This calculator adds or subtracts days from a date. Type a start date and a number of days — positive to count forward, negative to count backward — and it returns the resulting calendar date and weekday, rolling over month ends, leap years and year boundaries automatically.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: Gregorian calendar arithmetic, recomputed in code.
How it works
The calculation works in whole calendar days, so it includes weekends and public holidays. Crossing the end of a month or a year is handled for you: adding a day to the last of a month lands on the first of the next, and February gets its 29th day in leap years. This is the right tool for deadlines, due dates, notice periods and "what date is N days from today" questions.
Worked examples
Add across a month end:
Leap day:
Subtract a day across a year:
And because 2024 is a leap year of 366 days, Jan 1, 2024 + 365 days lands on Dec 31, 2024 — not the new year. The calculator returns each result date with its weekday.
Frequently Asked Questions
Enter the start date and the number of days, then add. Jan 1, 2024 + 30 = Jan 31, 2024.
Yes — enter a negative number. Dec 31, 2023 − 1 = Dec 30, 2023.
Enter today and 90. It counts 90 calendar days ahead and shows the weekday.
Yes, every calendar day. For working days only, use a business-days calculator.
Yes. Feb 28, 2024 + 1 = Feb 29; Jan 1, 2024 + 365 = Dec 31, 2024.