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Date & Time
Time Duration Calculator — Add & Subtract Hours, Minutes, Seconds
Duration arithmetic for timesheets, workouts, cooking, video and project tracking
A time duration calculator does the everyday math that a regular calculator gets wrong: adding and subtracting lengths of time written as hours, minutes and seconds. The trouble is that time isn't base-10. Sixty seconds roll over into a minute and sixty minutes roll over into an hour, so 45 minutes plus 45 minutes is not "90" — it's 1 hour 30 minutes. Punch those numbers into a normal calculator and you get nonsense. This tool handles the carries for you.
The method is simple once you keep the columns separate. Convert each duration to a single base unit — total seconds — do the arithmetic there, then convert back into hours, minutes and seconds:
- Total seconds = (hours × 3600) + (minutes × 60) + seconds
- Add or subtract the two totals in seconds
- Convert back: hours = total ÷ 3600, minutes = remainder ÷ 60, seconds = what's left
A quick check the way most people verify it by hand: 2h 45m + 1h 30m = 4h 15m. Add the minutes (45 + 30 = 75), carry the extra 60 into the hours (1h 15m), then add the hours (2 + 1 + 1 = 4) to land on 4 hours 15 minutes. The same routine works in reverse for subtraction — when you run short of minutes or seconds, you borrow 60 from the next column up.
This comes up constantly in American daily life. An hourly worker adding up shift segments — 3h 50m in the morning plus 4h 40m after lunch — needs the real total (8h 30m) to get paid correctly. A runner stacks mile splits to find total race time. A cook adds prep time to bake time. A video editor sums clip lengths against a target runtime. A freelancer rolls up tracked sessions for an invoice. A parent figures out how much screen time is left in the day.
The calculator also does the conversion people forget they need: a duration as total minutes, total seconds, or decimal hours. That last one matters because payroll, billing and spreadsheets almost always want decimal hours, not h:m:s. The conversion is just minutes ÷ 60: 4h 15m = 255 minutes = 15,300 seconds = 4.25 hours. That 4.25 is the number you type into a timesheet, not "4.15."
One important distinction: this tool does duration arithmetic — it adds and subtracts lengths of time. If you instead want the gap between two clock times (say 9:15 AM to 5:45 PM), use the Hours Calculator, which is built for clock-to-clock spans. Here, everything is a duration.
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Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Total seconds = hours × 3600 + minutes × 60 + seconds • Add: total = secondsA + secondsB • Subtract: total = secondsA − secondsB • Convert back: H = ⌊total / 3600⌋, M = ⌊(total mod 3600) / 60⌋, S = total mod 60 • Decimal hours = total seconds / 3600 • Total minutes = total seconds / 60
📰 Formula
• Total seconds = hours × 3600 + minutes × 60 + seconds • Add: total = secondsA + secondsB • Subtract: total = secondsA − secondsB • Convert back: H = ⌊total / 3600⌋, M = ⌊(total mod 3600) / 60⌋, S = total mod 60 • Decimal hours = total seconds / 3600 • Total minutes = total seconds / 60
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Treating time as base-10 — adding 45 + 45 minutes to get "90" instead of carrying to 1h 30m.
- Writing decimal hours as the raw minute count: 4h 15m is 4.25 hours, not 4.15 hours.
- Forgetting to borrow when subtracting — you take 60 from the next column up, not 100.
- Mixing up duration math with clock times; for a span between two times of day, use the Hours Calculator.
- Dropping the seconds column when the inputs include seconds, which throws off precise totals.
💡 Tips
- Convert everything to total seconds first, do the math, then convert back — it removes every carry-and-borrow mistake.
- For payroll or invoices, use the decimal-hours output (minutes ÷ 60), not the h:m:s form.
- Leave a field blank or zero if you don't need it — you can add hours and minutes without touching seconds.
- To total more than two durations, chain them: take this result and add the next duration to it.
Embed this calculator on your site
Copy the code below and paste it into the HTML of your site or blog.
<iframe src="https://www.calcnimbus.com/embed/time-duration-calculator" width="100%" height="500" frameborder="0" style="border:1px solid #eee;border-radius:12px"></iframe>
❓ Frequently asked questions
How do I add hours and minutes together?
Add the minutes, carry every 60 minutes into the hours column, then add the hours. Example: 2h 45m + 1h 30m → 75 minutes = 1h 15m, plus 2 + 1 hours = 4h 15m.
What is 2 hours 45 minutes plus 1 hour 30 minutes?
It's 4 hours 15 minutes. The 45 and 30 minutes add to 75 minutes, which is 1 hour 15 minutes, so you carry 1 hour over to get 4h 15m.
How many minutes is 4 hours 15 minutes?
255 minutes. Multiply the hours by 60 (4 × 60 = 240) and add the minutes (240 + 15 = 255). In seconds that's 15,300.
How do I convert hours and minutes to decimal hours?
Divide the minutes by 60 and add to the hours. 4h 15m = 4 + 15/60 = 4.25 hours. This is the format payroll and timesheets usually want.
How do I subtract one duration from another?
Subtract column by column, borrowing 60 from the next unit up when you run short. 8h 0m − 2h 45m: borrow an hour to get 7h 60m, then 60 − 45 = 15 minutes and 7 − 2 = 5 hours = 5h 15m.
Why does my regular calculator give the wrong answer for time?
A standard calculator works in base-10, but time uses base-60 for minutes and seconds. Adding 1.45 + 1.30 gives 2.75, which isn't how 1h 45m + 1h 30m works — that's 3h 15m.
Can I add seconds, not just hours and minutes?
Yes. Enter hours, minutes and seconds for each duration. Seconds carry into minutes at 60, exactly like minutes carry into hours.
What's the difference between this and an hours calculator?
This adds and subtracts durations (lengths of time). An hours calculator finds the span between two clock times, like 9:15 AM to 5:45 PM. Use whichever matches your inputs.
How do I add up more than two durations?
Calculate the first two, then take that total and add the next duration, and so on. Working in total seconds throughout keeps the carries correct.