Date & Time
Date arithmetic looks trivial and is not: month lengths vary, leap years have an exception to their exception, and "working days" depends on which calendar you mean. These tools state the convention they use, which is the part that makes two date calculators disagree.
Age
Age CalculatorAge in years, months and days, with the next birthday and the day of the week. It borrows the way people do when counting rather than dividing days by 365.25, which drifts and produces a fraction nobody uses.Age Difference CalculatorThe gap between two birth dates in years, months and days. It borrows the way people do when counting, rather than dividing days by 365.
Dates
Date Difference CalculatorDays between two dates, in calendar units and working days. Whether the end date counts is an input rather than a convention, because that single choice is behind most off-by-one disputes in notice periods and contracts.Add or Subtract Days CalculatorAdd or subtract a period from a date. Months are added before days and clamp at month end, which is why adding one month to 31 January gives 28 February rather than 3 March.Days Until Date CalculatorDays until a date, with the working days separated out. Counting at UTC midnight means a range crossing a daylight saving change is still a whole number of days.Week Number CalculatorWeek number under both the ISO and US conventions, which frequently disagree. ISO weeks start Monday and can put early January in the previous year; the US convention starts Sunday and never does.Day of the Week FinderThe day of the week for any date, with the ISO week number. ISO weeks start on Monday and week one contains the first Thursday, so early January can belong to the previous year.Leap Year CheckerWhether a year is a leap year, including the century rule that catches people out. 1900 was not a leap year and 2000 was.
Time
Time Duration CalculatorDuration between two times with a break deducted, in both clock and decimal form. Decimal hours is what payroll wants, and 8 hours 15 minutes is 8.25 rather than 8.15.Time Addition and Subtraction CalculatorAdd or subtract two durations. Converting to seconds first avoids the carrying errors that come from working in a base-sixty system by hand.Military Time ConverterConvert between 12-hour and 24-hour time. Midnight and noon are the cases that trip people: 12 AM is 00:00 and 12 PM is 12:00, which feels backwards.Decimal Hours ConverterDecimal hours against hours and minutes. Fifteen minutes is a quarter of an hour, so 8:15 is 8.25 decimal hours, and entering 8.15 on a timesheet underpays by six minutes.
Business
Business Days CalculatorBusiness days between two dates, or the date a number of business days lands on. A thirty day deadline and thirty working days differ by nearly two weeks, and contracts that fail to say which they mean produce exactly that dispute.Timesheet and Hours Worked CalculatorA weekly timesheet with breaks deducted and overtime split out. Breaks come off before the overtime threshold is tested, which is what decides whether a week crosses it, and 8 hours 15 minutes is 8.25 decimal hours rather than 8.15.
More
Retirement Date CalculatorRetirement date and how far away it is, in years, months and working days. The working-day figure is the one that makes it feel real.Anniversary and Milestone CalculatorWhen a day, week or month milestone falls. Ten thousand days is about twenty-seven and a half years, which is a better-observed anniversary than most.