Calculating a work shift sounds simple: subtract the starting time from the ending time. In practice, timesheets become confusing when a shift includes an unpaid lunch, starts before noon and ends after noon, crosses midnight, or needs to be converted into decimal hours for payroll. The reliable method is to convert each time to one consistent format, find the elapsed time, subtract unpaid breaks, and only then total the week.
The basic work-hours formula
For a shift that begins and ends on the same day, use:
Hours worked = Clock-out time - Clock-in time - Unpaid breaks
Suppose you clock in at 8:15 a.m., clock out at 5:00 p.m., and take a 30-minute unpaid lunch. The elapsed time from 8:15 to 5:00 is 8 hours 45 minutes. After subtracting the break, the paid time is 8 hours 15 minutes.
Why minutes are not hundredths of an hour
One of the most common timesheet mistakes is writing 8 hours 15 minutes as 8.15 hours. A clock has 60 minutes in an hour, not 100. To convert minutes to a decimal, divide the minutes by 60:
Decimal hours = Whole hours + (minutes 60)
- 15 minutes 60 = 0.25, so 8:15 becomes 8.25 hours.
- 30 minutes 60 = 0.50, so 7:30 becomes 7.50 hours.
- 45 minutes 60 = 0.75, so 6:45 becomes 6.75 hours.
- 20 minutes 60 = 0.333..., so 8:20 is approximately 8.33 hours.
Keep the time in hours and minutes while you do the subtraction, then convert the final result to a decimal if your payroll system requires it. That prevents small rounding errors from accumulating across several shifts.
A worked example with a lunch break
Imagine a shift from 7:50 a.m. to 4:35 p.m. with a 45-minute unpaid lunch. First, find the total elapsed time. From 7:50 a.m. to 4:35 p.m. is 8 hours 45 minutes. Subtracting the 45-minute lunch leaves exactly 8 paid hours.
If there are several breaks, add the unpaid breaks together before subtracting them. For example, a 30-minute lunch plus a 15-minute unpaid break equals 45 unpaid minutes. Paid breaks should not be deducted. Whether a particular break is paid depends on workplace policy and applicable employment rules, so the calculator cannot decide that classification for you.
How to calculate an overnight shift
When a shift crosses midnight, the clock-out time appears earlier than the clock-in time. Treat the ending time as part of the next day. A convenient manual method is to split the shift at midnight.
For a shift from 10:30 p.m. to 6:45 a.m.:
- 10:30 p.m. to midnight = 1 hour 30 minutes
- Midnight to 6:45 a.m. = 6 hours 45 minutes
- Total elapsed time = 8 hours 15 minutes
If the employee also takes a 30-minute unpaid break, the paid time becomes 7 hours 45 minutes, or 7.75 decimal hours.
Using 24-hour time to avoid a.m./p.m. errors
Twenty-four-hour time makes subtraction more straightforward. Morning hours remain similar, while 1:00 p.m. through 11:59 p.m. become 13:00 through 23:59. For example, 8:15 a.m. is 08:15 and 5:00 p.m. is 17:00. The interval from 08:15 to 17:00 is clearly 8 hours 45 minutes.
For overnight work, add 24 hours to the next-day ending time before subtracting. A 22:30 start and 06:45 finish can be treated as 22:30 to 30:45. The difference is again 8 hours 15 minutes.
How to total a weekly timesheet
Calculate each day's paid time separately, then add the daily results. Consider this example:
- Monday: 8 hours 15 minutes
- Tuesday: 7 hours 50 minutes
- Wednesday: 8 hours 5 minutes
- Thursday: 8 hours 30 minutes
- Friday: 6 hours 40 minutes
Add the hours first (37) and then the minutes (140). Because 140 minutes equals 2 hours 20 minutes, the weekly total is 39 hours 20 minutes. In decimal form, 20 60 is about 0.333, producing 39.33 hours when rounded to two decimal places.
Estimating gross pay
For a single hourly rate, estimated gross pay is simply decimal hours multiplied by the hourly rate. At $20 per hour, 39.33 hours would produce approximately $786.60 before taxes and other deductions. Overtime rules, shift differentials, commissions, tips, and multiple pay rates can change the result. Use the hours total as a starting point, then apply the rules shown by the employer or payroll system.
Hours Calculator → enter multiple shifts, subtract breaks, and estimate gross pay without doing the time conversion by hand.Common mistakes to check
- Mixing a.m. and p.m., especially for noon or midnight.
- Entering 30 minutes as .30 instead of .50 decimal hours.
- Subtracting a paid break or forgetting an unpaid one.
- Rounding every shift before totaling the week.
- Forgetting that an overnight ending time belongs to the following day.
For an accurate record, compare the final total with the original clock-in and clock-out entries before submitting it. A calculator can handle the arithmetic, but the result is only as reliable as the times and break information entered.