpaid breaks. Work in hours and minutes, borrowing 60 — not 100 — from each hour. Add every day to get the week's total in H:MM, then convert once to decimal (minutes ÷ 60) and multiply by your rate for pay.
That's the whole process in five sentences. The rest of this guide walks each step with real numbers, including the two places people almost always get it wrong: time doesn't carry at 100, and overnight shifts aren't a subtraction. If you only read one section, read the one on the base-60 trap.
Why is calculating work hours harder than it looks?
Because clock time is base 60 and calculators are base 10. When you type 8.15 + 7.45 into your phone, you get 15.60. But 8:15 + 7:45 is really 16:00 — sixteen hours flat. The two answers differ by 24 minutes, and nothing on screen tells you which one you're looking at.
The reason is that :15 doesn't mean fifteen hundredths of an hour. It means fifteen minutes, and an hour has 60 of them, so :15 is a quarter of an hour — 0.25. Every mistake in this guide traces back to that one confusion. We wrote a whole post on why 8:15 + 7:45 = 16:00 if you want the long version.
So there are really two formats in play, and they do different jobs:
| Format | Looks like | Use it to |
|---|---|---|
| H:MM | 8:15 | Record time — it matches clocks and time cards |
| Decimal | 8.25 | Calculate pay — hours × rate needs a real number |
Record in H:MM. Convert to decimal once, at the end. Mixing them mid-calculation is where money goes missing.
How do you calculate hours for one shift?
Start with a single day, clock-in to clock-out. Subtract the start time from the end time, treating hours and minutes separately, and borrow when the minutes won't subtract.
- Subtract the minutes. If the end minutes are smaller than the start minutes, borrow an hour: take 1 from the hours column and add 60 to the minutes.
- Subtract the hours. That gives the raw shift length.
- Subtract unpaid breaks. Same borrow rule applies.
Worked example. You clock in at 9:15 and out at 17:40, with no break. The minutes subtract cleanly: 40 − 15 = 25. The hours: 17 − 9 = 8. The shift is 8:25 — eight hours and twenty-five minutes.
Now with a borrow. In at 9:15, out at 18:00, with a 45-minute unpaid lunch. Raw length: 00 minus 15 won't go, so borrow — 18:00 becomes 17:60. Then 60 − 15 = 45 and 17 − 9 = 8, giving 8:45. Subtract the lunch: 8:45 − 0:45 = 8:00. You worked eight hours flat.
Notice what the borrow protects you from. On a calculator, 18.00 − 9.15 = 8.85, and 8.85 − 0.45 = 8.40. That "8.40" isn't 8:40 or 8.4 hours — it's meaningless. The correct answer is 8:00.
How do you handle an overnight shift?
Don't subtract. A shift from 22:00 to 06:00 would give you 06 − 22 = −16 hours, which is obviously wrong. The clock rolled past midnight and reset.
Split the shift at midnight and add the pieces:
- Before midnight:
24:00 − 22:00 = 2:00. - After midnight:
06:00 − 0:00 = 6:00. - Add them:
2:00 + 6:00 = 8:00. The shift is 8 hours.
Subtract any unpaid break from that total as usual — a 30-minute meal break makes it 8:00 − 0:30 = 7:30. The same split works for any shift crossing midnight: hours until midnight, plus hours after.
How do you total a full week?
Add each day's worked time in H:MM, carrying 60 minutes into the hours column whenever the minutes reach or pass 60. Here's a full week including one overnight shift.
| Day | In → Out | Raw | Break | Worked |
|---|---|---|---|---|
| Mon | 8:00 → 16:30 | 8:30 | 0:30 | 8:00 |
| Tue | 9:00 → 17:45 | 8:45 | 0:45 | 8:00 |
| Wed | 8:15 → 16:15 | 8:00 | 0:30 | 7:30 |
| Thu | 7:45 → 18:00 | 10:15 | 1:00 | 9:15 |
| Fri | 22:00 → 06:00 | 8:00 | 0:30 | 7:30 |
| Total | — | — | 3:15 | 40:15 |
Add the worked column running, so you can check yourself at each step: 8:00 + 8:00 = 16:00. Plus Wednesday: 16:00 + 7:30 = 23:30. Plus Thursday: 23:30 + 9:15 — the minutes give 30 + 15 = 45, so 32:45. Plus Friday: 32:45 + 7:30 — now the minutes are 45 + 30 = 75, which is over 60, so carry an hour and keep 15. That's 39 + 1 = 40 hours and 15 minutes: 40:15.
