How to calculate work hours

Published 24 September 2026 · Approximately 7 minutes

The basic work-hours formula

For a single shift, subtract the clock-in time from the clock-out time and then subtract any unpaid break:

For example, a shift from 9:00 AM to 5:30 PM lasts 8 hours 30 minutes. After a 30-minute unpaid lunch, the paid time is 8 hours.

Step 1: Put both times in the same format

You can calculate with a 12-hour clock or a 24-hour clock, but do not mix the formats within one calculation. When using a 12-hour clock, check the AM and PM labels carefully.

• 9:00 AM becomes 09:00.
• 5:30 PM becomes 17:30.
• Midnight is 00:00 in 24-hour time.
• Noon is 12:00.

Using 24-hour time often makes manual subtraction easier because the afternoon hours do not need an AM/PM conversion.

Step 2: Subtract clock-in from clock-out

Convert both times into hours and minutes, then subtract the start from the end. If the minutes in the clock-out time are smaller than the clock-in minutes, borrow one hour, which equals 60 minutes.

Step 3: Subtract unpaid breaks

Only subtract breaks that are unpaid under the applicable workplace rules. A 45-minute unpaid break from the 8-hour-35-minute example leaves:

Do not convert 50 minutes into 0.50 hours. Clock minutes use 60 minutes per hour, while payroll decimals use hundredths. In decimal form, 7 hours 50 minutes is approximately 7.83 hours.

How to calculate an overnight shift

When clock-out is earlier than clock-in, the shift usually ends on the following day. Calculate the time from clock-in to midnight, then add the time from midnight to clock-out.

The Time Calc calculator detects this automatically whenever the end time is earlier than the start time.

Add the daily totals

Calculate every day separately before adding the week. This makes breaks, missing entries and daily overtime easier to verify. Keep the totals in minutes while adding them, then convert back to hours at the end.

Separate regular and overtime hours

Overtime rules vary by jurisdiction, employment agreement and workplace. Some rules use a daily threshold, others a weekly threshold, and some use both. Confirm which rules apply before entering a threshold.

When both daily and weekly thresholds are used, avoid counting the same minutes twice. Time Calc applies optional daily overtime first and then applies weekly overtime only to the remaining regular minutes.

Convert minutes to decimal hours

Payroll systems often display hours as decimals. Divide the minutes by 60 and add the result to the whole hours:

Use the decimal hours conversion chart for quick reference.

A simple accuracy checklist

1. Confirm every clock-in and clock-out entry.
2. Check AM/PM or use 24-hour time consistently.
3. Subtract only unpaid breaks.
4. Review overnight shifts separately.
5. Apply the correct daily and weekly overtime rules.
6. Round only if the workplace's policy allows it.
7. Compare the result with the official timekeeping or payroll record.