The Time Duration Calculator finds the exact elapsed time between any two clock times — in hours and minutes, total minutes, total seconds, and decimal hours. Enter a start time and an end time and it instantly shows how long the interval lasts, with every calculation step shown so you can verify the result yourself. It handles overnight spans that cross midnight, which is where most manual time math goes wrong.
People use duration math constantly: timing a work shift, measuring a flight, tracking a recipe, logging study sessions, or billing clients by the hour. Doing it by hand means borrowing 60 minutes across the hour boundary and remembering whether 2:00 PM comes before or after midnight — small slips that produce answers off by a full hour or a whole day. This calculator removes that risk and documents its work.
Elapsed time (or duration) is the amount of time between two instants. Clock time is measured on a repeating 24-hour cycle, which makes duration arithmetic different from ordinary subtraction: when the end time is numerically smaller than the start time, the interval has wrapped past midnight and you must add a full day (1,440 minutes) before subtracting.
The reliable method is to convert both times to minutes after midnight. 09:00 becomes 540 minutes, 17:30 becomes 1,050 minutes, and the difference — 510 minutes — divides cleanly into 8 hours and 30 minutes. Working in a single unit avoids the awkward borrowing (for example, 5:10 minus 3:45) that trips people up.
Decimal hours express the same duration as a fraction of an hour: 8 hours 30 minutes is 8.50 hours, 8 hours 15 minutes is 8.25 hours. Payroll systems, billing software, and timesheets almost always want decimal hours, so the calculator provides them alongside the familiar hours-and-minutes form.
Duration (minutes) = Endmin − Startmin (+ 1,440 if the result is negative)
Hours = ⌊Duration ÷ 60⌋ · Minutes = Duration mod 60 · Decimal hours = Duration ÷ 60
Each clock time converts to minutes after midnight with minutes = hours × 60 + minutes. If the end time falls on the next calendar day, add 1,440 minutes (24 × 60) to the difference. The total then splits into whole hours and a remainder of minutes, and dividing by 60 once more gives decimal hours.
Example 1 — a standard workday. Start 09:00, end 17:30. Convert: 9 × 60 = 540 minutes; 17 × 60 + 30 = 1,050 minutes. Subtract: 1,050 − 540 = 510 minutes. Split: 510 ÷ 60 = 8 remainder 30, so the duration is 8 hours 30 minutes, or 8.50 decimal hours, or 30,600 seconds.
Example 2 — crossing midnight. Start 22:00, end 06:00, overnight checked. Convert: 22 × 60 = 1,320 minutes; 6 × 60 = 360 minutes. Subtract: 360 − 1,320 = −960 minutes — negative, so add 1,440: 480 minutes. Split: 480 ÷ 60 = 8 remainder 0, so the duration is 8 hours exactly.
Example 3 — a short interval. Start 14:45, end 15:20. Convert: 885 and 920 minutes. Difference: 35 minutes, which is 0 hours 35 minutes, or 0.58 decimal hours (35 ÷ 60 = 0.5833…).
Maria clocks in at 08:47 and clocks out at 16:12. Her timesheet needs decimal hours. Start: 8 × 60 + 47 = 527 minutes. End: 16 × 60 + 12 = 972 minutes. Duration: 972 − 527 = 445 minutes. That is 7 hours 25 minutes, and 445 ÷ 60 = 7.42 decimal hours — the figure she enters on her timesheet. Without the calculator, the borrow across the hour boundary (12 − 47) is exactly where errors creep in.
A flight departs at 21:35 and lands at 07:05 the next morning. Start: 1,295 minutes; end: 425 minutes; raw difference −870, plus 1,440 = 570 minutes = 9 hours 30 minutes. Knowing the true block time helps travelers judge whether a 45-minute connection after landing is realistic.
Time duration math is simple in principle — convert to minutes, subtract, split back into hours — but the base-60 borrowing and midnight wrap make it error-prone by hand. This calculator handles the conversion, the overnight adjustment, and the decimal-hours output in one step, with full working shown. For payroll, add your rounding rule after computing the exact duration; for billing, apply minimum increments last. When in doubt between AM and PM, switch to 24-hour time and the ambiguity disappears.
The Time Card Calculator totals a full week of clock-in/clock-out entries for payroll. The Hours Calculator adds or subtracts hours from a starting time. The Date Difference Calculator measures elapsed time across calendar days instead of clock times.
The Time Duration Calculator at Sigma Calculator computes elapsed time between two clock times. Method: convert each time to minutes after midnight, subtract (adding 1,440 minutes when the interval crosses midnight), then express the result as hours and minutes, total minutes, total seconds, and decimal hours, with step-by-step working shown.
The 24-hour clock (military time) writes times from 00:00 to 23:59, eliminating AM/PM ambiguity entirely. 2:30 PM becomes 14:30; midnight is 00:00 and noon is 12:00. Hospitals, airlines, railways, and the military use it precisely because duration math becomes trivial: 14:30 to 22:15 is 22×60+15 − (14×60+30) = 465 minutes, or 7 hours 45 minutes, with no AM/PM conversion step to get wrong.
