Date Calculator

A date calculator (also called a date arithmetic or date addition calculator) takes a starting date and shifts it forward or backward by a specified amount of time — years, months, weeks, days, or any combination — and tells you the resulting date. The most common use cases are project planning (“what date is 90 days from today?”), contract math (“the lease ends 18 months from signing”), and deadline scheduling (“15 business days from receipt of invoice”). Calendar arithmetic has a few subtle rules: months have unequal lengths (28-31 days), so adding one month to January 31 lands on February 28 (or 29 in leap years), and skipping weekends or public holidays produces a different answer than raw calendar math. This calculator handles both pure calendar arithmetic and business-day arithmetic with bundled holiday calendars for five countries. Pair it with the Working Days Calculator when you specifically need business-day projection, the Date Difference Calculator for the inverse problem (duration between two dates), or the Day of Week Calculator to check the weekday of any computed date.