How the math works

How a day is calculated

Each time is read as minutes since midnight. A day's worked time is the clock-out minutes minus the clock-in minutes, then minus any unpaid break. If the break is longer than the shift, the day floors at zero rather than going negative. So 9:00 AM to 5:30 PM is 510 minutes, and a 30-minute lunch leaves 480 minutes, which is 8 hours.

Overnight shifts

When the clock-out reads earlier than the clock-in, the shift has crossed midnight, and a full day (1440 minutes) is added to the difference. 10:00 PM is 1320 minutes and 6:00 AM is 360 minutes; 360 minus 1320 is negative, so adding 1440 gives 480 minutes, which is 8 hours. This is the single rule that makes night shifts come out right.

Reading the time you type

A time with AM or PM is read as written. A time with no AM or PM is read on the 24-hour clock, so 8:00 is the morning and 20:00 is the evening. Where a field has an AM and PM control, that control is applied to plain 12-hour entries like 5, so 5 with PM becomes 17:00, but it is ignored for a clearly 24-hour entry like 1700. This keeps the common "9 to 5" from being read as a 20-hour day.

Decimal hours

Decimal hours are minutes divided by 60. Fifteen minutes is 0.25, thirty is 0.50, forty-five is 0.75. Payroll rounds to two decimal places, so seven minutes, which is 0.11666..., is shown as 0.12. The conversion chart is generated from this same rule, so the chart and the calculators never disagree.

Rounding

When rounding is turned on, each punch time is rounded to the chosen increment (5, 6, or 15 minutes), and then the span is measured, which is how a time clock does it. Nearest rounding sends a punch to the closest mark; up and down force the direction. For the quarter hour, the nearest method puts the boundary at 7.5 minutes: a punch 7 minutes or less into the quarter rounds back, and 8 or more rounds forward. That is the 7-minute rule, shown on the 7-minute rule calculator.

Weekly totals and overtime

A week is the sum of its day totals. Hours over 40 in a week are marked as overtime at time and a half, the federal rule under the Fair Labor Standards Act. On a biweekly card each week keeps its own 40-hour threshold, so the two weeks are not merged into an 80-hour total. Where a daily overtime rule applies, such as California's overtime after 8 hours and double time after 12, the engine can apply it as a separate rule without double counting hours against the weekly 40.

Gross pay

If you enter an hourly rate, the gross figure is simply the rate times the total hours, straight time. It is labeled gross on purpose: it is not overtime-adjusted pay and it is not take-home. For overtime pay and for what the hours are worth after tax, use Plain Paycheck.

It all runs in your browser

Every rule above is computed on your device. Nothing you enter is sent anywhere, which is both the privacy design and the reason the tools work offline. See the privacy page for how that is guaranteed.