Time & Hours Calculator

This one page replaces separate "time", "hours", "duration" and "time card" tools, because they all do the same arithmetic. It has five modes:

1. Add / subtract time. Sum durations like 1:12:45 + 0:58:30, or subtract a break from a shift.
2. Hours between two times. Enter a start and an end date and time; overnight shifts and daylight saving changes are counted as real elapsed time. The result also shows the calendar difference in years, months and days, plus the total in days and weeks.
3. Date + duration. Add or subtract years, months, days, hours, minutes and seconds to a date and time to find a deadline or a start date.
4. Convert units. Turn seconds, minutes, hours, days, weeks, months or years into any other of those units, e.g. 7.75 hours is 465 minutes.
5. Weekly timesheet. Enter each day's punches, and mark each break as paid (a short rest break) or unpaid (a meal break). You can apply 5-, 6- or 15-minute rounding to the punches and choose the day and hour your workweek starts. The sheet shows hours over 40 in that workweek. For a schedule without punch times, a quick total multiplies work days by hours per day.

The sections below explain the rules behind each setting, so you can defend the number you get.

Why hours don't add like ordinary numbers

Clock time is counted in mixed bases: 60 seconds to a minute, 60 minutes to an hour, 24 hours to a day. That is why a spreadsheet goes wrong when someone types 7.50 meaning "7 hours 50 minutes". 7 h 50 min + 1 h 25 min is 9 h 15 min (9.25 decimal hours), not 8.75.

Dividing the day into non-decimal units is very old. The National Institute of Standards and Technology's history of timekeeping describes how the Sumerians, some five thousand years ago, divided the day into 12 periods (each equal to two of our hours) and split each period into 30 parts of about four of our minutes. It also describes an Egyptian shadow clock from around 1500 BCE that split the sunlit day into 10 parts plus two "twilight hours". Because the clock is still base-60, payroll has to translate between clock minutes and decimal hours.

Minutes to decimal hours (decimal = minutes / 60):

To go back, multiply the decimal part by 60: 0.4 hours x 60 = 24 minutes.

Which breaks to subtract, and which to leave in

This is the setting that most changes the answer. Under the federal Fair Labor Standards Act (FLSA), the two kinds of break are treated differently.

The U.S. Department of Labor's Fact Sheet #22 on hours worked under the FLSA explains the difference:

• Rest breaks of short duration, usually 20 minutes or less, are customarily paid and must be counted as hours worked.
• Bona fide meal periods, typically 30 minutes or more, generally need not be paid, but only if the employee is completely relieved from duty. An employee who eats at the desk while answering the phone is still working.

Worked example. A shift runs 7:00 AM to 3:30 PM, with a 30-minute lunch away from the desk and two 15-minute rest breaks.

• Elapsed time is 8 h 30 min.
• Subtract only the lunch: 8.00 hours worked.
• A timesheet that also subtracts the two rest breaks records 7.50 hours. That is half an hour short every day, or 2.5 hours over a five-day week.

In the calculator, enter every break but mark only true meal periods as unpaid.

Federal law does not require employers to offer lunch or coffee breaks at all, but some states do. California, for example, requires a half-hour meal period when the workday runs more than 5 hours, with limited exceptions. Check your state's rules if breaks are being skipped.

24-hour shifts follow their own rule, which matters for round-the-clock roles such as on-site residential staff. Fact Sheet #22 says:

• An employee on duty for less than 24 hours is working even if allowed to sleep when not busy.
• For duty of 24 hours or more, employer and employee may agree to exclude a bona fide, regularly scheduled sleep period of up to 8 hours, if adequate sleeping facilities are provided. No reduction is allowed unless the employee gets at least 5 hours of sleep.

So an agreed 8-hour sleep period turns a 24-hour tour into 16 hours worked. If calls leave the employee fewer than 5 hours of sleep, the full 24 hours count.

Rounding punches: what the federal rule actually allows

Some time clocks round punches. The rule is 29 CFR 785.48, the Labor Department regulation on time clocks and rounding. It recognizes the long-standing practice of recording starting and stopping times to the nearest 5 minutes, or to the nearest tenth or quarter of an hour. It accepts that practice only if, over time, it does not result in failing to pay employees for all the time they actually worked.

Two practical consequences follow.

1. "Nearest" means symmetric. With quarter-hour rounding, a punch 1 to 7 minutes after a quarter-hour rounds back, and 8 to 14 minutes after rounds forward. So 7:52 records as 7:45, and 7:53 records as 8:00. This is where the "7-minute rule" comes from. A policy that always rounds clock-ins forward and clock-outs back is not rounding to the nearest increment.

