The basic formula
Hours worked equals clock out minus clock in, minus unpaid break time. That is the entire formula. Everything else on a timecard is bookkeeping around it.
Take a 7:30 AM to 4:30 PM shift. From 7:30 to 4:30 is 9 hours. If the shift includes a 30 minute unpaid lunch, subtract 30 minutes: 8.5 hours worked. If lunch was paid, or there was no lunch break, the full 9 hours counts as work time.
A 9:00 AM to 3:00 PM shift is 6 hours elapsed. With a 30 minute unpaid lunch, the answer is 5.5 hours worked. Most timecard errors come from skipping one of these steps: forgetting the lunch subtraction, or reading 8 hours 30 minutes as 8.3 hours instead of 8.5.
Converting minutes to decimals
Payroll systems work in decimal hours, not hours and minutes, so 8 hours 45 minutes becomes 8.75. The conversion is simple: divide the minutes by 60. The four values worth memorizing are 15 minutes (0.25), 30 minutes (0.50), 45 minutes (0.75), and 60 minutes (1.00).
For everything else, the division is quick. 10 minutes is 10 divided by 60, or 0.17. 20 minutes is 0.33. 40 minutes is 0.67. A shift of 8 hours 10 minutes is 8.17 decimal hours, and 8 hours 40 minutes is 8.67.
Do not mix the two formats. Adding 8.5 (meaning 8 hours 30 minutes) to 1.75 (1 hour 45 minutes) gives 10.25 decimal hours, which is 10 hours 15 minutes. The time card calculator does this conversion automatically for every day you enter.
One more conversion worth doing in your head: dollars to cents. If your rate is $20 an hour and a day shows 8.5 hours, that is 8 times 20 ($160) plus 0.5 times 20 ($10), for $170. Checking one day's pay by hand takes five seconds and catches most entry errors before they reach the weekly total.
Subtracting breaks the right way
Only unpaid breaks get subtracted. Under federal rules, breaks of 20 minutes or less must be paid, so a paid 15 minute rest break stays in your hours. Meal periods of 30 minutes or more are unpaid only if you are fully relieved of duty.
The classic example: 9:00 AM to 5:30 PM with a 30 minute unpaid lunch. Elapsed time is 8.5 hours, minus 0.5 hours of lunch, equals 8 hours worked. Run that five days a week and the total is exactly 40 hours, which is exactly why that schedule is so common.
An 8:30 AM to 5:00 PM shift with the same 30 minute lunch works out identically: 8.5 hours elapsed minus 0.5 equals 8 hours. Different punch times, same answer. This is why checking the break subtraction matters more than memorizing any one schedule.
Overnight shifts
When a shift crosses midnight, add 12 hours to the clock out time before subtracting. A 10:00 PM to 6:00 AM shift: treat 6:00 AM as 18:00 in the math, so 18 minus 22... that gives a negative number, so instead add a full day. The simple version: hours until midnight (2) plus hours after midnight (6) equals 8 hours.
With a 30 minute unpaid meal break, that overnight shift is 7.5 hours worked. The time card calculator handles this automatically when the clock out time is earlier than the clock in time.
Adding up a full week
Add the decimal hours for each day. Five days of 8.5 hours is 42.5 hours total. Because the weekly overtime threshold is 40 hours, those extra 2.5 hours are overtime at 1.5 times the regular rate.
Weekly example: Monday 8.5, Tuesday 8.5, Wednesday 8.5, Thursday 8.5, Friday 8.5, Saturday 0, Sunday 0. Total: 42.5 hours. Regular hours: 40. Overtime hours: 2.5. At a $20 hourly rate, gross pay is 40 times 20 ($800) plus 2.5 times 30 ($75), for $875 total.
Keep a running total as the week goes on. Knowing by Friday whether you are at 40 or 44 hours tells you whether Saturday is a rest day or a time-and-a-half day, and it lets you spot an employer error before the paycheck lands.
Mistakes that corrupt the math
Reading minutes as decimals is the biggest one: 8 hours 45 minutes is 8.75, not 8.45. Next is forgetting to subtract the unpaid lunch, which inflates every day by 0.5 hours and can hide real overtime.
Rounding is another. Employers may round punches to the nearest quarter hour, but the rounding must be neutral over time. If your records show 7:53 clocked in and 7:45 on the paycheck, while every 7:07 punch also becomes 7:00, that rounding only goes one way and it costs you money. Keep your own log of actual punch times.
Finally, never average across weeks. A 45 hour week followed by a 35 hour week is 5 overtime hours, not an 80 hour flat pair. Federal law counts each fixed workweek on its own.