CardHours

How We Calculate Hours and Decimal Hours

The rules the time card follows, the payroll documents they come from, and the places where we had to choose.

Updated · sources checked

CardHours works in whole minutes. Every time you type becomes minutes from midnight, every day is a difference of two such numbers, and nothing is rounded until a figure is shown. Where a published document gives the rule, it is quoted with a link. Where none does, the rule is marked Our rule and explained.

Reading the times you type

A time can be typed with or without a colon and with a short or long AM/PM: 9a, 930p, 9:30 p.m. and 21:30 all work, in any case and with any spaces. When you leave the field it is rewritten in full, for example 9:30 PM, and a switch to the 24-hour clock rewrites it as 21:30. That is the conversion payroll offices print: For example: 5:00 PM = 17:00, 4:45 pm = 16:45. (time-sheet instructions published on csusb.edu); the calculator gives 17:00 and 16:45.

Our ruleA time from 1 to 12 without AM or PM on the 12-hour clock is not guessed. The field asks: Add AM or PM (for example 9:15a). Hours 0 and 13 to 23 can only mean one thing, so 17:30 is read as typed.

Our ruleNIST says of these two: This is a tricky question because 12 a.m. and 12 p.m. are ambiguous and should not be used. (NIST, Times of Day FAQs). A time card still needs an answer, so CardHours reads 12:00 AM as midnight at the start of the day and 12:00 PM as noon. The field shows a small midnight or noon label next to these times so you can check.

Worked example, as the calculator shows it:

  • Mon: 12:00 PM → 8:00 PM = 8:00 (480 min ÷ 60 = 8.00 h)
  • Tue: 12:00 AM → 8:00 AM = 8:00 (480 min ÷ 60 = 8.00 h)
  • Total: 480 + 480 = 960 min = 16:00 = 16.00 h

See noon and midnight in the calculator

24:00 is accepted as midnight too and gives the same result as 12:00 AM. ISO 8601 allows both notations, but 00:00 is usually the preferred notation for midnight and not 24:00. (Markus Kuhn's summary of ISO 8601), so the field rewrites it as 12:00 AM. That makes 12:00 AM to 24:00 an error (In and Out are the same time); to enter a full 24 hours, put 12:00 AM to 12:00 PM on one row and 12:00 PM to 12:00 AM on the next.

Hours in one day

A day is an In and an Out, an optional second In and Out, and a break in whole minutes. The hours are the time between each In and its Out, added together, minus the break. A lunch can be typed either way: as a break, or as the gap between two pairs. The csusb.edu instructions give the gap version: Ex. Before Lunch: 8:00 to 12:00 After Lunch: 1:00 to 3:00 Total hours: 6 hours, (time-sheet instructions published on csusb.edu).

A worked example: the Wednesday row of the Hunter College sample payroll timesheet prints 1 hour in the morning, 8 in the afternoon and 9 in total. The calculator gives:

  • Wed: 10:30 AM → 11:30 AM = 1:00, + 12:00 PM → 8:00 PM = 8:00, = 9:00 (540 min ÷ 60 = 9.00 h)
  • Total: 540 min = 9:00 = 9.00 h

Load the Hunter College row in the calculator

Our ruleAn Out earlier than its In is a shift that crosses midnight: the Out is on the next morning. An In equal to its Out is an error (In and Out are the same time.), not 0 or 24 hours.

  • Mon: 10:00 PM → 6:30 AM (next day) = 8:30, − 30 min break = 8:00 (480 min ÷ 60 = 8.00 h)

Which day the hours go on. All hours of a shift stay on the row where it starts. Three payroll offices say the same: For shifts that cross over midnight, the time will be recorded on the day the shift started. (Oregon State University, MyTime timesheet rules); time worked and time away from work with pay are reported on the workday that the shift begins in order to avoid having to split the hours across two days (Duke University Finance, GAP 101.51); Total hours will populate at the top of the timesheet on the day the shift started. (third-shift time entry guidance published on montgomerycollege.edu).

Our ruleThe second In is the first moment at or after the first Out with that clock time, and its Out the first moment after that. So a second pair can run past midnight, or start the next morning, as long as the whole day spans no more than 24 hours. A second pair that overlaps the first by the clock lands on the next day and breaks that limit: In and Out times span more than 24 hours — check for overlapping times.

The third-shift card on montgomerycollege.edu splits a night this way, 10:00pm to 2:00am and 2:30am to 6:30am:

  • Thu: 10:00 PM → 2:00 AM (next day) = 4:00, + 2:30 AM → 6:30 AM = 4:00, = 8:00 (480 min ÷ 60 = 8.00 h)

Try the split night shift in the calculator

A day the calculator cannot count is marked not counted, the field with the problem is outlined, and the other days still add up. The break must be whole minutes from 0 to 1,440, and a break longer than the time worked is an error; a break equal to it gives 0:00.