Time arithmetic borrows in base 60, not base 10. Subtracting 3:45 from 5:10 by hand: the minutes column needs 10 − 45, so borrow one hour (60 minutes): 70 − 45 = 25 minutes, hours 4 − 3 = 1, giving 1 hour 25 minutes. The classic error is borrowing 100 instead of 60, yielding 65 minutes — an answer that looks plausible but is wrong by 40 minutes. Converting everything to minutes-first, as this calculator does, sidesteps borrowing completely.
Time zones add another layer: a 9-hour flight departing 10:00 local and landing 19:00 local might actually be 9 hours or 11 hours depending on zone changes. Always convert both endpoints to a common reference (UTC) before subtracting. Daylight saving transitions create 23-hour and 25-hour days; a “24-hour” shift spanning a spring-forward Sunday is really 23 hours of elapsed time. For payroll spanning such transitions, note the actual elapsed minutes rather than the nominal clock difference.
Decimal time (used in French Revolutionary calendars and some industrial timekeeping) divides the day into 10 hours of 100 minutes, but it never caught on — the world kept base-60 from Babylonian astronomy. Modern decimal hours (7.5 h) are the practical compromise: base-60 for human clocks, base-10 for computation and billing.
Beyond payroll, duration math underpins project estimation (summing task durations to find critical paths), fitness training (pace = duration ÷ distance), cooking (resting meat, proofing dough), and medication timing (doses every 6 hours means 00:00, 06:00, 12:00, 18:00 — drift by 30 minutes per dose compounds across a day). In each case the failure mode is the same: small arithmetic slips in base-60 that a calculator prevents.
Payroll systems live on decimal hours. A shift of 7 hours 45 minutes becomes 7.75; 8 hours 6 minutes becomes 8.10. The conversion rule — minutes ÷ 60, added to whole hours — is simple, but applied across hundreds of timesheet lines, manual conversion is a major error source. Most payroll disputes trace to exactly this: an employee writes 8.45 meaning “8 hours 45 minutes” while the system reads it as 8.45 decimal hours (8 hours 27 minutes), an 18-minute underpayment per shift.
Rounding rules vary by employer and jurisdiction: many round to the nearest quarter hour (7-minute rule in US federal guidance — 1–7 minutes round down, 8–14 round up to the quarter). Some use tenth-of-hour (6-minute) increments. Whatever the policy, the defensible workflow is: compute exact duration first (this calculator), then apply the rounding rule once, at the end. Rounding each clock-in/out before subtracting compounds errors.
Freelancers and consultants bill in decimal hours too, often with minimum increments (15 or 30 minutes). A 22-minute call billed at a 30-minute minimum is 0.50 hours, not 0.37. Tracking exact durations with a calculator and then applying minimums keeps invoices consistent and defensible when clients question them.
Convert both times to minutes after midnight, subtract the start from the end, and split the result into hours and minutes. If the end time is earlier than the start time, add 1,440 minutes (24 hours) first — the interval crossed midnight. The calculator above does all of this automatically and shows each step.
8 hours exactly. In minutes: 17:00 is 1,020 minutes after midnight and 09:00 is 540 minutes, so 1,020 − 540 = 480 minutes = 8 hours 0 minutes, or 8.00 decimal hours.
When the end time is on the next day, add 24 hours to the raw difference. For example, 10:00 PM to 6:00 AM: 360 − 1,320 = −960 minutes; adding 1,440 gives 480 minutes, which is 8 hours. Tick the overnight option in the calculator to apply this automatically.
Divide the minutes by 60 and add the whole hours. 7 hours 45 minutes = 7 + 45 ÷ 60 = 7.75 hours. Common values: 15 minutes = 0.25, 30 minutes = 0.50, 45 minutes = 0.75. Payroll and billing systems almost always use decimal hours.
Almost always an AM/PM mix-up or a missed borrow across the hour boundary. Double-check that 12:00 PM means noon and 12:00 AM means midnight, and when subtracting minutes (for example, 12 − 47) remember to borrow 60 minutes from the hours column, not 100.
510 minutes. Multiply decimal hours by 60: 8.5 × 60 = 510. Going the other direction, 510 ÷ 60 = 8.5 hours, which is 8 hours 30 minutes.
It measures a single clock-time interval up to just under 24 hours. For spans across multiple calendar days, use the Date Difference Calculator, which counts whole days between two dates.
Time is a point on the clock (3:30 PM); duration is the length of an interval between two points (2 hours 15 minutes). Duration is always a quantity of time, never a clock reading — that is why it is reported in hours and minutes rather than as a time of day.
Cite this page as: Time Duration Calculator — Sigma Calculator. https://sigmacalculator.net/time-date-calculators/time-duration-calculator/
Last updated: October 11, 2026