Calendars and clocks are awkward to do arithmetic on. Months have different lengths, leap years add a day, an hour is sixty minutes rather than a hundred, and daylight saving shifts the offsets twice a year. These tools handle those details so you can get an exact answer for the date or duration you care about.
The two most common errors are counting an interval inclusively when you meant exclusively, and typing minutes as decimals. 7 hours 30 minutes is 7.5 hours, not 7.30. If you're filling in payroll or an invoice, use the Hours to Decimal tool, or the Timecard Calculator, which does the conversion for you.
Age & Dates
Exact age in years, months, and days
Age Difference CalculatorExact gap between two birth dates
Date CalculatorAdd or subtract days from a date
Days CalculatorCount days between two dates
Countdown CalculatorDays until any event
Hours & Timesheets
Hours between two times
Time CalculatorAdd and subtract time
Work Hours CalculatorWeekly work hours total
Timecard CalculatorWeekly work hours & pay
Hours to Decimal CalculatorFor timesheets & payroll
Clock & Zone Conversion
Calendar facts that trip up date arithmetic
| Fact | Detail |
|---|---|
| 30-day months | April, June, September, November |
| February | 28 days, or 29 in a leap year |
| Leap year rule | Divisible by 4, except century years not divisible by 400 |
| Examples | 2000 and 2024 were leap years; 1900 and 2100 are not |
| Weeks in a year | 52 weeks plus one day (two in a leap year) |
That extra day or two is why a salary divided by 52 weeks and a salary divided by 12 months give slightly different hourly figures, and why a biweekly payroll includes two months a year with three pay dates.
For deadlines that matter, state the time zone explicitly and check whether the count is meant to include both end dates. Business-day counts also depend on local public holidays, which no date calculator can know for your jurisdiction.