Five calculators, no sign-up
Date tools
Checked October 8, 2026 · first publish
Five calculators that run in your browser. Each one shows the result as you type, uses US federal holidays from OPM where they matter, and explains how it counts.
Date calculatorAdd or subtract days, weeks, months or years from any date.Days between datesDays, weeks, months and business days between two dates, or since a date.Business days calculatorCount or add working days, skipping weekends and federal holidays.Day of the yearToday's day number, days left in the year and the ISO week.Birthday countdownDays until your next birthday and your age in days. Your date stays in your browser.
How do these tools count?
All five follow the same rules, written out on the methodology page. The start date is day zero. Business days are Monday to Friday minus federal holidays on their observed dates. Month arithmetic keeps the same day number and stops at the end of a short month. Nothing you type is sent to our server.