2. Symmetric rounding can still be one-sided in practice. Rounding only "averages out" when punch times scatter randomly around the shift boundaries, and real punches often don't.

• Take a worker who is expected on the floor early. They clock in at 7:55 and out at 5:05 every day.
• Quarter-hour rounding records 8:00 to 5:00: 9 h 00 min against 9 h 10 min actually on the clock.
• That is 10 minutes lost per day, or 50 minutes over a five-day week, even though every single punch was rounded to the nearest quarter-hour.

The timesheet mode shows actual and rounded totals side by side, so you can check whether a rounding policy is neutral for a specific person over a full pay period. That mirrors the regulation's test.

Round each punch, not the day's total. The regulation describes rounding starting and stopping times, and rounding the total gives a different result.

The tenth-of-an-hour increment the regulation mentions is also the 6-minute unit that many professional-services firms bill in. For example, 2 h 38 min is 2.63 hours, which records as 2.6 (2 h 36 min) when rounded to the nearest tenth.

Overnight shifts and daylight saving time

A shift that crosses midnight needs a date on both ends. Otherwise 10:00 PM to 6:30 AM looks like a negative number. Twice a year the clock itself also changes.

NIST, an official timekeeper for the United States, publishes its daylight saving time rules for the United States:

• DST begins at 2:00 a.m. local time on the second Sunday of March, when clocks skip ahead to 3:00.
• It ends at 2:00 a.m. on the first Sunday of November, when the 1:00 hour repeats.
• In 2026 those dates are March 8 and November 1.
• DST is not observed in Hawaii, American Samoa, Guam, Puerto Rico, the Virgin Islands, or the state of Arizona, with the exception of the Navajo Indian Reservation, which does observe it.

Wall-clock arithmetic gets these nights wrong:

A real-world case. A nurse on a 7:00 PM to 7:30 AM night shift with a 30-minute relieved meal break normally works 12.0 hours. On the night of October 31 to November 1, 2026, the same shift is 13.0 hours worked, because the 1:00 AM hour happens twice.

The calculator uses the dates you enter and your time zone, and it reports elapsed time, which is the time the worker actually spent on the job.

Weekly totals and overtime

Federal overtime is counted per workweek, not per day. The Labor Department's overtime fact sheet (Fact Sheet #23) sets out the rules:

• Covered, non-exempt employees must be paid at least time and one-half for hours over 40 in a workweek.
• The workweek is a fixed, regularly recurring period of 168 hours, meaning seven consecutive 24-hour periods. It can start on any day and at any hour.
• Averaging hours over two or more weeks is not permitted.
• The FLSA does not require overtime for work on Saturdays, Sundays or holidays as such.

Two consequences for your timesheet:

• Four 10-hour days total 40 hours, so there is no federal overtime that week.
• 45 hours one week and 35 the next means 5 overtime hours in the first week, even though the two weeks average 40.

Set the workweek start in the calculator to match your employer's, because a Wednesday-to-Tuesday week can total differently from a calendar week. Hours count in the workweek in which they are worked, so a shift that runs across the workweek start is split between the two weeks: with a week starting Sunday at midnight, a Saturday 10:00 PM to Sunday 6:00 AM shift puts 2 hours in the old week and 6 in the new one.

State law can be stricter. California's general overtime rules, for example, require time and one-half for hours worked over eight in a workday as well as over 40 in a workweek. Turn on the daily rule only if it applies to you.

Keep the record

Under the Labor Department's recordkeeping rules (Fact Sheet #21):

• Employers must record the hours worked each day and the total hours worked each workweek.
• Time cards must be kept for two years, and payroll records for at least three.
• Any timekeeping method is acceptable, whether a time clock, a timekeeper, or employees writing down their own times, as long as the record is complete and accurate.

If you track your own hours, write down each day's in and out punches and breaks as you go, and copy the timesheet mode's daily and weekly totals into that record next to your pay stubs. The timesheet's Share link saves its settings (rounding, workweek start, overtime rules, pay rate and overtime multiplier), not the punches themselves.

A short history of the time card

The punch clock began as a cost-cutting device. U.S. Letters Patent No. 393,205, dated November 20, 1888, went to Willard L. Bundy of Auburn, New York, for an improved "Time-Recorder". Its stated purpose was to have factory and shop employees record the time they arrived at work, saving the expense of the watchmen or timekeepers who had done it by hand. The gap between recorded time and time actually worked is still what the rounding rule above polices.

Quick answers

This page explains federal (FLSA) rules for general information. It is not legal advice. State law, union contracts and exemptions can change the answer for a specific job.

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