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Calculate time duration between two times

This free time duration calculator finds the elapsed time between any two clock times in hours, minutes, and seconds — then converts the result to decimal hours and total minutes so it's ready for billing, timesheets, or logs. Enter a start time and end time, click 'Now' to use the current time, and the result updates instantly. No account needed, nothing uploaded.

The calculator is overnight-aware: if the end time is earlier than the start, it automatically adds 24 hours and labels the result as an overnight shift. A night shift from 22:00 to 06:30 returns 8 h 30 min, not a negative number. That's a calculation step timeanddate.com leaves to you.

The time duration formula

The underlying math converts both times to minutes from midnight: total_minutes = hours × 60 + minutes. Subtract start from end. If the result is negative, add 1,440 (the number of minutes in a day). Finally, split back: hours = floor(diff / 60), minutes = diff % 60.

For example, 9:15 AM to 2:45 PM: 14 × 60 + 45 = 885; 9 × 60 + 15 = 555; 885 − 555 = 330 minutes = 5 h 30 min (5.5 decimal hours). The tool handles all of this automatically, including seconds precision and midnight crossings.

Add or subtract a duration from a time

The Add / Subtract tab lets you move forward or backward from any starting time. Enter a base time — say 14:00 — choose + or −, then specify a duration in hours and minutes. Need to know when a 1 h 45 min meeting that starts at 14:00 ends? The result is 15:45. Planning a wake-up 7 h 30 min after going to bed at 23:00? The result wraps past midnight to 06:30.

This mode is useful for deadlines, cooking timers, scheduling meetings, and calculating return times. Calculator.net has a similar add-time feature but doesn't show the decimal hour alongside, which means a separate conversion step when you need to invoice for that time.

Sum a list of durations

The Sum durations tab totals any list of time spans. Enter each duration on its own line as H:MM — for example 1:30, 0:45, 2:15 — and the running total appears immediately as both H:MM and decimal hours. You can mix decimal inputs (1.5) with colon-format entries.

Timeanddate.com has no equivalent feature. The only way to total a list of durations there is to add them one pair at a time. This tab handles study sessions, workout segments, project task logs, or any series of time intervals in a single step without a spreadsheet.

Decimal hours for billing and payroll

Every result includes the decimal hours equivalent alongside the H:MM display. The conversion is simple — divide minutes by 60 — but easy to get wrong: 7 h 45 min is 7.75 h, not 7.45. Having the decimal ready means you can multiply directly by an hourly rate without an extra step.

For example, 6 h 20 min of billable work at $95 per hour: 6 + 20/60 = 6.333 h × $95 = $601.67. The calculator shows 6.33 so the arithmetic is immediate. This matters most when you bill by the quarter hour or need to paste a decimal into an invoice or payroll form.

How this compares to other time calculators

Rapidtables.com covers simple time subtraction and addition but has no sum-list feature and no overnight detection. Calculator.net has three separate time tools spread across different pages — subtraction, addition, and sum — requiring you to switch between them. Timeanddate.com's time zone calculator overlaps with duration math but isn't built for shift workers or invoicing.

This tool puts all three modes — between times, add/subtract, and sum — on a single page with consistent decimal output and overnight support. There's no login, no paywall, and no file upload. Everything runs in your browser.

Military time and 12/24-hour input

Time inputs accept both 12-hour (with AM/PM) and 24-hour (military) format depending on your browser locale. Type 14:30 for 2:30 PM or use the time picker — either works. The calculator always operates in 24-hour format internally and reports results unambiguously, so there's no confusion between 12:00 AM and 12:00 PM. Works on iPhone, Android, and desktop browsers equally well with no app to install.

Why time arithmetic isn't the same as decimal arithmetic

The most common mistake in manual time addition is treating hours and minutes as if they share the same base. They don't. Hours and minutes use base-60 (sexagesimal) notation, not base-10. When you add 1:45 and 0:30 as if they were ordinary numbers you get 1:75 — which isn't a valid time. The correct process is to carry at 60: 45 + 30 = 75 minutes, carry 1 hour, leaving 15 minutes, giving a total of 2:15. The same modulo-60 carry applies to seconds rolling into minutes.

This is also why 1 hour 30 minutes is not written as 1.30 in time notation — 1.30 in decimal is 1 hour 18 minutes (0.30 × 60 = 18 min), while 1:30 in H:MM is 1 hour 30 minutes. ISO 8601 uses a different, unambiguous notation: P1DT3H30M means a duration of 1 day, 3 hours, and 30 minutes; the leading P marks it as a period and T separates the date part from the time part. For software integrations that consume duration values, the ISO 8601 format avoids ambiguity completely.

