How to Calculate Hours Worked

Working out your hours by hand takes four steps: convert the times to a 24-hour clock, subtract, take out unpaid breaks, and convert to decimal hours if your payroll needs them. The trick is to do the arithmetic in minutes. Most mistakes come from treating clock times like ordinary decimal numbers.

Step 1: Write both times on a 24-hour clock

A 24-hour clock removes the AM and PM confusion. Morning times stay the same. For afternoon and evening times, add 12 to the hour.

“Minutes since midnight” is the hours times 60, plus the minutes. You don’t have to write it down, but it makes the next step easy.

Step 2: Subtract the start time from the end time

Using the example of clocking in at 8:47 AM and out at 5:12 PM:

• In minutes: 1,032 − 527 = 505 minutes.
• In hours and minutes: 505 ÷ 60 = 8 remainder 25, so 8 hours 25 minutes.

If you’d rather subtract clock times directly, borrow 60 minutes when the end minutes are smaller than the start minutes: 17:12 − 8:47 becomes 16:72 − 8:47 = 8:25.

If the end time is earlier than the start time, the shift crossed midnight. Add 24 hours to the end time first. See how to calculate overnight shift hours for examples.

Step 3: Subtract unpaid breaks

Take out only the breaks you are not paid for, usually a meal break. With a 30-minute unpaid lunch:

505 − 30 = 475 minutes, or 7 hours 55 minutes.

Under federal rules, a bona fide meal period, generally 30 minutes or more when you are fully relieved of duty, is not work time. Short rest breaks are generally paid. If your employer automatically deducts a lunch you worked through, raise it with them. More detail is in how to calculate lunch breaks on a time card.

Step 4: Convert to decimal hours if you need to

Payroll systems multiply hours by a rate, so they use decimal hours. Divide the minutes by 60:

475 ÷ 60 = 7.92 hours (rounded to two places).

Adding up a week: the 7:30 vs 7.30 mistake

The most common error is adding hours-and-minutes as if they were decimals. Here is a five-day week:

Adding the minutes column gives 2,410 minutes, which is 40 hours 10 minutes, or 40.17 decimal hours.

If you instead type 7.55 + 8.10 + 8.00 + 8.20 + 7.45 into a regular calculator, you get 39.30, and that looks like 39 and a third hours. Two errors happened at once: minutes were treated as hundredths, and the result was read back as hours and minutes. The real total is almost an hour higher. Always add minutes, or convert each day to decimal hours first.

Rounding

Some employers round clock punches to the nearest 5 minutes, tenth of an hour (6 minutes), or quarter hour. Federal rules allow this only if, over time, it does not shortchange employees for time they actually worked. If your employer rounds, round each punch the same way before you subtract. Otherwise, use exact minutes.

The fast way

The time card calculator does all four steps for a full week, including split shifts, overnight shifts, unpaid breaks, and overtime. For a quick total of a few start and end times, use the work hours calculator. To convert a single value, use the decimal hours calculator.

Sources

• 29 CFR 785.19, Meal periods (Cornell Legal Information Institute)
• 29 CFR 785.48, Use of time clocks and rounding (Cornell Legal Information Institute)