Quick Formula
To subtract time, convert each time to the same unit, subtract, then convert back.
Time difference = End time − Start time
Example: 5:30 PM − 9:15 AM = 8 hours 15 minutes.
How to Subtract Hours and Minutes
If the minutes in the end time are smaller than the minutes in the start time, borrow 1 hour as 60 minutes.
| Start | End | Difference |
|---|---|---|
| 9:15 AM | 5:30 PM | 8 h 15 min |
| 8:45 AM | 4:10 PM | 7 h 25 min |
| 1:20 PM | 3:05 PM | 1 h 45 min |
| 10:30 PM | 6:15 AM | 7 h 45 min |
For work shifts, subtract unpaid breaks after you find the time difference. For example, 9:00 AM to 5:30 PM is 8.5 hours; with a 30-minute lunch, paid time is 8.0 hours.
Crossing Midnight
When the end time is after midnight, add 24 hours before subtracting.
10:30 PM to 6:15 AM
- 10:30 PM = 22:30
- 6:15 AM next day = 30:15
- 30:15 − 22:30 = 7:45
This is common for night shifts, flights, sleep tracking, and countdowns.
Decimal Hours
Payroll and invoices often use decimal hours:
| Time | Decimal |
|---|---|
| 15 min | 0.25 |
| 30 min | 0.50 |
| 45 min | 0.75 |
| 1 h 15 min | 1.25 |
| 8 h 30 min | 8.50 |
For payroll-specific shifts and breaks, use the time card calculator. For simple shift math, use the hours calculator.