Hours Calculator: How to Find the Time Between Two Times
Learn how an hours calculator finds the time between two times, including overnight shifts, unpaid lunch breaks, and decimal-hour conversion for payroll and timesheets.
How to Use an Hours Calculator to Find the Time Between Two Times
An hours calculator works out how much time passes between a start time and an end time, then gives you the answer in hours and minutes (or decimal hours for payroll). To do it by hand, convert both times to the 24-hour clock, subtract the start from the end, and convert any leftover minutes into a fraction of an hour. For example, a shift from 9:00 AM to 5:30 PM is 17:30 minus 09:00, which equals 8 hours and 30 minutes, or 8.5 hours in decimal.
That single subtraction covers most cases, but two things trip people up: shifts that cross midnight, and unpaid lunch breaks. If your end time is earlier on the clock than your start time (say, 10:00 PM to 6:00 AM), add 24 hours to the end before subtracting. If there's an unpaid break, subtract those minutes at the end. Everything below walks through both situations with worked numbers, plus how to turn the result into the decimal hours your timesheet or payroll software actually wants.
The Core Formula for Hours Between Two Times
Every duration problem reduces to the same four steps. Once you've done it a few times it becomes automatic, but writing it out keeps you from making off-by-an-hour mistakes.
- Convert to 24-hour time. Add 12 to any PM hour except 12 PM. So 1:00 PM becomes 13:00, 4:45 PM becomes 16:45, and 12:30 PM stays 12:30. Midnight (12 AM) becomes 00:00.
- Subtract the start time from the end time. Handle hours and minutes separately, borrowing 60 minutes from the hours column if the end minutes are smaller than the start minutes.
- Cross midnight if needed. If the result is negative, add 24 hours.
- Subtract any unpaid break to get worked hours.
Here's the borrowing step in practice. For 8:15 AM to 4:00 PM, the minutes don't line up (00 is less than 15), so borrow an hour: 16:00 becomes 15:60. Now subtract: 15:60 minus 08:15 equals 7 hours 45 minutes. If you'd rather skip the arithmetic entirely, the Time Calculator does all four steps the moment you type in two times, and it's free with no signup.
Adding Hours to a Start Time
The reverse question, "what time is it 6 hours and 30 minutes after 9:45 AM," uses the same logic in the opposite direction. Add the hours and minutes to the start, carry 60 minutes into an extra hour when minutes exceed 59, and roll past midnight by subtracting 24 if you go over. So 9:45 plus 6:30 is 15:75, which carries to 16:15, or 4:15 PM. This is the calculation behind "add hours" searches and it's handy for project deadlines and delivery windows.
Working Hours Between Two Times: A Reference Table
Most real schedules repeat a handful of patterns. This table shows common shifts with the raw duration, a typical unpaid lunch deduction, and the resulting paid hours in both formats. Use it as a sanity check against your own math.
| Start | End | Raw duration | Unpaid break | Paid hours (h:m) | Paid hours (decimal) |
|---|---|---|---|---|---|
| 9:00 AM | 5:00 PM | 8h 00m | 30 min | 7h 30m | 7.50 |
| 8:30 AM | 4:45 PM | 8h 15m | 60 min | 7h 15m | 7.25 |
| 7:00 AM | 3:30 PM | 8h 30m | 30 min | 8h 00m | 8.00 |
| 10:00 PM | 6:00 AM | 8h 00m | 45 min | 7h 15m | 7.25 |
| 11:30 PM | 7:15 AM | 7h 45m | 30 min | 7h 15m | 7.25 |
| 6:00 AM | 2:20 PM | 8h 20m | 20 min | 8h 00m | 8.00 |
Notice the two overnight rows: 10:00 PM to 6:00 AM and 11:30 PM to 7:15 AM. Because the end clock time is "smaller" than the start, you add 24 hours before subtracting, which is the single most common source of timesheet errors. A work hours calculator removes that risk entirely by treating the second time as belonging to the next day automatically.
