Time Calculator
Add or subtract two durations in hours, minutes, and seconds. See the result in h:m:s as well as total minutes and seconds.
Duration 1
Duration 2
Add or subtract two durations. A negative result means duration 2 was larger than duration 1.
How to use this calculator
Enter Duration 1 and Duration 2 in hours, minutes, and seconds using the respective fields. Choose Add to sum the two durations or Subtract to find the difference. The result appears in h:m:s format as well as the total in minutes and seconds — useful when downstream systems need a single number. You can leave the seconds field as zero if your inputs are whole minutes.
Duration arithmetic vs. clock time arithmetic
It is important to understand the difference between two types of time calculation:
- Duration arithmetic (this calculator) adds or subtracts lengths of time — for example, "2 hours 30 minutes plus 1 hour 45 minutes." There is no clock face involved. The inputs could represent anything: video lengths, workout segments, project time logs, cooking times, or race splits.
- Clock time arithmetic adds a duration to a specific time of day — for example, "if I start at 9:00 AM and work for 2 hours 30 minutes, when do I finish?" For that, use the hours calculator, which takes start and end times from the clock.
Both are "time calculations," but they answer different questions. This tool is for the first type.
How time arithmetic works (base-60)
Ordinary arithmetic is base-10: digits go 0–9 and then carry over to the next column. Time is base-60 for seconds and minutes: once a unit reaches 60, it rolls over to the next unit. This makes manual time addition error-prone. The safest approach — and what this calculator uses — is to convert everything to the smallest unit (seconds) first, perform ordinary arithmetic in seconds, then convert back.
Total seconds = (hours × 3,600) + (minutes × 60) + seconds
The result in seconds is then divided by 3,600 to extract hours, the remainder is divided by 60 to extract minutes, and the final remainder is the seconds. This eliminates all carrying errors.
Worked examples
Adding durations: video editing
You have three video clips: 0:45:20, 1:12:08, and 0:33:55. Add the first two:
- 0:45:20 = 2,720 seconds
- 1:12:08 = 4,328 seconds
- Sum: 7,048 seconds = 1 hour, 57 minutes, 28 seconds (1:57:28)
Then add the third clip: 7,048 + 2,035 (0:33:55) = 9,083 seconds = 2:31:23 total runtime.
Subtracting durations: remaining time
A task is budgeted for 3:00:00 (3 hours). You have already spent 1:45:30. Subtract: 3:00:00 − 1:45:30 = 10,800 − 6,330 = 4,470 seconds = 1:14:30 remaining.
Classic example
2h 30m plus 1h 45m: 9,000 + 6,300 = 15,300 seconds = 4h 15m, or 255 minutes, or 15,300 seconds.
How to interpret your result
The h:m:s output is what you would read on a stopwatch or include in a schedule. Total minutes is useful when a system needs a single numeric value — for example, entering duration into a project management tool that accepts minutes. Total seconds is relevant for programming, scientific applications, and video production where frame-accurate timing matters.
A negative result from subtraction means Duration 2 was larger than Duration 1. The displayed negative value shows how much longer Duration 2 is — for example, if you had 1:00:00 budgeted and spent 1:15:30, the result of −0:15:30 tells you the task ran 15 minutes and 30 seconds over budget.
Common mistakes to avoid
- Treating h:m:s as decimal. 1:30 is 1 hour 30 minutes (1.5 hours), not 1.3 hours. Never multiply 1:30 by a rate as if it were 1.3 — the result will be wrong. Convert to decimal first if you need to multiply.
- Carrying manually and making base-60 errors. Adding 45 minutes + 35 minutes by hand and writing "1:20" is correct, but it's easy to make mistakes with larger numbers. Let the calculator handle the carrying.
- Using this tool when you mean clock times. If you want to know "what time is it when I finish?" rather than "how long is the total duration?" — that's a different calculation. Use the hours calculator.
- Leaving out seconds when precision matters. For video timestamps, race splits, or billing by the minute, the seconds field can change the result meaningfully. Don't round to whole minutes if precision is needed.
For clock-in/out hours worked, see the hours calculator. For weekly time cards with overtime, see the time card calculator.
How we calculate this
Each duration is converted to total seconds (hours × 3,600 + minutes × 60 + seconds). Addition sums the two totals; subtraction finds the signed difference. The result is converted back to h:m:s by integer division and modulo operations. Negative results indicate that Duration 2 exceeds Duration 1.
Frequently asked questions
How do I add two durations together?
Enter each duration in the hours, minutes, and seconds fields, then select Add. The calculator converts both to total seconds, sums them, and converts back to h:m:s. It also shows the total in minutes and in seconds for convenience.
How do I subtract one duration from another?
Select Subtract, enter both durations, and the calculator finds the difference. If Duration 2 is larger than Duration 1, the result is displayed as a negative duration — meaning Duration 1 is shorter by that amount.
Can I use this to total my work hours?
This calculator adds or subtracts two durations (lengths of time), not clock-in/clock-out times. To calculate hours worked in a single shift (from a start time to an end time), use the hours calculator. To total an entire week with overtime, use the time card calculator.
How many seconds are in an hour?
There are 3,600 seconds in an hour (60 minutes × 60 seconds). There are 86,400 seconds in a day. The calculator converts all inputs to seconds before performing arithmetic, which avoids carrying errors from base-60 addition by hand.
What is the difference between a duration and a clock time?
A duration is a length of time — 2 hours 30 minutes — with no reference to the clock face. A clock time is a specific point in the day — 2:30 PM. This calculator adds and subtracts durations. To find the time on the clock after adding a duration to a start time, use the date or hours calculator.
What if I need to add more than two durations?
Add the first two durations and note the result, then add the result to a third duration, and so on. For totalling multiple daily time entries across a week, the time card calculator is a better fit — it handles up to seven daily entries in one place.
Why does adding minutes sometimes carry over into hours?
Because time is base-60 rather than base-10. Once minutes reach 60, they roll over into a new hour. The calculator handles this automatically: 45 minutes + 30 minutes = 75 minutes, which becomes 1 hour and 15 minutes in the output.
Can this calculator handle seconds?
Yes. Each duration has a seconds field. The calculator works in seconds internally, so 1:59:59 + 0:00:01 correctly gives 2:00:00. Seconds are useful for video editing timestamps, athletic race splits, and scientific timing.