Payroll mistakes usually start with simple time math. Here is the method payroll clerks use, step by step.
1. Write each time in 24-hour format
Afternoon times get 12 added: 1:30 PM = 13:30, 5:45 PM = 17:45. Morning times stay the same. This removes AM/PM mistakes. The military time chart helps.
2. Subtract start from end
17:45 − 8:15. Minutes first: 45 − 15 = 30. Hours: 17 − 8 = 9. Result: 9 hours 30 minutes. If the end minutes are smaller, borrow an hour: 17:10 − 8:40 → 16:70 − 8:40 = 8:30.
3. Remove unpaid breaks
9:30 − 0:30 lunch = 9 hours. Under US federal rules, short breaks of 5 to 20 minutes are normally paid, and meal breaks of 30 minutes or more can be unpaid if you are fully relieved of duty.
4. Convert to decimal for payroll
Divide minutes by 60: 9 hours 20 minutes = 9 + 20/60 = 9.33 hours. The decimal hours converter has a full chart.
5. Add the week
Add the decimal hours of each day. Anything over 40 in the workweek is usually overtime for non-exempt workers.
Overnight shifts
If the shift ends after midnight, add 24 to the end time: 22:00 to 06:30 → 30:30 − 22:00 = 8 hours 30 minutes.
Worked example
| Day | In | Out | Break | Hours |
|---|---|---|---|---|
| Mon | 8:00 AM | 4:30 PM | 30 min | 8.00 |
| Tue | 8:00 AM | 5:15 PM | 30 min | 8.75 |
| Wed | 7:45 AM | 4:30 PM | 30 min | 8.25 |
| Thu | 8:00 AM | 6:00 PM | 30 min | 9.50 |
| Fri | 8:00 AM | 3:00 PM | 0 min | 7.00 |
| Total | 41.50 (1.50 overtime) |
Skip the math: the time card calculator does all of this for a full week or pay period.
Updated Oct 9, 2026.