Handling Overnight Shifts and Crossing Midnight
Overnight shifts deserve their own walkthrough because the "smaller end time" problem feels counterintuitive. Take a nurse working 11:00 PM to 7:30 AM. In 24-hour terms that's 23:00 to 07:30. Subtracting directly gives a negative number, which is the signal to add 24 hours to the end: 07:30 becomes 31:30. Now 31:30 minus 23:00 equals 8 hours 30 minutes. Knock off a 30-minute unpaid meal break and you have 8 hours paid, or 8.00 decimal.
The same rule covers any span that includes midnight: a late delivery driver running 9:45 PM to 2:15 AM, a security guard on 8:00 PM to 4:00 AM, or a baker starting at 3:00 AM. As long as you add 24 hours whenever the end time is numerically less than the start time, the math stays honest. If your schedule wraps across more than one day, you'll want a tool that tracks full dates rather than just clock times.
Rule of thumb: if the end time on the clock is earlier than the start time, the shift crossed midnight. Add 24 hours to the end before subtracting, and the duration comes out right every time.
Converting to Decimal Hours for Payroll
Payroll systems almost never accept "7 hours 15 minutes." They want decimal hours, because you can't multiply 7:15 by an hourly wage directly. To convert, divide the minutes by 60. Fifteen minutes is 15 ÷ 60 = 0.25, so 7:15 becomes 7.25. This is the step that costs people money when they guess, because rounding 7:15 to "7.15" instead of 7.25 understates pay by six minutes per shift.
These are the conversions worth memorizing, since they cover most rounding intervals:
- 10 minutes = 0.17 hours
- 15 minutes = 0.25 hours
- 20 minutes = 0.33 hours
- 30 minutes = 0.50 hours
- 40 minutes = 0.67 hours
- 45 minutes = 0.75 hours
- 50 minutes = 0.83 hours
Once a shift is in decimal, gross pay is simple: decimal hours multiplied by the hourly rate. A 7.25-hour shift at $18/hour is $130.50. Multiply that across a week of shifts and you have your gross. If you also need to project pay over a year or compare it against a salary, the broader set of online calculators in our hub covers wage, percentage, and date math in the same browser-based, no-signup format.
The 7-Minute Rounding Rule
Many U.S. employers round clock-ins to the nearest quarter hour using the "7-minute rule": punches 1 to 7 minutes past a quarter-hour round down, and 8 to 14 minutes round up. So a 9:06 AM clock-in rounds to 9:00, while 9:08 rounds to 9:15. This is legal under federal rules as long as it averages out fairly over time and doesn't systematically shortchange workers. Knowing the rule helps you read your own timesheet and spot when rounding consistently goes against you.
Building a Weekly Timesheet
A single shift is easy; a week is where small errors compound. The reliable method is to calculate each day's paid hours separately in decimal, then add the column. Don't add the raw "h:m" values and convert at the end, because mixing formats is exactly how 8h 45m plus 7h 30m turns into the wrong number.
| Day | Start | End | Break | Paid (decimal) |
|---|---|---|---|---|
| Monday | 8:00 AM | 4:30 PM | 30 min | 8.00 |
| Tuesday | 8:00 AM | 5:00 PM | 60 min | 8.00 |
| Wednesday | 9:00 AM | 3:15 PM | 30 min | 5.75 |
| Thursday | 8:00 AM | 4:00 PM | 30 min | 7.50 |
| Friday | 7:30 AM | 1:30 PM | 0 min | 6.00 |
| Total | 35.25 |
That 35.25 total is what goes on the invoice or into payroll. Anything over 40 in a single week is typically overtime, often paid at 1.5x. If you'd rather not maintain a spreadsheet, run each day through the time duration calculator and keep a running tally; for timing live tasks during the day, the free Online Timer records exact durations you can drop straight into the sheet.
