Time & Date · Updated

Time Duration Calculator

Calculate the exact duration between two times, add and subtract multiple time values, or convert any duration to hours, minutes, seconds, and decimal formats.

Last updated

Start & End Time
Add & Subtract Durations
HH:MM:SS Precision
Decimal Conversion
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Time Duration Calculator
Two modes: Between times & Add/Subtract
: :
hoursminsec
: :
hoursminsec
If end is before start, the calculator assumes end is on the next day.

Enter time values above to calculate the duration.

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How to Calculate Time Duration

Subtract the start time from the end time, and add 24 hours first if the end is earlier. 9:15:30 AM to 5:40:45 PM is 8 hours 25 minutes 15 seconds, or 8.4208 decimal hours. Enter two times above, or add and subtract a list of durations, and the calculator shows the result as HH:MM:SS, decimal hours, total minutes and total seconds.

Time duration calculation is the process of finding the total elapsed time between a start time and an end time. It is used in work scheduling, project tracking, billing, sports timing, cooking, and daily planning. The basic method is to subtract the start time from the end time, but this becomes more complex when the duration crosses midnight or involves multiple days.

The most common use case is calculating work hours. If you start at 9:00 AM and finish at 5:30 PM, the duration is 8 hours 30 minutes. If you take a 45-minute lunch break, the net working time is 7 hours 45 minutes. This calculator handles all these scenarios including overnight durations that cross midnight.

Work Hours
Calculate billable hours, overtime, and shift lengths. Enter clock-in and clock-out times for exact results including breaks.
Overnight Shifts
When end time is earlier than start time, the calculator automatically detects an overnight duration crossing midnight and adds 24 hours.
Project Tracking
Track time spent on tasks and projects. Add multiple durations together to get total hours for invoicing or reporting.
Time Formats
Results shown in hours and minutes, decimal hours (useful for payroll), total minutes, and total seconds. 7h 30m = 7.5 decimal hours.

Time Units Conversion Table

Decimal hours = hours + minutes ÷ 60 + seconds ÷ 3,600.

DurationMinutesSecondsDecimal hours
15 minutes159000.25
30 minutes301,8000.50
45 minutes452,7000.75
1 hour603,6001.00
1 hour 30 minutes905,4001.50
2 hours 30 minutes1509,0002.50
8 hours48028,8008.00
24 hours1,44086,40024.00
1 week10,080604,800168.00

Three Worked Examples

A shift that crosses midnight, with seconds

Start 10:45:20 PM (22:45:20), end 7:10:05 AM. The end is earlier, so add 24 hours: 31:10:05. Now subtract, borrowing where needed: 5 seconds minus 20 needs a borrowed minute (65 minus 20 = 45 seconds), 9 minutes minus 45 needs a borrowed hour (69 minus 45 = 24 minutes), and 30 minus 22 = 8 hours. Duration: 8:24:45.

Adding lap times

Three laps of 12:48, 13:05 and 12:57 (minutes and seconds). Seconds: 48 + 5 + 57 = 110, which is 1 minute 50 seconds. Minutes: 12 + 13 + 12 = 37, plus the carried minute is 38. Total: 38:50.

Subtracting one duration from another

4 h 35 m minus 1 h 50 m. You cannot take 50 minutes from 35, so borrow an hour: 3 h 95 m minus 1 h 50 m = 2 h 45 m, which is 2.75 decimal hours.

Mistakes That Give Wrong Durations

  • Reading 1:30 as 1.3. One hour thirty minutes is 1.5 hours. Multiplying 1.3 by a pay rate underpays by 12 minutes.
  • Mixing up 12 AM and 12 PM. 12:00 AM is midnight (00:00) and 12:00 PM is noon. A shift from 12 PM to 8 PM is 8 hours; from 12 AM to 8 PM it is 20.
  • Forgetting the clock change. The calculator works with clock times, not dates. On the night US clocks fall back (Sunday 1 November 2026) a 10 PM to 6 AM shift really lasts 9 hours, and on the night they spring forward (Sunday 14 March 2027) it lasts 7. Add or take off the hour yourself for those two nights.
  • Adding minutes past 59 without carrying. 2 h 45 m + 1 h 30 m is 3 h 75 m, which you must write as 4 h 15 m.

For timesheets with breaks and pay, the Hours Calculator and the Work Hours Calculator are quicker. For spans measured in days, use Days Between Dates.

Method and sources. Both times are converted to seconds after midnight; duration = end minus start, plus 86,400 seconds when the end is earlier than the start. Results are then split back into hours, minutes and seconds. Unit definitions follow the SI second (NIST). Duration notation follows ISO 8601. Daylight saving dates follow the US rule set by the Energy Policy Act of 2005: second Sunday in March to first Sunday in November.
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Time Duration Questions

Convert both times to seconds from midnight (or any reference point), then subtract. Example: start 9:00:00 AM = 9 × 3600 = 32,400 seconds. End 5:30:00 PM = 17.5 × 3600 = 63,000 seconds. Duration = 63,000 − 32,400 = 30,600 seconds = 8 hours 30 minutes. If the end time is earlier than the start (e.g., a night shift from 10 PM to 6 AM), the calculator automatically adds 86,400 seconds (one day) to the end time before subtracting.