Negative durations — time differences that cross midnight or where the end precedes the start — require an extra step. If end_minutes − start_minutes gives a negative result, add 1,440 (the total minutes in a day). A shift from 23:00 to 07:15 gives 435 − 1,380 = −945; adding 1,440 yields 495 minutes = 8 h 15 min. Always verify whether your tool handles this automatically, because a naive subtraction will silently return a wrong negative value.

Time tracking, payroll rounding, and FLSA compliance

Payroll systems almost universally store time in decimal hours, not H:MM, because payroll arithmetic requires multiplication by an hourly rate. 45 minutes becomes 0.75 h (45 ÷ 60), and a rate of $22/h × 0.75 = $16.50. Writing 0.45 instead of 0.75 — the classic base-60 confusion — understates pay by $6.60 per occurrence, which compounds significantly across a workforce.

US employers operating under the Fair Labor Standards Act (FLSA) must record all hours worked accurately, but the regulations permit a specific rounding rule: time can be rounded to the nearest five minutes, one-tenth of an hour, or quarter-hour, provided the rounding averages out in the employee's favor over time. The most common implementation rounds to the nearest 15-minute increment — 1 to 7 minutes rounds down to the previous quarter-hour, and 8 to 14 minutes rounds up to the next. For example, clocking in at 8:07 becomes 8:00; clocking in at 8:08 becomes 8:15. This rounding must be neutral or favorable to the employee over a pay period, not systematically used to shave time.

Overtime rules differ by jurisdiction. In the United States, the FLSA requires 1.5× the regular rate for all hours over 40 hours in a workweek (and some states like California require daily overtime beyond 8 hours). The UK has no statutory overtime multiplier — entitlement and rate depend entirely on the employment contract — but workers must receive at least the National Minimum Wage when averaged across all hours. Calculating weekly totals and spotting the overtime threshold is where a time duration calculator directly feeds into a payroll worksheet.

Duration estimation and the Planning Fallacy

Psychologists Daniel Kahneman and Amos Tversky identified the Planning Fallacy in 1977: people systematically underestimate how long tasks will take, even when they are fully aware that similar past tasks ran over schedule. The bias persists because estimators focus on the specific scenario in front of them — the best-case sequence of steps — rather than on the statistical distribution of how long similar tasks have actually taken in the past. Accurately summing durations after the fact is therefore not just an accounting exercise: comparing logged actuals against estimates is the feedback loop that calibrates future planning.

The standard corrective is reference class forecasting: instead of reasoning from the inside view ('this project has four phases and each phase should take two weeks'), look at the outside view — how long did the last ten comparable projects actually take? Project managers following the PMI PMBOK framework address this through schedule reserve. PMBOK recommends adding a 10–20% contingency buffer to the critical path duration, on top of individual activity reserves, to account for unforeseeable delays. Tracking actual durations with a time calculator is the foundation for calculating how accurate your reserves are.

At the micro level, the Pomodoro Technique uses fixed 25-minute work intervals followed by 5-minute breaks to make duration estimation concrete. After logging several Pomodoros you accumulate a dataset — how many 25-minute blocks does a 'small task' actually require versus how many you predicted? The Sum durations tab is a natural fit here: log each Pomodoro interval, total them, and compare against the estimate. Over time, the logged totals replace intuition with evidence.

Time zones, DST, and cross-timezone duration pitfalls

A flight departing London (UTC+0) at 10:00 and landing in New York (UTC−5) at 13:00 local time is not 3 hours long — it is 8 hours long. The correct calculation always converts both endpoints to the same reference: 10:00 UTC departure, 13:00 EST = 18:00 UTC arrival, 18:00 − 10:00 = 8 hours. Whenever a duration spans different time zones, both times must be converted to UTC first before subtracting. Failing to do this is the most common error in scheduling international meetings and flight itineraries.

Daylight Saving Time (DST) introduces a further wrinkle: on the day clocks spring forward, the day is only 23 hours long, and on the day clocks fall back it is 25 hours long. A shift spanning the spring-forward transition that runs from 23:00 to 07:00 is actually only 7 hours, not 8 — one hour vanished at 2:00 AM. The reverse happens in autumn: a night shift crossing the fall-back gains an hour of actual time that won't appear in a naive H:MM subtraction. Systems that store timestamps in UTC sidestep this entirely, because UTC has no DST transitions; the conversions to local time happen only for display.

For this tool, which operates on clock-face times within a single calendar day, the practical advice is to record times in UTC when accuracy across DST boundaries matters, and to manually adjust by the DST offset (±1 hour) when a shift straddles a clock-change moment. Duration calculators that work purely with H:MM inputs cannot know the date, so they cannot resolve DST automatically — that requires a full datetime value (date + time + timezone), the domain of dedicated scheduling libraries like Temporal in JavaScript or the datetime module in Python.