Time Duration Calculator

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 0–24 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: P2H30M 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). Marathon times: 2:01:39 is the world record (Kelvin Kiptum, 2023). Sprint times: 100m world record = 9.58 seconds. Formula 1 lap times: typically 70–90 seconds per lap, measured to 0.001 seconds. Swimming: 50m freestyle world record = 20.91 seconds. 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 supports both: just enter hours 0–23 and leave the AM/PM buttons to indicate the 12-hour format if preferred.

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.