Date Calculator

How it works

Choose a start date, then add or subtract an amount of days, weeks, months or years. Days and weeks are exact: a week is always 7 days, so 30 days after October 8 is November 7 and 28 days is exactly 4 weeks. Months and years follow the calendar instead: the calculator moves the month counter and keeps the day of the month, so 6 months after October 8 is April 8, even though six months can span anywhere from 181 to 184 days. The days between the two dates are shown, so you can see that difference at once.

The end of the month needs one rule, because not every month has a day 29, 30 or 31. When the new month is shorter, the result lands on its last day: January 31 plus 1 month is February 28 (or February 29 in a leap year), and February 29, 2024 plus 1 year is February 28, 2025. Spreadsheets apply the same rule in their EDATE function. Subtracting works the same way backwards, so March 31 minus 1 month is February 28, 2026.

The tool counts calendar days, so weekends and holidays are included. To count only weekdays between two dates, use the days between dates calculator, and to see today's date or the weekday of any date by itself, use what day is it. For an age in years, months and days from a birth date, see the age calculator.

The formula

Internally every date becomes a day number on the Gregorian calendar, so leap days are handled automatically: a span that crosses February 29 contains one more day. Adding 1 year does not always add 365 days. From October 8, 2026 it is 365 days, but from October 8, 2027 it is 366 days because February 29, 2028 falls in between.

The calculator works from January 1, 1753 to December 31, 9999. The American colonies moved from the Julian to the Gregorian calendar in September 1752 (Wednesday, September 2 was followed by Thursday, September 14), so the calculator starts in 1753, where every date follows the Gregorian calendar; older records can use the Julian calendar and would not match.