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Date & Age Calculator
Find the exact calendar duration between two dates broken down into years, months, and days (with totals in days, weeks, and months), work out someone's age from a birthdate, or add and subtract a duration to a date with correct month-end clamping. Everything runs locally in your browser.
Years/months/days are counted on the calendar: borrowing days from the previous month when the start day exceeds the end day, so 31 Jan + 1 month = 28 (or 29) Feb. Totals (days, weeks, months) are whole-number counts from midnight to midnight. Day-of-week uses your browser's local calendar. Everything runs locally — nothing leaves your browser.