Time Calculator

How adding time works when units carry at 60

Time is counted in base 60, not base 10, and that single fact explains almost every mistake people make with it. Sixty seconds make a minute, sixty minutes make an hour, twenty-four hours make a day. When you add spans, you add each unit on its own and then carry anything over the limit into the next unit.

So 45 minutes plus 30 minutes is not 75 minutes in any useful form, it is 1 hour 15 minutes. The calculator on this page does that carrying for you across hours, minutes and seconds, and it also shows the total in decimal hours, which is the form most payroll and billing systems want.

• Seconds: add them, carry 60 into minutes.
• Minutes: add them plus any carry, carry 60 into hours.
• Hours: add them plus any carry, and keep going past 24 if the total is longer than a day.

One thing to keep separate: a duration and a clock time are different animals. A duration of 26 hours is a normal total for a project log. A clock reading of 26:00 does not exist, because the clock wraps back to 2:00. The section on totals past 24 hours covers that split in more detail.

Worked example: four spans that add up to 5 hours 30 minutes

Say a freelancer logs four sessions in a day: 1:45:00 on one client, 0:50:30 on a second, 2:15:00 on a third, and 0:40:00 on admin. Add the seconds first, then the minutes, then the hours.

• Seconds: 0 + 30 + 0 + 0 = 30 seconds, no carry.
• Minutes: 45 + 50 + 15 + 40 = 150 minutes, which is 2 hours 30 minutes.
• Hours: 1 + 0 + 2 + 0 = 3 hours, plus the 2 carried hours = 5 hours.
• Total: 5:30:30, or 5.5083 decimal hours.

In minutes that is 330.5, and in seconds 19,830. At a billing rate of $40 an hour the session total is $220.33, which is the kind of number an invoice needs. If you bill by the quarter hour instead, 5:30:30 rounds to 5.5 hours and the invoice line becomes $220.00.

This is the same arithmetic a timesheet does, but the output here is a duration, not a paycheck. If you want the weekly pay version, with the first 40 hours at your regular rate and the rest at time and a half, the time card calculator handles that split. Use this page when the question is how long something took, and that page when the question is what the week pays.

Worked example: a shift minus an unpaid break

Subtraction is just addition with a negative span, and the most common case is a lunch break. A shift runs from 9:10 to 17:40, with 45 minutes unpaid for lunch.

• Clock time on the job: 17:40 minus 9:10 = 8 hours 30 minutes, or 510 minutes.
• Minus the break: 510 minus 45 = 465 minutes.
• In hours and minutes: 7:45.
• In decimal hours: 465 divided by 60 = 7.75.

At $18 an hour that day is worth $139.50 before tax. Note how the decimal form and the clock form disagree if you read them carelessly: 7:45 is 7.75 hours, not 7.45 hours. The gap between 7.45 and 7.75 is 18 minutes, which over a year of shifts is real money.

The calculator takes the break as a negative row, so enter the break time and set that row to subtract, or enter the shift total and subtract the break in a second row. Both give the same 7:45.

Decimal hours and the conversion table payroll uses

Payroll software, invoicing tools and project trackers store time as a decimal fraction of an hour, because multiplying a decimal by an hourly rate is one step. The conversion is a straight division by 60, and the table below covers the fractions that come up in practice.

Read the 45 row twice. An hour and 45 minutes is 1.75 hours. An hour and 25 minutes is 1.4167 hours. People type 1.25 for 1 hour 25 minutes all the time, and that turns a 85 minute session into a 75 minute one.

The widget converts in both directions: put a decimal such as 7.75 into the decimal box and it returns 7 hours 45 minutes, which is the check to run before you hand a timesheet to anyone.

Rounding to the nearest quarter hour and the 7 minute rule

Many employers record start and stop times to the nearest quarter hour, and federal rules allow it under 29 CFR 785.48(b) as long as the practice averages out over time and does not leave workers unpaid for time they worked. The Department of Labor explains the practical version in Fact Sheet 53: minutes 1 through 7 after a quarter hour round back, and minutes 8 through 14 round forward.

Two cautions. First, rounding only one direction is the violation: if every punch is rounded down, the employer is taking time. Second, the rounding applies to the punch, not to the daily total. A day recorded as 8:52 to 17:08 rounds to 8:45 and 17:15, which is 8.5 hours, not the 8 hours 16 minutes on the clock.

If you are checking a stub and the hours look short, convert both the raw punches and the rounded ones to decimal and compare. The text of Part 785 is the regulation itself, and it is short enough to read the rounding paragraph in a minute.

Totals past 24 hours are fine, clock times are not

Three videos run 2:14:30, 1:52:10 and 0:58:45. Add them: 8,070 + 6,730 + 3,525 = 18,325 seconds, which is 5:05:25, or 5.09 hours. Nothing about that total needs to fit inside a day.

Push it further: four 8 hour shifts plus 2 hours of overtime is 34 hours, and as a duration that is just 34:00. As a clock time it would read 10:00 on the second day, which is why spreadsheets that format the cell as a time of day show 10:00 and quietly hide the extra day.

The fix in Excel or Google Sheets is a custom format of [h]:mm with the brackets, which tells the program to show accumulated hours instead of a clock reading. If the total is 26 hours, that format shows 26:00, and the calculator shows the same figure with a separate line reading 1 day 2 hours.

When the question is instead how long between two clock times, such as 22:40 to 06:10 the next morning, the time difference calculator is the right tool, since it has to decide which day each reading belongs to.

Three mistakes that show up in spreadsheets

The arithmetic is easy, and the errors are almost always in how the numbers were entered rather than in the adding.

• Typing decimal minutes as decimal hours. 1 hour 50 minutes is 1.8333 hours, not 1.50. Five days of that mistake at 8 hours a day is a 3 hour 20 minute shortfall on the invoice.
• Letting a time format wrap at midnight. A cell formatted as a clock time cannot show 26 hours. Use [h]:mm, or keep the total in decimal hours and format it as a number.
• Adding minutes and then dividing by 100. 150 minutes is 2.5 hours. Dividing by 100 gives 1.5, which is the same wrong answer as the first bullet in a different disguise.

A fourth one is worth a line: mixing units inside one column. If some rows are in decimal hours and others are in hh:mm, no formula can rescue the total. Pick one unit per column and convert at the boundary, which is what the decimal box in the calculator is for.

The National Institute of Standards and Technology keeps the official time and frequency standards for the United States, and the definition it maintains is the same 60 second minute this page assumes. Nothing here depends on time zones or daylight saving, because durations do not care what the clock on the wall says.

Quick answers for common time questions

Short conversions that come up often enough to memorize:

The seconds column is the one people forget. A day is 86,400 seconds, so a task that runs 90,000 seconds has crossed into a second day even though its hour count, 25, looks modest.

For anything longer than a shift, convert to hours once and stay there. Days and weeks only add a division by 24 or 168, and those two constants cover almost every scheduling question that lands on this page.