Time Card Calculator

Most arguments about a paycheck are not about multiplication. Nobody disputes that eight hours plus eight hours is sixteen. The quarrels start at the edges: which week a Saturday night belongs to, whether a lunch counted, how long a shift lasted on the night the clocks went back, and whether the time clock’s rounding quietly shaved a few minutes off every day. A time card is only as honest as the way it handles those boundaries.

The federal rules on hours and overtime are short enough to read in an afternoon, and most of what they say is about boundaries. They define the period hours are added up in, the breaks that count, and how much rounding is tolerated. What they do not do is the arithmetic for you, and that arithmetic is easy to get subtly wrong.

The week that is not a calendar week

Overtime under the Fair Labor Standards Act is measured per workweek, and the regulation defines that word with care. A workweek is a fixed and regularly recurring period of 168 hours, seven consecutive 24-hour periods. It does not have to match the calendar week. It may start on any day and at any hour, and once an employer sets the start it stays put, whatever the schedule does. An employer may move it only for good, and not to dodge overtime.

That freedom is the first trap. A plant whose workweek starts at 7:00 on a Wednesday morning has weeks that cut straight through a Wednesday shift. Spreadsheets tend to group hours by the date a shift began, which is a calendar habit, not the legal unit. The ISO 8601 standard that most software follows numbers its weeks from Monday, which is a third answer again. None of these is wrong as a way to label dates. Only one of them is the period overtime is counted in.

The second trap is averaging. Each workweek stands alone. A worker with 30 hours one week and 50 the next is owed overtime for the second week, even though the two weeks average exactly 40 hours. The regulation says this holds whether the person is paid by the day, the week, every two weeks or the month. A biweekly pay period does not create a two-week workweek.

The 40-hour line arrived with the Fair Labor Standards Act of 1938. The Department of Labor still states it plainly: hours over 40 in the workweek, at not less than one and one-half times the regular rate.

So a shift that crosses the workweek boundary has to be cut at that exact minute. A Saturday night shift that runs from 22:00 into Sunday morning, under a workweek that starts at Sunday 00:00, puts two hours in one week and the rest in the next. Those two hours may decide whether either week reaches 40.

Breaks that count and breaks that do not

Short rest periods are work. The regulation describes rest periods of 5 minutes to about 20 and says they must be counted as hours worked. The Department’s fact sheet puts it as usually 20 minutes or less.

Meal periods are different. A bona fide meal period is not worktime, but only when the employee is completely relieved from duty for the purpose of eating a regular meal. Ordinarily 30 minutes or more is long enough, and a shorter period may be long enough only under special conditions. A clerk who must eat at the desk, or a machine operator who must stay at the machine, is working while eating, and that time counts.

Two practical rules follow for a time card. A rest break entered as unpaid is a mistake, however short it was. And a meal break needs both a length and a fact behind it: the person was free. A calculator can test the length against the threshold you choose, and it can flag a 20-minute “meal” as something that does not ordinarily qualify. It cannot see whether the person was really relieved from duty.

Rounding punches, and who it favours

Time clocks are not required, and many workplaces never used them. Where they are used, the regulation accepts a long-standing habit: recording starting and stopping times to the nearest 5 minutes, or the nearest tenth or quarter of an hour. That gives three increments, 5, 6 and 15 minutes, and the regulation accepts them on one condition. Rounding is tolerated when it averages out, and is not tolerated when, over a period of time, it fails to pay people for all the time they actually worked.

That condition turns rounding from a convenience into something that has to be checked. To the nearest quarter hour, a punch at 8:07 becomes 8:00 and a punch at 8:08 becomes 8:15. Each individual punch moves by at most seven minutes, in one direction or the other. The question the rule asks is about the sum. If staff habitually punch in a few minutes early and out a few minutes late, nearest-quarter rounding will take those minutes away almost every day.