That carry on the last line is the whole game. Sixty minutes becomes one hour; the leftover 15 stays. Our weekly timesheet walkthrough covers this day-by-day if you want more practice.
How do you convert the total to decimal hours?
Keep the whole hours; divide the minutes by 60. Our week's 40:15 total: 15 ÷ 60 = 0.25, so it's 40.25 decimal hours.
The quarter-hours are worth memorizing, since most timesheets land on them:
| Minutes | Decimal | Common mistake |
|---|---|---|
| :15 | 0.25 | not 0.15 |
| :20 | 0.33 | not 0.20 |
| :30 | 0.50 | not 0.30 |
| :45 | 0.75 | not 0.45 |
Convert the final total once rather than each row — rounding every day to two decimals lets small errors stack up across the week. The full conversion table lives in our decimal hours for payroll guide.
How do you turn hours into pay?
Multiply the decimal hours by the hourly rate. Our week is 40.25 hours; at $24 an hour, that's 40.25 × 24 = $966.00 gross.
If overtime applies, split the total first. Forty hours at the regular rate is 40 × 24 = $960.00. The extra 0:15 is 0.25 hours, and at time-and-a-half the rate is 24 × 1.5 = $36, so 0.25 × 36 = $9.00. Gross becomes 960.00 + 9.00 = $969.00 — three dollars more than the flat calculation, from fifteen minutes.
On overtime: in the United States, non-exempt employees are generally owed a premium — often time-and-a-half — for hours over 40 in a workweek, but the specifics depend on your state, your role, and how the workweek is defined. This is general US information, not legal or tax advice. Check your local rules or your employer's policy.
What are the most common mistakes?
- Treating :15 as 0.15. The base-60 trap. Fifteen minutes is 0.25 hours.
- Subtracting across midnight. Split the shift at 00:00 and add the two pieces instead.
- Forgetting to borrow. When the minutes won't subtract, take 60 from the hours column.
- Rounding every row. Convert once at the end, not day by day.
- Missing unpaid breaks. Raw shift length isn't hours worked.
- Applying one rate to everything. Split regular from overtime hours before multiplying.
Skip the mental math
Hours adds and subtracts time in H:MM with the carries and borrows handled, totals overnight shifts without a 24-hour cap, flips the whole thing to decimal in one tap, applies your hourly rate, and exports to CSV or PDF for payroll. Free, works offline, no ads, no account or sign-in.
Frequently asked questions
How do you calculate hours worked?
Subtract clock-in from clock-out for the shift length, then subtract unpaid breaks. Work in hours and minutes, borrowing 60 from the hours column when the minutes won't subtract. 9:00 to 17:45 is 8:45; minus a 45-minute lunch, that's 8:00 worked.
How do I calculate hours for an overnight shift?
Split at midnight and add. 22:00 to 06:00 is 2:00 before midnight plus 6:00 after — 8 hours. Never subtract 22:00 from 06:00 directly; you'll get a negative number.
Why can't I add work hours on a normal calculator?
It treats 8:15 as 8.15, but :15 means fifteen minutes — a quarter hour, or 0.25. Time carries at 60, not 100. 8.15 + 7.45 = 15.60 on a calculator; the real answer is 16:00.
How do I convert work hours to decimal for payroll?
Keep the whole hours and divide the minutes by 60. 40:15 becomes 40.25, and at $24 an hour that's 40.25 × 24 = $966.00 gross.
Should a timesheet total be in hours and minutes or decimal?
Record in H:MM — that's how clocks and time cards read. Convert the final total to decimal once for payroll. Converting each row separately and rounding as you go lets errors accumulate.