Date Calculator
Add or subtract calendar units, or count days between two dates.
About Date Calculator
Use ISO/Gregorian calendar dates between years 0001 and 9999. This calculator works with dates, not timestamps, so daylight-saving changes never shorten or lengthen a calendar day. Years and months are applied together first, clamping to the last valid day of the resulting month; weeks and days follow. January 31 plus one month is February 28 (or 29 in a leap year). A difference excludes the starting date: equal dates give zero, and an earlier end date gives a negative result. All calculations stay in your browser.
Frequently Asked Questions
January 31 plus one month becomes the final day of February. Adding two months in one operation gives March 31. Two separate one-month operations can give March 28 or 29 because each operation clamps separately.
No. Results count every calendar day, including weekends and public holidays.
Calendar years and months have variable lengths. The calendar difference uses whole years, then months, then days in the direction from start to end; total days counts date boundaries. Neither includes both endpoints.