How to use the date calculator
- Choose a start date. It defaults to today.
- Pick Add or Subtract.
- Enter any mix of years, months, weeks and days.
- Read the resulting date, its weekday and how many calendar days away it is.
Formula
1. New month = start month + (years x 12 + months). If the day does not exist, use the last day of that month.
2. Then add or subtract (weeks x 7 + days) calendar days.
Months are applied first so that month ends behave predictably: January 31 plus 1 month is February 28 (or 29 in a leap year), never March 3.
Worked examples
Plus 90 days: October 12, 2026 plus 90 days is Sunday, January 10, 2027.
Month end: January 31, 2026 plus 1 month is February 28, 2026. In 2028, a leap year, January 31 plus 1 month is February 29.
Mixed: October 12, 2026 plus 1 year, 1 month, 1 week and 1 day: first November 12, 2027, then 8 more days, Saturday, November 20, 2027.
Subtract: October 12, 2026 minus 12 days is Wednesday, September 30, 2026.
Leap days
Adding a year to February 29 lands on February 28 in a common year, because there is no February 29. Adding four years to February 29, 2024 gives February 29, 2028.
Typical questions this answers
What date is 30, 60 or 90 days from today, when does a 6-month warranty end, what was the date 100 days ago and when is my due date 40 weeks after a given date. For business-day deadlines, use the business days calculator instead, because calendar days include weekends.
Assumptions and limits
- Calendar arithmetic on dates only. Time of day and time zones are ignored.
- Results must fall between the years 1000 and 9999.
- Weekdays are calculated for the Gregorian calendar.
Frequently asked questions
What is 90 days from today?
Leave the start date at today, choose Add and enter 90 days. The date and weekday appear immediately.
What is 6 months from a date?
Enter 6 in months. If the day is the 31st and the target month is shorter, the last day of that month is used.
Can I subtract business days?
Use the business days calculator, which can move backward and skips weekends and holidays.