Time (or a time of day) is a specific point on the clock: 3:45 PM, 09:30:00. Duration is a span of time without reference to a clock position: 2 hours 15 minutes, 45 seconds. You calculate duration by subtracting one time from another. Duration can exceed 24 hours (e.g., a project took 36 hours 20 minutes), but a time of day is always within 0 to 24 hours. This calculator shows duration in HH:MM:SS format, decimal hours, total minutes, and total seconds.

Use the Add / Subtract tab. Enter each duration (hours, minutes, seconds) and toggle the +/− sign to add or subtract it. The calculator converts everything to seconds internally, sums them, then converts back. Example: 2h 30m + 1h 45m + 0h 20m = (9000 + 6300 + 1200) seconds = 16,500 seconds = 4h 35m. This is useful for totaling video lengths, lap times, project time logs, or any collection of time spans.

Divide minutes by 60 and seconds by 3600, then add to the whole hours. Formula: decimal = hours + (minutes / 60) + (seconds / 3600). Examples: 2h 30m 0s = 2 + 30/60 = 2.5000 hours. 1h 45m 30s = 1 + 45/60 + 30/3600 = 1.7583 hours. 0h 20m 15s = 0 + 20/60 + 15/3600 = 0.3375 hours. Decimal hours are used in payroll, billing, and scientific calculations. Multiply by your hourly rate to calculate pay.

1 minute = 60 seconds. 1 hour = 3,600 seconds. 1 day = 86,400 seconds. 1 week = 604,800 seconds. 1 month (30 days) = 2,592,000 seconds. 1 year = 31,536,000 seconds (31,622,400 in a leap year). These are exact values for calendar units. For average month: 30.4375 days × 86,400 = 2,629,800 seconds. Unix timestamps count seconds since January 1, 1970 00:00:00 UTC, useful in computing for measuring durations precisely.

In everyday use, "time span" and "time interval" are interchangeable. In computing and formal mathematics, an interval often has defined start and end points (e.g., [9:00, 17:00]) while a duration or span is just the magnitude (8 hours). ISO 8601 defines duration format as P[n]Y[n]M[n]DT[n]H[n]M[n]S: PT2H30M means a duration of 2 hours 30 minutes. The "P" stands for "period" and "T" separates date from time components. PT30M = 30 minutes. P1DT2H = 1 day 2 hours.

If your shift or task runs past midnight (e.g., 10:00 PM to 6:00 AM), the end time appears earlier than the start time on a 12-hour or 24-hour clock. This calculator detects this automatically: if end time in seconds ≤ start time in seconds, it adds 86,400 seconds (one full day) to the end time. So 10:00 PM to 6:00 AM = 22:00 to 06:00 = 6×3600 + 86400 − 22×3600 = 21600 + 86400 − 79200 = 28,800 seconds = exactly 8 hours.

Sports timing uses HH:MM:SS.mmm format (with milliseconds). A marathon finish is written in hours, minutes and seconds (2:05:30), a 100 m sprint in seconds to the hundredth (9.85), and a Formula 1 lap to the thousandth of a second (1:21.456). In multi-stage events like the Tour de France, accumulated durations across stages are summed to find the overall leader: exactly what the Add/Subtract tab in this calculator does.

Military time (24-hour clock) eliminates AM/PM confusion. To convert: AM hours stay the same (8:30 AM = 08:30). Noon = 12:00. PM hours: add 12 to the 12-hour PM time (except 12 PM noon, which stays 12:00). 1:00 PM = 13:00. 5:45 PM = 17:45. 11:59 PM = 23:59. Midnight = 00:00. To convert back: subtract 12 from any hour > 12 and add PM. 15:30 = 3:30 PM. This calculator accepts both: enter 1 to 12 and pick AM or PM, or type 13 to 23 (0 for midnight) and the AM/PM buttons are ignored.

Video uses SMPTE timecode: HH:MM:SS:FF where FF is frames. At 24 fps (cinema), each second has 24 frames. At 30 fps (broadcast TV), 30 frames. At 60 fps (sports, high-speed), 60 frames. One frame at 24 fps = 1/24 second ≈ 41.67ms. A feature film at 1h 52m 0s = 6,720 seconds × 24 fps = 161,280 frames. "Drop frame" timecode adjusts for the fact that color TV actually runs at 29.97 fps, not exactly 30. This calculator works with HH:MM:SS but ignores sub-second frames, for frame-level precision, use a dedicated NLE or timecode calculator.

Take the decimal part and multiply by 60 for minutes, then multiply any leftover decimal by 60 again for seconds. 1.7583 hours is 1 hour 45 minutes 30 seconds: 0.7583 × 60 = 45.5 minutes, and 0.5 × 60 = 30 seconds. For quick checks, 0.25 is 15 minutes, 0.5 is 30 and 0.75 is 45.

One hour longer or shorter than the clock times suggest. On Sunday 1 November 2026, when US clocks go back from 2:00 AM to 1:00 AM, a 10 PM to 6 AM shift lasts 9 hours of real time. On Sunday 14 March 2027, when clocks jump from 2:00 AM to 3:00 AM, the same shift lasts 7 hours. Under federal wage rules you are paid for the time actually worked, so the extra hour in November counts.
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