Calculating work hours looks easy until you have to deal with lunch breaks, odd finishing times, or a shift that ends the next morning. Then a simple calculation can become surprisingly confusing.
The good thing is that you do not need any complicated formula. Once you understand the basic method, you can calculate most work shifts in a minute or two.
1. Start With the Basic Calculation
Let us take the easiest example first. Suppose you start work at 9:00 AM and finish at 5:00 PM.
The time between 9 AM and 5 PM is 8 hours. So, if you did not take an unpaid break, your total working time is simply 8 hours.
Start: 9:00 AM
End: 5:00 PM
Break: 0 minutes
Working time: 8 hours
2. What If You Took a Lunch Break?
This is where many people make a small mistake. The time you spent at work and the time you actually worked are not always the same.
Suppose you were at work from 9:00 AM to 5:00 PM but took a one-hour unpaid lunch break.
Your total elapsed time is still 8 hours. But after removing the one-hour break, your actual working time becomes 7 hours.
9:00 AM to 5:00 PM = 8 hours
Lunch break = 1 hour
8 hours − 1 hour = 7 working hours
3. What About Hours and Minutes?
Now suppose you start at 9:00 AM and leave at 5:30 PM. In this case, your total time is 8 hours and 30 minutes.
If you also took a 60-minute lunch break, simply remove that one hour. Your actual working time becomes 7 hours 30 minutes.
Start: 9:00 AM
End: 5:30 PM
Total elapsed time: 8 hours 30 minutes
Break: 60 minutes
Net work time: 7 hours 30 minutes
4. How to Calculate an Overnight Shift
Night shifts can look confusing because the finishing time may appear smaller than the starting time.
For example, imagine you start work at 10:00 PM and finish at 6:00 AM.
The important thing to remember is that 6:00 AM belongs to the next day.
From 10 PM to midnight is 2 hours. From midnight to 6 AM is another 6 hours.
10:00 PM → 12:00 AM = 2 hours
12:00 AM → 6:00 AM = 6 hours
Total = 8 hours
If you took a 30-minute unpaid break during that shift, your net working time would be 7 hours 30 minutes.
5. 12-Hour vs 24-Hour Time
You may see working hours written in either AM/PM format or 24-hour format. They represent the same time; only the way they are written is different.
| 12-Hour Time | 24-Hour Time |
|---|---|
| 9:00 AM | 09:00 |
| 1:00 PM | 13:00 |
| 5:30 PM | 17:30 |
| 10:00 PM | 22:00 |
If you normally use AM and PM, there is no need to change the way you think about time. Just make sure you do not accidentally select AM when you mean PM.
6. How to Convert Work Hours Into Minutes
Sometimes you may need the entire duration in minutes instead of hours and minutes.
The calculation is straightforward:
For example, suppose your working time is 7 hours 30 minutes.
7 × 60 = 420 minutes
420 + 30 = 450 minutes
So 7 hours 30 minutes is the same as 450 minutes.
7. Understanding Decimal Hours
Decimal hours are commonly used in timesheets, payroll calculations and billing. This is one area where it is very easy to make a mistake.
For example, 7 hours 30 minutes is 7.5 hours, not 7.30 hours.
Why? Because an hour contains 60 minutes, not 100.
| Minutes | Decimal Hour |
|---|---|
| 15 minutes | 0.25 |
| 30 minutes | 0.50 |
| 45 minutes | 0.75 |
| 60 minutes | 1.00 |
8. Common Work-Hour Calculation Mistakes
Most incorrect results come from a few simple mistakes rather than difficult maths.
- Forgetting to subtract an unpaid lunch break
- Mixing up AM and PM
- Treating an overnight shift as if it ends on the same day
- Assuming 30 minutes means 0.30 hours
- Subtracting hours and minutes as if they were normal decimal numbers
9. A Quick Example From Start to Finish
Let us put everything together.
Suppose you started at 8:45 AM, finished at 5:15 PM and took a 45-minute lunch break.
Start: 8:45 AM
End: 5:15 PM
Elapsed time: 8 hours 30 minutes
Break: 45 minutes
Net working time: 7 hours 45 minutes
That is really all there is to it: calculate the full duration first and subtract the break afterwards.
Frequently Asked Questions
How many working hours are there from 9 AM to 5 PM?
There are 8 hours between 9:00 AM and 5:00 PM. If you take an unpaid break, subtract that break from the 8 hours to get your actual working time.
How many hours is 9 AM to 5:30 PM with a one-hour lunch?
The total elapsed time is 8 hours 30 minutes. After subtracting the one-hour lunch break, the net working time is 7 hours 30 minutes.
How long is a shift from 10 PM to 6 AM?
A shift from 10:00 PM to 6:00 AM the following morning is 8 hours before any breaks are deducted.
Is 7 hours 30 minutes the same as 7.30 hours?
No. In decimal format, 7 hours 30 minutes is 7.5 hours. The number after the decimal is a fraction of an hour, not normal minutes.
What is the easiest way to calculate work hours?
For a simple shift you can calculate the difference manually. If your shift includes breaks, minutes or crosses midnight, using a time calculator is usually quicker and reduces the chance of a small calculation mistake.
Enter your start time, end time and break duration in our free calculator. It will calculate the elapsed time and net working time for you.
Use the Time Duration Calculator →