📅 Time & Date Calculators

Which time calculator do you need?

Several of these overlap enough to be worth separating clearly. Each one owns a different unit of work.

• Adding or subtracting time. The time calculator does arithmetic on lengths of time and on clock readings: two hours forty-five plus one hour thirty, or nine in the evening plus five hours, including which day that lands on.
• The gap between two moments. The time duration calculator measures elapsed time or time difference across dates and times, and the order you enter them in does not matter.
• One day of hours. The work hours calculator turns clock-in and clock-out into payroll decimals, including split shifts.
• One shift, including overnight. The shift calculator handles a shift that crosses midnight and can apply a differential.
• A whole week or fortnight. The time card calculator totals a pay period and applies overtime per week, which is how the federal rule actually works.
• Two dates. The date calculator counts days between dates or adds and subtracts from one, and the age calculator gives an exact age in years, months, and days.

The mistake that costs the most, and nobody notices

Minutes are sixtieths of an hour. Decimals are hundredths. So a person who works four hours fifteen minutes and writes 4.15 on a timesheet has written 4 hours 9 minutes, not 4 hours 15. The correct decimal is 4.25.

The error is exact rather than approximate: writing mm minutes as hundredths instead of sixtieths is out by precisely 0.4 times the minutes figure, whatever the hours are. Forty-five minutes written as .45 is eighteen minutes short. And it always runs the same direction, so the person doing it is short-changing themselves, every single time, in a way that looks completely correct on the page.

Every tool here that produces hours prints the decimal figure alongside the hours-and-minutes one, so the two can never be confused for each other.

Why calendar arithmetic is harder than it looks

Months are not a fixed length, leap years are not quite every four, and time zones move under you. Counting days by hand works until it does not, and the failure is silent: you get a number, it is just the wrong one. Every date tool here works from the actual calendar rather than an approximation, so February and leap days are handled rather than assumed away.

Daylight saving is the one thing arithmetic cannot fix for you. A shift that spans a clock change is genuinely 23 or 25 hours long, and which one depends on your jurisdiction and the date. We flag it rather than pretending the day was 24 hours.

Overtime is weekly under federal rules

Federal overtime is calculated per week over 40 hours, not per day over 8. That surprises people, because plenty of employers pay daily overtime and several states require it, including California, Alaska, Nevada, and Colorado. Two ten-hour days followed by two five-hour days is 30 hours and no federal overtime, even though two of those days ran long. The time card calculator applies the weekly rule and says so, and your own employer or state may be more generous.