A worked example: an 08:00 to 20:00 shift against an 8-hour standard
Clocking in at 08:00 and out at 20:00, with a 45-minute unpaid break, works out to 11.25 total hours. Against an 8-hour standard workday, the Overtime Hours Calculator splits that into 8 regular hours and 3.25 overtime hours — the portion of the shift that ran past the standard threshold.
The formula: regular hours capped at the standard, the rest is overtime
Regular hours = the smaller of total hours worked or the standard-hours threshold; overtime hours = total hours minus regular hours. For the 11.25-hour shift above: regular hours = min(11.25, 8) = 8, and overtime hours = 11.25 − 8 = 3.25. Whenever total hours worked falls at or under the threshold, regular hours simply equals total hours and overtime comes out to exactly 0.
A 9-hour standard day: 07:30 to 16:30 with a 30-minute break
A 07:30-to-16:30 shift with a 30-minute break comes to 8.5 total hours. Measured against a 9-hour standard, the calculator returns 8.5 regular hours and 0 overtime hours, because the entire shift fits under that higher threshold. A separate, shorter case makes the same point from the other direction: a 09:00-to-17:00 shift with a full 60-minute break totals exactly 7 hours, which — against the more common 8-hour standard — also comes out to 7 regular hours and 0 overtime, since the shift never reached the threshold at all.
Why the standard-hours threshold changes the outcome, not just the shift length
The 8.5-hour shift measured against a 9-hour standard and the 11.25-hour shift measured against an 8-hour standard land on opposite outcomes — 0 overtime versus 3.25 overtime — and the difference isn't really about which shift ran longer. It's that overtime is only ever measured against whatever standard-hours value is entered, not a fixed 8-hour rule built into the calculator. Two organizations with identical shift lengths but different standard-hours policies (say, 8 versus 9) will see genuinely different overtime totals from the exact same clock-in and clock-out times, which is why that threshold is worth setting correctly before trusting the split.