Hours and minutes, and decimal hours

Each day and total is shown twice: hours and minutes (7:20), and decimal hours, the figure payroll forms ask for. They are the minutes divided by 60, rounded half up to two places, worked out in whole numbers so no step can drift:

hundredths of an hour = (200 × minutes + 60) div 120

That is exactly the chart three universities print for their payroll: the chart published on uhcl.edu, the chart published on norcocollege.edu and the San José State University, Payroll System Decimal Conversion Chart. All 180 printed rows match it. One minute is 0.02, 4 minutes 0.07 and 7 minutes 0.12; cutting the digits off instead of rounding would give 0.01, 0.06 and 0.11. Some employers use a chart in tenths of an hour instead, like the University of Illinois System, Conversion Chart for Minutes to Tenths of Hours; that is a different figure, compared minute by minute on minutes to decimal hours.

Our ruleWeek and period totals are computed from the summed minutes, not by adding the rounded daily decimals. No source we found states either way. Where the two differ, the totals panel says so: Daily decimals are rounded; the total uses exact minutes.

Worked example: three days of 8:00 AM to 3:50 PM with a 30-minute break. Each day is 7.33 decimal hours, and the three added give 21.99; the minutes give:

  • Mon: 8:00 AM → 3:50 PM = 7:50, − 30 min break = 7:20 (440 min ÷ 60 = 7.33 h)
  • Tue: 8:00 AM → 3:50 PM = 7:50, − 30 min break = 7:20 (440 min ÷ 60 = 7.33 h)
  • Wed: 8:00 AM → 3:50 PM = 7:50, − 30 min break = 7:20 (440 min ÷ 60 = 7.33 h)
  • Total: 440 + 440 + 440 = 1,320 min = 22:00 = 22.00 h
  • Pay: 1,320 min × $15.75 ÷ 60 = $346.50

Check the three days in the calculator

Gross pay

With an hourly rate, gross pay is the hours times the rate: All hours worked x hr rate (Duke University Finance, GAP 101.55). The U.S. Office of Personnel Management does the same for a two-week period: Biweekly rates of basic pay are computed by multiplying an employee's hourly rate of basic pay by 80 hours. (OPM fact sheet on the 2,087-hour divisor), with the example $33.84 x 80 hours = $2,707.20. (OPM, How to Compute Rates of Pay). Two weeks of 8:00 AM to 4:30 PM with a 30-minute break at $42.66 give 80:00 hours and $3,412.80.

Our ruleThe pay uses the total minutes, not the rounded decimal hours, and is rounded to the cent once, at the end, the way OPM rounds its hourly rates: Rates must be rounded to the nearest cent, counting one-half cent and over as the next higher cent (e.g., round $18.845 to $18.85). (same OPM fact sheet).

Worked example: 10 minutes at $18.03 is $3.005, which shows as $3.01.

  • Mon: 9:00 AM → 9:10 AM = 0:10 (10 min ÷ 60 = 0.17 h)
  • Total: 10 min = 0:10 = 0.17 h
  • Pay: 10 min × $18.03 ÷ 60 = $3.01

Gross pay = total hours × rate, before taxes and deductions. Overtime is not calculated.

What is rounded

Figures in hours and minutes are exact; decimals have two places. Pay is in dollars and cents. Nothing else is rounded, and every figure on the card, the worked arithmetic, the printout and the CSV file comes from the same functions.

Limits

  • The tool adds up the times you type. It does not know your employer's rounding, work-week or pay rules.
  • Night shifts count on the day they start. Some employers split a shift at midnight; Montgomery College splits only at the end of its work week: The official work week ends on Friday, so the 1st entry should be the start of the shift (In) to 12:00am (third-shift time entry guidance published on montgomerycollege.edu). To match such a card, enter the two parts on two rows.
  • Decimal hours are minutes ÷ 60 to two places; a chart in tenths of an hour gives a different figure.
  • The tool takes the clock-time difference. Across a daylight-saving change the actual time on a night shift differs from it by one hour; adjust that row by hand.
  • Each row is computed on its own: a night shift running into the next row's In is not checked against that row.

We don't calculate overtime, taxes or deductions: the rules depend on your job and your employer.

Sources

All checked .

Changelog

  • : v1 — launch: typed times in 12- or 24-hour form, night shifts counted on the day they start, a second In/Out pair per day, one unpaid break per day, decimal hours as minutes ÷ 60 to two places, week and period totals from exact minutes, gross pay rounded to the nearest cent; sources checked 2026-11-14.