How much does time clock rounding change your hours?

Original analysis · Published 15 November 2026 · Data under CC BY 4.0

Rounding to the nearest 5, 6 or 15 minutes evens out on average, but a single week can drift. Under the 15-minute “7-minute rule”, only 6.9% of shifts kept their exact length, and 29% of five-shift weeks ended 15 minutes or more away from the time actually worked.

Key findings

• Neutral on average. Across 692,640 shifts per rule, rounding lengthened exactly as many shifts as it shortened, and the average change was zero minutes.
• Quarter-hour rounding moves single shifts the most. A shift can gain or lose up to 14 minutes, against 4 minutes for 5-minute rounding.
• Weeks drift. 95% of quarter-hour weeks were within 27 minutes of the real total, and 2.9% were 30 minutes or more away.
• Habits decide who loses. Clocking in 1–7 minutes early and out 1–7 minutes late loses 8 minutes a shift, about 34.7 hours a year on a five-day week. Rounding that always favours the employer would remove 14 minutes a shift, about 60.7 hours a year.

Results by rounding rule

Download the full distribution (CSV): for each rule, every possible error in minutes with the number and share of shifts.

How we ran the study

We took every start minute in a day, 00:00 to 23:59, and every shift length from 4 to 12 hours in one-minute steps: 692,640 shifts. For each rule we rounded the clock-in and clock-out to the nearest interval and compared the rounded length with the real one. A punch exactly halfway, possible only with 6-minute rounding at 3 minutes, rounds up.

For weekly figures we combined five shifts, each drawn independently from that per-shift distribution, and calculated the exact distribution of the weekly difference rather than sampling. The calculation code is covered by automated tests that check, for example, that 7 minutes past the hour rounds down and 8 rounds up.

When does rounding cost you time?

Nearest rounding is only neutral if punch times are spread evenly. Real punches cluster around the start and end of a shift. If you routinely clock in a few minutes before your start time and out a few minutes after your finish, nearest-quarter-hour rounding removes those minutes almost every day: 8 minutes a shift on average across the 49 early-and-late combinations we tested.

In the US, the Department of Labor’s rule on rounding, 29 CFR 785.48(b), accepts rounding to the nearest 5 minutes, tenth of an hour or quarter hour on the presumption that it averages out so employees are paid for all the time they actually work. A practice that only ever rounds against workers does not average out. This study describes arithmetic, not legal advice; for a dispute, see the official sources below.

Check your own time card

1. Get your raw punch times, not the rounded times on the pay stub.
2. Enter them in the time card calculator to get your actual worked time.
3. Compare that total with the paid hours using the payslip check. A steady gap in one direction over several periods is worth raising with payroll.

Limitations

The study treats every punch minute as equally likely and shifts as independent, which real schedules are not; the early-and-late scenario shows how clustering changes the result. It covers single continuous shifts and rounds only clock-in and clock-out, not breaks.

Sources and reuse

• 29 CFR 785.48: use of time clocks and rounding (eCFR)
• US Department of Labor Fact Sheet 22: hours worked

You may reuse the figures and data with a link to this page: “Tally My Shift, Time clock rounding study, 2026”.

Read the plain-English guide to time clock rounding