Date & Time Calculators

Count time without mistakes

Leap years, months of different lengths, overnight shifts and public holidays make date math surprisingly error-prone. These calculators handle every edge case — including February 29 birthdays and holidays that fall on weekends — and explain the rules they follow.

Which date and time calculator do you need?

• How old? Exact age in years, months and days with the age calculator; years;months.days for test scoring with the chronological age calculator.
• How long between two dates? The date difference calculator counts days, weeks and months; the business days calculator skips weekends and U.S. federal holidays.
• What date will it be? Add or subtract days, weeks, months or years with the date calculator.
• How many hours? Time between two clock times with time duration; a week of shifts with pay and overtime with hours worked.
• 24-hour time: convert with the military time converter.

Why date math goes wrong

• Months have 28 to 31 days, so “one month later” is ambiguous at month ends. Our calculators move to the last day of the month when needed — one month after January 31 is February 28 or 29.
• Leap years add February 29 every four years, except century years not divisible by 400.
• Inclusive or exclusive counting: Monday to Wednesday is 2 days apart but a 3-day event. Each calculator states which it uses and lets you include the end date when it matters.
• Decimal hours: 7 hours 45 minutes is 7.75 hours, not 7.45 — a common timesheet mistake.
• Holidays that fall on weekends are usually observed on the nearest weekday.

Calculations use the Gregorian calendar and run in your browser, using your device’s date for “today”.