Date tools

Each one runs entirely in your browser — nothing you type is sent anywhere — and each page explains the rule that usually trips the calculation up.

Days between two datesCount the days, weekdays and weekend days between any two dates, in either direction.
Age calculatorWork out an exact age in years, months and days, plus the total days lived and the next birthday.
Business day calculatorAdd or subtract business days, skipping weekends and US federal holidays.
Week numberThe ISO 8601 week number for any date, with the week-numbering year.
Leap year checkerWhether any year is a leap year, and why.

How many days in a month

A named month of a named year needs the calendar, not a conversion factor. Pure unit conversions — hours to days, weeks to days — are the same arithmetic everywhere.