Time Calculator: Add & Subtract Hours, Minutes, Seconds
A free time calculator that adds and subtracts durations like 1:30:00 + 0:45:00 - 0:10:00 across multiple rows, with automatic carrying between seconds, minutes and hours. Handy for timesheet totals and stacking recipe times.
What Is Time Calculation
Time calculation means adding and subtracting quantities of time, such as one hour thirty minutes or forty-five minutes. Typing straight into an ordinary calculator tends to produce "1.30" for "1 hour 30 minutes," which gives the wrong answer, because time runs on base 60 rather than base 10 — sixty minutes carry over into a new hour, and the carrying works completely differently from decimal arithmetic. This tool keeps hours, minutes and seconds as separate fields, so you never have to think about that conversion yourself.
Because it accepts multiple rows, you can stack up individual entries for a day's worth of work, or subtract break time from a total, all in one pass. Anything over sixty minutes or seconds carries automatically into the unit above, and subtraction that would otherwise go negative borrows correctly from the next unit up. All of the arithmetic happens right in your browser, so nothing you type is ever sent to a server.
How to Use the Time Calculator
- Enter the first duration in row one Type hours, minutes and seconds separated by colons, like "1:30:00". Minutes-and-seconds-only entries like "90:00", or minutes-only entries like "45", both work too.
- Add rows and pick a sign for each Use "Add row" to bring in more durations, and choose + or - on each row to decide whether it adds to or subtracts from the running total. Set break time to minus.
- Read the total as it updates The total refreshes as you type. Carrying and borrowing across the 60-minute and 60-second boundaries happen automatically, so there is no need to convert minutes into hours by hand partway through.
Tips for getting more out of it
- Both notations are supported: kanji-style like "1時間30分" and colon-separated like "1:30:00".
- Add as many rows as you need to sum multiple durations. Pick "-" for rows you want to subtract, such as break time.
- A negative total is shown with a leading minus sign, like "-0:15:00", and highlighted in a different color for clarity.
- Click "Load sample" to instantly see a worked example (1h30m + 45m - 10m).
- An entry with 60 or more minutes or seconds is treated as an invalid format and excluded from the total.
Where This Time Calculator Helps
Timesheet and overtime totals
Subtract break time from time on the clock to get actual hours worked. Stack a row per day and the same total doubles as a weekly or monthly sum.
Billable work-hour tracking
Freelancers and hourly professionals can add up the time spent on each piece of a job to get an accurate total before multiplying by an hourly rate.
Cooking and prep time budgeting
Add prep, cook and rest time to find the total time a recipe needs, or work backwards from a serving time to figure out when to start.
Video and audio clip duration totals
Add up the length of multiple clips or tracks to get a combined running time. Second-level precision makes it useful for fine-tuning an edit.
Workout and study time accumulation
Add up daily training or study sessions to see a weekly total, or enter a target as a negative row to see how far off you are.
Glossary
- Base 60 (sexagesimal)
- A counting system where units carry over at sixty rather than ten: sixty seconds make a minute, sixty minutes make an hour. Typing a decimal like "1.5" into an ordinary calculator to mean "an hour and a half" gives the wrong answer for exactly this reason.
- Carrying and borrowing
- Carrying is what happens in addition when seconds or minutes add up past 60 and a unit gets pushed up to the next level; borrowing is the reverse, taking 60 from the unit above when subtraction would otherwise go negative. This tool handles both automatically.
- Duration
- A value representing a length of time, like "1 hour 30 minutes," as opposed to a specific point in time such as "January 1, 2026." It is treated as the difference between two moments, or as a running sum of time spent on something.
- Unix time (epoch seconds)
- A way of representing a moment in time as a count of seconds since midnight on January 1, 1970. Internally, this tool converts every value you enter into total seconds first, does the addition or subtraction there, and only converts back to hours-minutes-seconds at the end, which avoids rounding drift from repeated carrying.
- HH:MM:SS format
- A notation for a duration written as hours, minutes and seconds separated by colons. This tool accepts both this format, like "1:30:00," and plain-language phrasing like "1 hour 30 minutes."
Frequently Asked Questions
Side Note — Why time still runs on base 60, not base 10
While most measurements — meters, currency — settled on base 10, time still runs on base 60: 60 seconds to a minute, 60 minutes to an hour. This convention traces back to ancient Babylonian mathematics, where 60 was prized because it divides evenly by 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30, making fraction arithmetic far easier with the tools available at the time.
During the French Revolution, in 1793, France briefly adopted decimal time: 10 hours per day, 100 minutes per hour, 100 seconds per minute. It was logically elegant, but the cost of rebuilding every clock and the mismatch with astronomical calculations meant it never caught on with the public, and it was formally abandoned within a few years, remembered today only as a historical curiosity.
In computing, by contrast, timestamps are almost always converted into decimal "Unix time" (a plain count of seconds) before any arithmetic happens. This tool works the same way internally: every duration you enter is first converted into total seconds, added or subtracted with its sign applied, and only converted back into the familiar base-60 display at the very end, which avoids rounding drift from repeated carrying.