Payroll systems convert every timesheet to decimal hours because pay is multiplication: rate × hours needs a single decimal number, and “8 hours 30 minutes” isn’t one. Divide minutes by 60 and the clock time becomes math-ready: 8:30 → 8.50.
The conversion in one rule
Decimal hours = hours + (minutes ÷ 60)
| Clock (h:mm) | Calculation | Decimal |
|---|---|---|
| 7:15 | 15 ÷ 60 | 7.25 |
| 7:40 | 40 ÷ 60 | 7.67 |
| 8:06 | 6 ÷ 60 | 8.10 |
| 8:30 | 30 ÷ 60 | 8.50 |
| 9:50 | 50 ÷ 60 | 9.83 |
The minute-by-minute version (1–60) lives on the decimal hours calculator, which also converts in both directions live.
The mistake that costs real money
Writing 8 hours 30 minutes as 8.30 undercounts by 12 minutes a day — 8.30 decimal hours is 8 hours 18 minutes. Across a 5-day week that’s an hour of unpaid time; at $18/hour, about $47/month. If you hand-type timesheet totals into payroll, this single digit slip is the most likely source of quiet underpayment.
The reverse error happens too: typing a decimal like 7.5 into a field expecting h:mm (7:50 ≠ 7.5 hours).
Where rounding fits
Two layers of rounding appear in real payroll:
- Punch rounding — many clocks round each day to the nearest 15 minutes (the “7/8-minute rule”: 7 min down, 8 min up) or to 6-minute tenths. Federal guidance (29 CFR 785.48) tolerates rounding only when it’s neutral over time — systematically rounding down is a wage violation.
- Decimal rounding — the conversion itself is usually kept to two decimals (8:20 → 8.33). The residue is ±18 seconds at worst; it should wash out across days.
If your employer rounds, your stub will show quarter-hour decimals only: .00, .25, .50, .75. Seeing .33 or .67 means they pay to the minute.
Doing payroll by hand? Use this pipeline
- Total each day in h:mm (end − start − unpaid breaks).
- Sum the week in h:mm, carrying 60 minutes → 1 hour.
- Convert once, at the end: total minutes ÷ 60, round to 2 decimals.
- Multiply by the rate (overtime hours at 1.5×).
Converting once at the end avoids accumulating per-day rounding. Or skip the pipeline: the time card calculator shows every day in both notations and totals the week in decimals exactly this way.