Date Calculator

Date calculations are essential for project planning, contract deadlines, event countdowns, and everyday scheduling. This calculator provides two modes in one tool — find the duration between two dates, or compute a future or past date by adding or subtracting time.

Days between dates: The calculator counts the exact number of calendar days between your start and end dates. Toggle "include end date" to add one day for inclusive counting — useful for rental periods, hotel stays, and billing cycles where both the first and last day count.

Adding and subtracting time: Enter any combination of years, months, weeks, and days to add or subtract from a starting date. Use negative values to go backward in time. Months are added calendar-style — adding 1 month to January 31 gives February 28 (or 29 in a leap year).

Multi-format results: The same duration is shown in multiple units — years/months/days, total days, total weeks, and total hours — so you can pick whichever format you need without doing extra math.

Date facts: Every calculation shows useful context about your dates: the day of the year (1–365), ISO week number, quarter, and whether it falls in a leap year. These details are handy for fiscal planning, payroll periods, and academic calendars.

Leap years and edge cases: The calculator correctly handles leap years, month-end boundaries, and daylight saving time. February 29 in a leap year, adding months to the 31st — all edge cases are resolved using standard calendar rules.