The only way to know is to keep both numbers: the minutes between the actual punches and the minutes after rounding, added up over the period, with the difference shown and signed. A net of zero, or a net in the worker’s favour, is the pattern the regulation contemplates. A steady net loss is the pattern it forbids.

Night shifts and the hour that appears or vanishes

Twice a year, in most of the United States, a night shift is not the length the clock says. Daylight saving time begins at 2:00 a.m. on the second Sunday of March, when the clock skips ahead to 3:00, so that day has one hour less. It ends at 2:00 a.m. on the first Sunday of November, when 1:00 to 2:00 is repeated and the day lasts 25 hours from midnight to midnight. Other countries change on other dates, and in the Southern Hemisphere the change runs the other way.

A night worker on the fall-back shift works an hour that the wall clock does not show. Subtracting the clock reading at the end from the clock reading at the start gives a number that is one hour short. In the spring it gives a number that is one hour long. Both errors land on exactly the people who already work the least convenient hours.

The fix is old and well tested. Convert every punch to an absolute instant using the rules for the place it happened, then subtract instants. The rules for every place live in the public-domain time zone database, which records the history of local time for representative locations and is updated when governments change their clocks. Browsers expose it through Intl.DateTimeFormat, which accepts a zone name such as Australia/Sydney or America/Chicago. Two awkward cases remain, and they should be flagged rather than guessed: a punch typed inside the skipped spring hour names a time that never existed, and a punch inside the repeated fall hour names a time that happened twice.

Take a fictional night worker in Chicago with a workweek starting Sunday at 00:00. On Saturday, 31 October 2026, the punches read 21:53 in and 06:34 out, with a 30-minute meal at 02:00. The clock face shows 8 hours 41 minutes between the punches. Because the clock fell back at 2:00 that night, the time that really passed is 9 hours 41 minutes.

Round both punches to the nearest quarter hour and they become 22:00 and 06:30: 9 hours 30 minutes of real time. Take off the meal, which is long enough to be unpaid, and the shift is 9.00 hours worked. The workweek boundary at midnight then splits it. Two hours, 22:00 to 24:00 on Saturday, belong to the week that is ending. The remaining 7.00 hours belong to the new week, because 00:00 to 06:30 on that Sunday lasted 7 hours 30 minutes.

Add five more nights in the same week, one of them a long night with a 20-minute meal that is too short to deduct, and that workweek reaches 49.00 hours: 40.00 straight time and 9.00 overtime. At a multiplier of 1.5 that is 53.50 straight-time hour equivalents, which any hourly rate then multiplies. Over the six shifts the rounding took 7 minutes more than it gave, a small sum that the regulation still asks someone to notice. Every one of these numbers can be reproduced on this page, because the example loads with it.

Keeping a record both sides can check

The Department of Labor does not prescribe a form. Employers may use a time clock, a timekeeper, or workers writing their own times, and any plan is acceptable as long as it is complete and accurate. The records must include the time and day the workweek begins, hours worked each day and total hours each workweek, and time cards are among the records kept for two years.

That list is a good design brief for any time card. Show the workweek start. Show each day and each week, and show where a shift was cut. Keep the punches as typed beside the rounded ones. When a file moves between systems, a plain format such as the comma-separated values described in RFC 4180 keeps every row readable by the next program without guesswork about quoting.

There are limits to what any calculator can settle. It cannot tell whether a job is exempt from overtime, whether waiting or on-call time was work, or whether bonuses and other pay belong in the regular rate, which the regulation defines as total pay for the week divided by the hours actually worked. It does not know which state or city rules apply. The federal Act itself does not require premium pay for weekends or days of rest as such, so any daily or seventh-day threshold has to come from the rule being applied. Those questions belong to the employer, the worker and, when they disagree, someone qualified to advise them.

What a calculator can do is make every minute visible. When both sides see each punch as an instant, each cut and the net rounding, the argument moves from arithmetic to rules. That is a better argument to have.