Time Calculator
Use this free time calculator to add or subtract two durations in hours, minutes, and seconds, or to convert any duration into decimal hours, total minutes, and total seconds. Carries are normalised automatically (90 minutes becomes 1 hour 30 minutes), and negative results show with a minus label so the direction is clear.
The calculator operates on durations, not calendar dates. For calendar arithmetic (days between dates, weekday lookups, business days), use the date calculator instead. For work hours with start and end times, the hours calculator is purpose-built and easier to use.
Everything you need for duration math
Six features that cover add, subtract, and convert.
Add and subtract
Combine two durations or take one away from another with normalised carry-over handling.
Convert to decimal hours
Get the same length as decimal hours, total minutes, and total seconds in one go.
Normalised output
90 minutes becomes 1 hour 30 minutes automatically. No 0h 70m results.
Negative results handled
When subtracting more than you have, the result shows with a minus sign so direction is clear.
Live as you type
Results update the moment you change any field.
Mobile-friendly layout
Clean responsive design that works on phones, tablets, and desktops.
Who uses a time calculator?
Anyone with a duration to add up.
Workout intervals
Add together a series of stopwatch readings to find total session time.
Cooking and recipes
Add prep time, cook time, and rest time to find a clean total.
Billing freelance work
Convert tracked hours-minutes-seconds to decimal hours for invoicing.
Movie marathons
Add up film runtimes plus breaks to plan a viewing block.
Music playlists
Sum track lengths to confirm a playlist fits a target duration.
Race splits
Add up lap or split times in any precision, then convert for analysis.
About durations
A clear guide to time math, decimal hours, and carry-over.
What is a duration?
A duration is a span of time without a specific start or end. It is measured in hours, minutes, and seconds, or as a single decimal hour figure. Durations behave differently from calendar dates: adding two durations is straightforward arithmetic, while adding to a date involves calendar logic. The calculator works on durations only.
How the calculator works internally
Internally, the calculator converts every duration to total seconds. Hours times 3600, plus minutes times 60, plus seconds. The math (add or subtract) is then a single subtraction or addition. The result is converted back to hours, minutes, and seconds at the end, with each unit kept under its natural maximum (60 seconds, 60 minutes).
Normalising carries
When adding 0h 45m and 0h 30m, the raw sum is 0h 75m. The calculator normalises this to 1h 15m, the way a clock would display the same duration. Similarly, 0h 0m 90s becomes 0h 1m 30s. This is what most people expect and what stopwatches and timekeeping software produce.
Decimal hours and why they matter
Decimal hours represent any duration as a single number rather than a triple. 2 hours 30 minutes is 2.5 decimal hours. 15 minutes is 0.25. 45 minutes is 0.75. Payroll, billing, and most spreadsheet math use decimal hours because multiplying by a rate is easier than multiplying by a "2:30" string. The conversion is minutes divided by 60, plus seconds divided by 3600.
Negative durations
If you subtract a larger duration from a smaller one, the result is negative. The calculator displays the absolute value with a minus label so you can see the direction. For most real-world questions (how much time is left, how long was the lap), you want the positive result; the sign indicates that you have the inputs swapped.
Time of day versus duration
"9:30 AM" is a time of day; "9 hours 30 minutes" is a duration. The two look similar but behave very differently. The time calculator works with durations only. For start-and-end-of-day questions (work shift, opening hours), use the hours calculator. For date-on-the-calendar questions, use the date calculator.
Summing a long list of durations
The calculator pairs two durations at a time. For a long list, add the first two, then use the result as the first duration in a new pair, and continue. For very long lists (say, more than 10 entries), copy each one into a spreadsheet column with decimal hours and use SUM. The math is the same.
Rounding and precision
Decimal hours and total minutes are shown with a sensible number of decimal places. The internal calculation works in whole seconds, so rounding does not introduce drift. A long chain of additions and conversions stays accurate.
When the time calculator is the right tool
Use the time calculator when you have a span of time (workout intervals, prep time, drive time, song lengths) and you want to add, subtract, or convert it. Use the hours calculator when you have specific start and end times for a work shift. Use the date calculator when you are working with calendar dates and want days, weeks, or months apart.
Frequently asked questions
If you don't find your question here, ask us directly.
It converts each duration you enter into total seconds, does the requested add or subtract on those seconds, then converts the result back into hours, minutes, and seconds. For durations alone, it shows the same length in decimal hours, total minutes, and total seconds so you can use whichever unit you need.
In add or subtract mode, enter the first duration as hours, minutes, and seconds, pick Add, then enter the second duration. The result combines them, with carries normalised: 90 minutes becomes 1 hour 30 minutes, not 0h 90m. This is how a stopwatch would naturally show the total.
Set the larger duration first, pick Subtract, then enter the second. For example, 2h 30m minus 0h 45m gives 1h 45m. If you subtract a larger duration from a smaller one, the calculator shows the absolute value with a minus label so you know which direction the result goes.
2 hours and 2.0 decimal hours are the same length. But 2 hours 30 minutes is 2.5 decimal hours, not 2.30. The conversion is minutes divided by 60. So 30 minutes is 0.5 decimal hours, 15 minutes is 0.25, and 45 minutes is 0.75. The calculator shows both formats so you can copy whichever your spreadsheet or system needs.
Payroll, billing, and most spreadsheet calculations use decimal hours because they are easier to multiply. If you bill at $50 per hour and worked 2 hours 30 minutes, the math is 50 * 2.5 = $125. Trying to multiply 50 by "2:30" causes errors in most software. Use the calculator's convert mode to get the decimal figure.
Add the first pair of durations, then use the result as the first duration in a new pair, and continue. The calculator does not store a list, but you can chain manually. For long lists, copy each result into a spreadsheet and use SUM on the decimal-hour values.
Enter the length of each film as a duration in hours and minutes. Add them together, then add break and meal time. Total time is the sum of all the durations. For three 2-hour 15-minute films with a 30-minute total break, the math is (2h 15m * 3) + 30m = 6h 45m + 30m = 7h 15m.
Carrying between minutes and seconds can introduce a one-second display if you mix decimal hours and exact seconds. Internally the calculator stores total seconds, so rounding to the nearest second can shift the visible result by one. Treat the seconds digit as approximate when you are working with decimal hours.
Yes. The result is not normalised into days. A 30-hour duration appears as 30h, not 1 day 6 hours. This matches how most stopwatches and billing systems display long durations. If you need days, divide hours by 24 manually.
The time calculator works on durations and is good for adding workout intervals, video lengths, study sessions, and so on. The hours calculator works on shift times (start and end of day) and is built for work hours and timesheets. Use whichever fits your input format.
The calculator normalises the output: 0h 1m 65s becomes 0h 2m 5s. Internally it converts everything to total seconds, then expresses the result as hours, minutes, and seconds with each unit under its natural maximum (60s, 60m). This matches how a watch face would display the same duration.
You can enter, say, 90 minutes in the minutes field, and the calculator interprets it correctly as 1 hour 30 minutes. The normalisation happens internally. The result is always displayed in normalised form, so 90 minutes becomes 1h 30m 0s in the output.
Yes. Your durations stay in your browser. Nothing is sent to a server, logged, or shared. You can use the calculator without an account and even offline once the page has loaded.
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