Add or Subtract Days Calculator

What this calculator does, and how it's different from Date Difference

This calculator answers "what date is 30 days from now?" — starting from a date, it adds or subtracts a number of days and tells you the resulting calendar date. This is the reverse of the Date Difference Calculator, which instead takes two dates and tells you how many days apart they are.

How it's calculated

The calculator takes your starting date and directly adds or subtracts the number of days you enter, correctly accounting for varying month lengths and leap years using standard calendar-date arithmetic — no manual counting of days-in-month required.

Worked example

Starting from September 4, 2026 and adding 30 days lands on October 4, 2026 — because September has 30 days, adding 30 days moves the date forward exactly one full month plus zero extra days in this particular case. The calculation handles month-length differences automatically, so the same +30-day operation from a 31-day month gives a different day-of-month in the result.

Practical use cases

• Finding a deadline that's a fixed number of days from today (e.g. "payment due in 45 days")
• Working out a return-by or expiry date from a purchase date
• Calculating a follow-up date for a medical appointment or subscription renewal
• Finding a date a certain number of days in the past, for record-keeping or scheduling

Limitations

This calculator adds or subtracts calendar days, not business days — every day counts, including weekends and holidays. If you need to skip weekends, use the Working Days Calculator instead.

Frequently asked questions