Time Duration Calculator
"It felt like it lasted forever" isn't a unit of measurement. Find out exactly how long something actually took, midnight crossings and all.
Your duration will appear here.
What does a time duration calculator actually do?
A time duration calculator finds the exact gap between a start time and an end time, expressed in hours, minutes, and seconds rather than a rough guess. That sounds like basic subtraction, and mathematically it is, but clock time doesn't subtract the way normal numbers do. Minutes reset at 60, hours reset at 24, and any duration that slips past midnight adds a whole extra layer most people forget to account for until the math comes out negative.
This tool handles both the everyday version of that question โ how long was my shift, how long did the movie run, how long until the flight lands โ and the multi-day version, where the start and end aren't even on the same date. Whichever one you need, the borrowing, carrying, and midnight-crossing logic happens automatically instead of on a napkin.
How to calculate time duration by hand
Manual time subtraction comes down to three rules. First, convert both times to 24-hour format โ for PM hours, add 12, so 4:55 PM becomes 16:55. Second, subtract the start time from the end time, hours from hours and minutes from minutes. Third, if the start time's minutes are larger than the end time's minutes, borrow 60 minutes from the hours column, the same way you'd borrow 10 in ordinary subtraction, just with a base of 60 instead of 10.
For example, 8:13 AM to 4:55 PM becomes 16:55 minus 8:13. Since 55 is bigger than 13, no borrowing is needed: the answer is 8 hours and 42 minutes. But 8:13 AM to 4:07 PM becomes 16:07 minus 8:13, and since 7 minutes is less than 13 minutes, you'd borrow an hour, turning it into 15:67 minus 8:13, for a final answer of 7 hours and 54 minutes. It's easy to see how this gets error-prone fast once seconds, AM/PM, or an overnight span get added to the mix.
Overnight spans: where most manual math falls apart
A duration that crosses midnight needs one more step: a full day, 24 hours, gets added to the end time before subtracting, since the end technically happened on the following calendar day even though only a clock time was given. Skip this step and a duration like 10 PM to 6 AM comes out as a nonsensical negative number instead of the correct 8 hours. Checking "ends the next day" in Clock Time mode above handles this automatically โ no manual day-column bookkeeping required.
Clock time vs. full date and time: which mode do you need?
Clock Time mode is built for same-day and overnight questions โ a work shift, a flight, a movie, anything where the start and end both happen within roughly 24 hours of each other. Full Date & Time mode is for anything longer: a multi-day event, a rotation that spans a full week, or any stretch where the calendar date itself matters, not just the clock time. If you're not sure which one fits, ask whether the date could change between your start and end โ if yes, use Full Date & Time mode.
If what you actually need is a simple day count rather than an hour-and-minute-level answer โ say, how many calendar days sit between two dates regardless of the time of day โ the days between dates calculator is the more direct tool for that specific question.
Turning a duration into a percentage of your day
Once you know exactly how long something lasted, a natural next question is how much of your day, week, or shift it actually ate up. An 8-hour workday and a 45-minute commute both sound like "a while," but they occupy very different shares of your 24 hours. The time percentage calculator takes the duration you just found here and converts it into a percentage, which is often a more useful way to compare two very different-sized chunks of time against each other.
Time Duration Calculator FAQs
How do I calculate the duration between two times?
Convert both times to 24-hour format, then subtract the start time from the end time. If the minutes or seconds in the start time are larger than in the end time, borrow 60 from the next column over, the same way you'd borrow in ordinary subtraction. This calculator does that borrowing automatically, so you can skip straight to the answer.
How does this calculator handle a duration that crosses midnight?
Check the "ends the next day" box whenever your end time is earlier in the clock than your start time, like 10 p.m. to 6 a.m. That tells the calculator to treat the end time as belonging to the following day, adding a full 24 hours before subtracting, so an overnight shift or a late movie doesn't come back as a negative or nonsensical duration.
What's the difference between clock time mode and full date and time mode?
Clock time mode compares two times of day, like 9:00 to 17:30, and is built for same-day or overnight spans. Full date and time mode compares two complete timestamps, each with its own date, which is what you need when the gap could stretch across several days, weeks, or longer, such as timing a multi-day event or a long shift rotation.
Can I calculate a duration that spans several days?
Yes, that's exactly what full date and time mode is for. Enter a start date and time and an end date and time, and the calculator returns the total gap broken into days, hours, minutes, and seconds, plus the same total expressed as a single decimal hour figure if that's more useful for what you're doing.
How is time duration different from counting days between two dates?
Counting days between dates answers a calendar question โ how many days sit between March 1st and March 15th โ without caring about the time of day. Time duration answers a clock question, down to the hour, minute, and second, which matters when the exact start and end times change the answer, not just the dates. If you only need the calendar-day count, the days between dates calculator is the more direct tool.
Why does my duration show 0 hours when I expected a full day?
This usually happens when the start and end times are identical and "ends the next day" isn't checked, which correctly returns a zero-length duration rather than assuming a full 24 hours passed. If you actually meant exactly one full day later, check the next-day box, or switch to full date and time mode and set the end date one day ahead.
Does this calculator work with 12-hour AM/PM time?
Yes. Enter times using the hour, minute, and AM/PM fields exactly as you'd say them out loud, and the calculator converts everything to 24-hour format behind the scenes before doing the math, so you never have to do that conversion by hand.
What's a quick way to sanity-check a time duration by hand?
Round both times to the nearest easy number first. If a shift runs from roughly 9 to roughly 5, that's about 8 hours, so your exact answer should land close to that. If the calculator's precise result is wildly different from your rough estimate, double-check that AM/PM, the next-day box, and the dates (in full date and time mode) are all set the way you intended.
This tool is for educational purposes only. Always verify important results with a qualified professional.
