Add Days to Date Calculator
Pick a start date, choose how many days to add or subtract, and the resulting date appears instantly — calendar days or business days.
How Adding Days to a Date Works
The calculation is a calendar walk, not a multiplication. Starting from your chosen date, the counter steps one day at a time across the real calendar — which is what makes it fiddly by hand: months have 28, 29, 30 or 31 days, February changes length in leap years, and a long count can cross several month boundaries and a year change. This calculator performs the walk exactly, so November 3, 2026 + 30 days correctly crosses the end of November (30 days) and lands on December 3, 2026.
Two counting modes cover the two ways deadlines are written. Calendar days count every day, and are what "within 30 days" means in most consumer contracts. Business days skip Saturdays and Sundays, and are the language of banking, shipping and office deadlines — turn the option on and the counter reports how many weekend days it stepped over, so you can see exactly why the answer moved. In both modes the start date itself is day zero: adding 1 day to a Monday gives Tuesday.
Worked Example: A 90-Day Notice Period Ending 1 February 2027
- Start: a contract signed on Tuesday, November 3, 2026 allows cancellation with 90 days' notice.
- November contributes the days up to the 30th: 27 days of the count, reaching November 30.
- December's 31 days bring the count to 58 at December 31, and January's 31 bring it to 89 at January 31, 2027.
- One more day — the 90th — lands on Monday, February 1, 2027.
That is the date the notice period completes, and it took three month boundaries and a year change to get there — precisely the kind of count that goes wrong on paper. In business-day mode the same question stretches much further: 90 business days from November 3, 2026 does not complete until Tuesday, March 9, 2027, because 36 of the days stepped over along the way are Saturdays and Sundays. For the reverse question — how many days sit between two dates you already have — the date tools on the Converters & Time Tools shelf include a duration calculator.
Where Day Counts Show Up
Free-look and cooling-off periods (14 or 30 days), invoice terms such as "net 30", trial periods, warranty windows, visa validity, and project plans all come down to this one walk across the calendar. The expensive mistakes are almost never arithmetic — they are the start date counted twice, or a February nobody checked. If your count drives a payment or a filing, run it here, then sanity-check the answer against the weeks figure this page shows: 90 days is 12 weeks and 6 days, never a tidy "three months", and treating months as interchangeable with day counts is how deadlines get missed.
Frequently Asked Questions
How do you add days to a date?
Count forward on the calendar from the start date, skipping into the next month whenever the days run out. Adding 30 days to November 3, 2026 gives December 3, 2026: November has 30 days, so 27 of the added days take you to November 30 and the remaining 3 land on December 3. This calculator does the counting for you, including month ends, leap years and year changes.
Does adding days count the start date itself?
No. Adding 1 day to a Monday gives Tuesday — the start date is day zero, and the count begins with the following day. That matches how deadlines are normally written: 'within 30 days of March 1' means by March 31, not March 30. If you need the start date included in the count (some contracts do this), subtract one day from the number you enter.
What is the difference between calendar days and business days?
Calendar days are every day on the calendar, weekends included. Business days skip Saturdays and Sundays, so 5 business days from a Friday lands on the following Friday, while 5 calendar days lands on Wednesday. Select the business days option above and the calculator skips weekends as it counts — the result panel tells you how many weekend days were passed over.
What date is 90 days from today?
It depends on today's date, which is why this page fills it in for you: the start date is pre-set to today, and the quick buttons include a 90-day jump. As a worked example, 90 days after November 3, 2026 is February 1, 2027 — the count crosses the November (30 days), December (31) and January (31) boundaries on the way.
Can I subtract days instead of adding them?
Yes — enter a negative number, or use the subtract quick button, and the count runs backwards. Subtracting 30 days from November 3, 2026 gives October 4, 2026. Business-day mode works in reverse too: one business day before Monday, November 9, 2026 is Friday, November 6.
How are leap years handled?
Automatically. The calculator uses the real calendar, so February has 29 days in a leap year: February 28, 2028 plus 1 day is February 29, 2028, while the same step in 2026 lands on March 1, 2026. You never need to adjust for leap years yourself.
Is this add days calculator free?
Yes. It is completely free with no signup required, and the calculation runs entirely in your browser — the dates you enter are never uploaded or stored.