Tracking Hours Across Days and Dates
When a project spans weeks rather than a single day, you're really counting elapsed time between two full dates, not just two clock times. That's a slightly different question, and it's where an Age Calculator style date-difference tool helps, since it counts days, weeks, and months between any two calendar dates. Pair that with your daily hour totals and you can report both "calendar duration" and "hours worked" on the same project.
Common Mistakes That Throw Off Your Hours
Most hour-calculation errors fall into a few buckets. Watch for these and your totals will hold up to scrutiny:
- Forgetting the midnight crossover. The biggest one. If the end time looks earlier than the start, add 24 hours.
- Treating minutes as decimals. 30 minutes is 0.5 hours, not 0.30. This is the single costliest mistake in payroll.
- Counting paid breaks as unpaid. In many jurisdictions short rest breaks are paid and only meal breaks are unpaid. Deduct only what your contract says.
- 12 AM versus 12 PM confusion. Noon is 12:00 PM (12:00), midnight is 12:00 AM (00:00). Mixing them flips a shift by 12 hours.
- Rounding too early. Round only the final total, not each shift, or rounding errors stack up across the week.
For deeper number-crunching, like comparing this week's hours to last week's, the guide on the percentage change formula shows how to express the difference as a clean percentage. And if you time tasks by stopwatch rather than fixed start and end times, our walkthrough of the stopwatch covers capturing precise durations.
When to Use a Tool Instead of Manual Math
Doing the arithmetic by hand is worth understanding so you can catch errors, but for anything recurring, a calculator is faster and safer. Reach for the Time Calculator when you have overnight shifts, multiple breaks, or a week of entries to add up, because those are precisely the cases where manual math goes wrong. It's browser-based, free, and needs no account, so you can bookmark it and use it whenever a timesheet is due. For one-off questions like "how long is 9:15 to 6:40," the manual subtraction in this guide is plenty.
Frequently Asked Questions
How do I calculate hours between two times?
Convert both times to the 24-hour clock, subtract the start from the end, and convert leftover minutes to a fraction of an hour. For example, 9:00 AM to 5:30 PM is 17:30 minus 09:00 = 8 hours 30 minutes, or 8.5 decimal hours. If the end time is earlier on the clock than the start, add 24 hours first.
How do I calculate hours for an overnight shift?
When a shift crosses midnight, the end time looks smaller than the start time, so add 24 hours to the end before subtracting. For 11:00 PM to 7:00 AM, treat 7:00 AM as 31:00, then subtract 23:00 to get 8 hours.
How do I convert minutes to decimal hours?
Divide the minutes by 60. Fifteen minutes is 15 ÷ 60 = 0.25, thirty minutes is 0.50, and forty-five minutes is 0.75. So 6 hours 45 minutes becomes 6.75 in decimal, which is the format payroll systems need.
How do I subtract a lunch break from my hours?
Calculate the raw duration between clock-in and clock-out first, then subtract the unpaid break in minutes. A 9:00 AM to 5:00 PM shift is 8 hours raw; deduct a 30-minute unpaid lunch and you're left with 7 hours 30 minutes, or 7.5 paid hours.
Is 12 PM noon or midnight?
12 PM is noon and 12 AM is midnight. In 24-hour terms noon is 12:00 and midnight is 00:00. Mixing the two shifts a calculation by 12 hours, so double-check AM versus PM on early-morning and lunchtime entries.
How many hours is 9 to 5?
From 9:00 AM to 5:00 PM is 8 hours of total time. After a standard 30-minute unpaid lunch that's 7.5 paid hours, and after a 60-minute lunch it's 7 paid hours. Always check whether your break is paid or unpaid before deducting it.
Can I calculate hours for a whole week at once?
Yes. Work out each day's paid hours in decimal, then add the column. For example, 8.00 + 8.00 + 5.75 + 7.50 + 6.00 = 35.25 hours for the week. Keep every figure in decimal before summing so the formats don't get mixed.
What's the best free hours calculator?
The freeseosmasher.com Time Calculator handles times between two points, overnight shifts, and break deductions in your browser with no signup. It's the fastest option when you have multiple shifts or a full timesheet to total.