Hours and Minutes Calculator

DateMath turns every amount into seconds, adds or subtracts the seconds, and only then writes the total back as hours, minutes and seconds, so 45 minutes plus 30 minutes carries to 1:15:00, never 0:75. To multiply or divide, DateMath scales the seconds by the number and rounds the result to the nearest second. Decimal hours are the seconds divided by 3,600, rounded to two places at the end.

• Units of time. DateMath uses the fixed units the International System of Units (SI) accepts for use with the second: a minute is 60 seconds, an hour 60 minutes (3,600 seconds) and a day 24 hours (86,400 seconds), so amounts of time carry at 60, not at 100. Source: SI Brochure (BIPM).

DateMath's date math is tested against more than 100 cases worked out by hand. Every worked example and table on the site is computed with the same code the calculators run, so a page and its calculator can't disagree.

The hours and minutes calculator does arithmetic on amounts of time, not on clock times. Add the lengths of songs, laps, calls or work sessions, take some off, or split a total into equal parts, and the answer comes back in hours, minutes and seconds with every carry already done. It is an hours adding calculator and an hours addition calculator for timesheets, and a minutes and seconds calculator for anything shorter.

What you enter

• Add and subtract: up to 10 rows, each with hours, minutes and seconds and a + or − sign. Any field can be left empty, and minutes or seconds over 59 carry over, so 90 minutes or 150 seconds go in as they are.
• Multiply or divide: one amount of time and the number to multiply or divide it by. The number may have decimals, such as 1.5 or 26.2.

What you get

The headline is the total as h:mm:ss, such as 5:12:05 for the calculator's sample. Below it you get the same total in words (5 hours, 12 minutes, 5 seconds), as decimal hours (5.20), as total minutes and total seconds, and in days, hours, minutes and seconds once it reaches a day. A shared link carries every row, so a colleague sees the same sum.

For a time of day plus an amount, such as 8 hours after 10:30 PM, use the time calculator; for the hours between two clock times, the hours calculator; and for a week of time in and time out, the time card calculator.

Write each amount as h:mm:ss, one under the other, and add from the right. Seconds and minutes carry at 60, not at 10: every 60 seconds make a minute and every 60 minutes an hour. Example: 1:25:40, 2:48:35 and 0:57:50.

1. Seconds: 40 + 35 + 50 = 125, which is 2 minutes and 5 seconds. Write 5, carry 2.
2. Minutes: 25 + 48 + 57 + 2 carried = 132, which is 2 hours and 12 minutes. Write 12, carry 2.
3. Hours: 1 + 2 + 0 + 2 carried = 5.

Result: 5:12:05, or 5 hours, 12 minutes, 5 seconds, the same as the calculator gives. DateMath does the same sum in seconds: it turns every row into seconds, adds them, and writes the total back as hours, minutes and seconds, so no carry is ever lost.

Subtract from the right as well. When a unit is too small, borrow 1 from the unit to its left, which gives 60 of the smaller one. Example: 5:12:05 − 2:48:35.

1. Seconds: 5 is less than 35, so borrow 1 minute: 5 + 60 = 65, and 65 − 35 = 30.
2. Minutes: 12 − 1 lent = 11. 11 is less than 48, so borrow 1 hour: 11 + 60 = 71, and 71 − 48 = 23.
3. Hours: 5 − 1 lent − 2 = 2.

Result: 2:23:30. In the calculator, set the second row to "− Subtract". When you take away more than you add, the total is negative and starts with a minus sign, which is handy for checking how far a week is short of a target: 37:30 worked against 40:00 planned is −2:30:00.

To divide an amount of time, turn it into one unit, divide, and turn the result back. 37 hours 30 minutes is 2,250 minutes, and 2,250 ÷ 5 = 450 minutes, which is 7 hours, 30 minutes. Multiplying works the same way. The calculator does it in seconds and rounds the answer to the nearest second.

Some divisions don't come out even: an hour divided by 7 is 514.286 seconds, so the calculator shows 0:08:34 and says it rounded. Dividing a race time by its distance gives a pace: a marathon of 26.2 miles in 4:30:00 is 10:18 per mile.

Short durations are usually written as m:ss, and adding them is a minutes and seconds adder job. Type 0 hours (or leave Hours empty) and enter the minutes and seconds of each one. A playlist of 3:42, 4:15, 2:58, 5:31, 3:09 and 4:47 runs 24:22, 24 minutes, 22 seconds.

Lap times work the same way: 1:32, 1:29, 1:35 and 1:31 add up to 6:07, an average of 1:32 per lap, the total divided by 4 in "Multiply or divide". Times with tenths or hundredths of a second need rounding to whole seconds first; the fields take whole numbers.

A calculator or spreadsheet that reads 1:45 as 1.45 adds it like money, carrying at 100, and gets the wrong total. Hours and minutes carry at 60, so the hundredths column never applies. These sums show the gap:

If a timesheet already has decimal hours, such as 7.75, add those as decimals; just don't mix the two forms in one sum. The hours to decimal calculator converts between them, with a chart for every minute.

The result shows each total five ways, because each place wants a different one: h:mm:ss for a log or a video editor, words for a message, decimal hours for pay and invoices, total minutes for a phone plan, and total seconds for code or a stopwatch.

A week of daily totals, 7:50, 8:15, 7:40, 8:05 and 6:30, adds up to 38:20, which is 38.33 decimal hours. When you have the times in and out instead of the daily totals, the time card calculator works each day out and adds the week, with breaks and gross pay; to find when a shift ends, use the shift calculator.

• Enter durations as h:mm:ss, such as 1:25:40. Excel reads 25:40 as 25 hours 40 minutes, so type 0:25:40 for 25 minutes 40 seconds.
• Add them with =SUM(A1:A10) and format the result as [h]:mm:ss. The brackets let the hours run past 24; without them, 26:15:00 shows as 2:15:00.
• Subtract with =A1-A2. Excel shows a negative time as ###### in its default 1900 date system, so subtract the smaller amount from the larger one.
• Divide or multiply with =A1/5 or =A1*1.5, and convert to decimal hours with =A1*24, formatted as a number.

• Total hours. The hours of a project, a course or a volunteer log, from many sessions.
• Media and music. The running time of a playlist, an album, a set of clips or a podcast season.
• Sport. Split times, lap totals, average laps and a race pace per mile or kilometer.
• Sharing time out. A shift or a budget of hours divided between people or days.

For dates instead of hours, the date duration calculator measures the time between two dates and times.