Time Calculator

A time calculator is a free, browser-based tool that adds or subtracts durations in hours, minutes, and seconds, and measures the elapsed time between two clock times. It converts each entry to total seconds, does the arithmetic, and returns the answer in h:m:s, digital HH:MM:SS, total seconds, total minutes, and decimal hours for timesheets. Updated 2026-08-11.

How the Time Calculator Works

This time calculator lets you add or subtract time durations expressed in hours, minutes, and seconds. It converts everything to total seconds internally, performs the arithmetic, then converts back to a readable hours:minutes:seconds format. The calculator handles overflow automatically — for example, 75 minutes becomes 1 hour and 15 minutes.

You can use this for calculating total work hours, adding up exercise durations, figuring out cooking times, computing travel durations, or any situation where you need to add or subtract time values. Enter the first time, choose add or subtract, enter the second time, and get your result instantly.

Example Calculations

Duration Between Two Clock Times (Including Overnight Shifts)

Set the Operation dropdown to Duration between two clock times and the two entries stop being durations and become points on a 24-hour clock. Enter 22 h 30 m as Time 1 and 6 h 15 m as Time 2 and the answer is 7 hours 45 minutes, not a negative number — an end time earlier than the start is read as the next day, which is what an overnight shift actually is. Enter clock times in 24-hour form: 9:15 AM is 9 h 15 m, and 5:30 PM is 17 h 30 m. The result also reports decimal hours (7.75), which is the format US payroll systems expect; the US Department of Labor recordkeeping rules (Fact Sheet 21) require employers to keep the hours worked each day and each workweek, so this is the number that belongs on the timesheet.

Common Uses for Time Calculation

Time calculators are used daily by employees tracking work hours, runners adding lap times, cooks combining recipe preparation and cooking durations, project managers estimating task completion, students calculating study time, and travelers adding flight durations with layovers. Any scenario where you need to combine or compare time durations benefits from a simple time calculator.

Entering PM and Military Time in the Time Calculator

The Time 1 and Time 2 boxes use the 24-hour clock, so an afternoon time has to be entered as its 24-hour value or the answer comes out wrong. The rule is simple: for any PM time except noon, add 12 to the hour. 1 PM is 13, 5 PM is 17, 9:15 PM is 21 h 15 m, and 11:45 PM is 23 h 45 m. Going the other way, 12 AM (midnight) is 0, and 12 PM (noon) stays 12 — those two are the pair people reverse most often. Military and 24-hour notation drop the colon, so "1730" means 17 h 30 m, and "0045" means 0 h 45 m. The United States civil day officially starts at 00:00:00 and runs to 23:59:59, as defined by the NIST Time and Frequency Division. If your shift crosses midnight, enter both times as 24-hour values and switch the Operation dropdown to "Duration between two clock times" — the calculator rolls over to the next day instead of returning a negative. Updated 2026-08-18.

Converting Time to Decimal Hours for Payroll

Payroll systems do not accept 7 hours 45 minutes — they want 7.75. The conversion is one division: take the minutes, divide by 60, and add the result to the hours. So 7h 45m becomes 7 + (45 ÷ 60) = 7.75, 6h 20m becomes 6 + (20 ÷ 60) = 6.33, and 8h 10m becomes 8.17. The mistake that costs real money is writing 7.45 for 7h 45m — that is 7 hours 27 minutes, and repeated across a fortnightly timesheet it quietly removes close to an hour of paid work.

The quick reference for common minute values: 5m = 0.08, 10m = 0.17, 15m = 0.25, 20m = 0.33, 30m = 0.50, 40m = 0.67, 45m = 0.75, 50m = 0.83. Add the duration in this calculator first, then convert the total once at the end rather than converting each shift — converting early and rounding each line is where cumulative error creeps in.

On rounding: US employers may record time in quarter-hour increments, but under 29 CFR § 785.48 the practice is only lawful if it averages out neutrally over time — rounding that consistently favours the employer is not permitted. The common compliant pattern is the 7-minute rule: minutes 1-7 past a quarter round down, minutes 8-14 round up. Keep the exact clock times as well as the rounded figure, since the exact record is what settles a dispute. Updated 2026-08-26.

Hours, Minutes and Seconds Calculator

Used as an hours, minutes and seconds calculator, this tool takes three separate boxes per entry instead of one clock field, so you never have to normalise your numbers first. Type 2 h 90 m 200 s and it returns 3 h 33 m 20 s — the overflow is carried automatically because every entry is converted to total seconds before the arithmetic runs. That total-seconds figure is reported back to you as its own line, which is what you want when a query is really "calculate seconds": 1 h 45 m 30 s is 6,330 seconds. The second is the SI base unit of time and is defined by the caesium-133 hyperfine transition frequency of 9,192,631,770 Hz, per the BIPM SI definition of the second; every conversion on this page is an exact integer multiple of it, so nothing here is a rounded approximation. Minutes and seconds on their own work the same way — leave the hours boxes at 0 and the calculator behaves as a minutes-and-seconds calculator for lap times, podcast segments or race splits. Updated 2026-09-09.

Why Your Timesheet Total Differs From This Calculation

People often reach this calculator because a payroll total did not match the hours they worked, and rounding is usually the reason rather than an error. Many US employers record clock-in and clock-out to the nearest quarter hour instead of the exact minute. Under the federal rule that practice is permitted only where it is neutral over time — rounding that consistently favours the employer, so that workers are never fully paid for the time they actually worked, is not allowed. The practical effect is that a shift from 8:58 to 17:04 may be paid as 9:00 to 17:00, and a handful of those across a fortnight is enough to explain a missing quarter of an hour on the payslip. The calculator above gives you the exact figure to the minute, and the decimal-hours conversion gives you the number payroll systems actually work in, so you can put a precise total next to the rounded one before raising it. Keep your own record of real clock times; a dispute is settled on what was worked, not on what the terminal rounded it to. Source: U.S. Department of Labor — Wage and Hour Division, FLSA. Updated 2026-09-18.

Time Conversion Reference

For quick reference: 1 hour = 60 minutes = 3,600 seconds. 1 day = 24 hours = 1,440 minutes = 86,400 seconds. 1 week = 168 hours. When a result runs past 24 hours the calculator keeps showing the running total in hours (e.g., 26 hours 15 minutes), which is what timesheets need, and adds a separate Days · Hours · Minutes line so a long total like 390 hours is also readable as 16 d 6 h 0 m without a second calculation.