Date Add Calculator guide
Find the date 30, 60, or 90 days from today, count forward in business days, or work backward from a deadline. Month math follows the same end-of-month rule as Excel.
How the calculator adds time
Date math is not ordinary arithmetic, because the units are uneven. A week is always 7 days, but a month is 28, 29, 30, or 31, and a year is 365 or 366. The calculator handles that by applying units in a fixed order: years and months first, as calendar steps, then weeks and days as exact day counts.
Years are converted to months (1 year = 12 months) and added in one step. If the start day does not exist in the target month, the result snaps to that month's last day. Then weeks are added as 7-day blocks, then days. Subtracting runs the same steps backward.
The month-end rule
Ask a naive date library for January 31 plus one month and you get March 3 (or March 2 in a leap year), because it sets the month to February, sees day 31 does not exist, and overflows into March. That is technically consistent and practically useless.
This calculator clamps instead: January 31 plus one month is February 28, 2026, or February 29 in 2024 and 2028. February 29, 2024 plus one year is February 28, 2025. It is the same behavior as Excel's EDATE function and how most banks count monthly due dates, so results match what you see on statements.
Worked examples
A 90-day window starting October 1, 2026: add 90 days and you land on Wednesday, December 30, 2026. That is a typical return window, a probationary period at a new job, or the length of many US temporary permits.
Six months versus 180 days, starting September 25, 2026: six calendar months lands on March 25, 2027, while 180 days lands on Wednesday, March 24, 2027. One day apart here, but six months runs anywhere from 181 to 184 days, so the gap can reach four days depending on which months you cross. If a contract says "six months", use Months. If it says "180 days", use Days.
Business days: 30 business days after Thursday, October 1, 2026 is Thursday, November 12, 2026. That span also includes two federal holidays (Columbus Day on October 12 and Veterans Day on November 11), so if your office closes on both, the true deadline moves to November 16.
Business days and US holidays
Business-day mode skips Saturdays and Sundays only. It does not know about holidays, because they differ by employer, state, and industry. US federal holidays add 11 days a year: New Year's Day, Martin Luther King Jr. Day, Presidents Day, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving, and Christmas. Banks follow the Federal Reserve calendar, which closes on all 11.
For legal and court deadlines, rules vary. Federal Rule of Civil Procedure 6 counts every calendar day but pushes a deadline that lands on a weekend or legal holiday to the next business day. Check the specific rule rather than assuming business-day counting.
Common mistakes
Counting the start day. Adding 1 day to Monday gives Tuesday. If a notice says "within 10 days" and today counts as day one, enter 9.
Treating 30 days as a month. Across February, 30 days overshoots by two; across a 31-day month it falls short by one. Rent, subscriptions, and loan payments almost always run on calendar months.
Mixing time zones. The calculator works in whole calendar days in your local time, so daylight saving changes in March and November do not shift results by an hour or a day.
Related calculations
To go the other way and count how many days separate two dates, use the days between dates calculator. For hours and minutes rather than dates, use the time duration calculator. And if the date you are calculating is a birthday or an age cutoff, the age calculator gives years, months, and days in one step.
Frequently asked questions
What is the date 90 days from today?
Enter today's date (it is filled in by default), set Days to 90, and read the result. As an example, 90 days after October 1, 2026 is Wednesday, December 30, 2026.
What is Jan 31 plus one month?
February 28, or February 29 in a leap year. When the target month is shorter, the calculator uses its last day, the same rule as Excel's EDATE function. Some basic date code rolls over to March 3 instead, which is almost never what you want.
How do I add business days to a date?
Tick "Count days as business days". The calculator skips Saturdays and Sundays. For example, 10 business days after Friday, September 25, 2026 is Friday, October 9, 2026. Federal holidays are not skipped, so add one day for each holiday in the range.
How do I subtract days from a date?
Switch Operation to Subtract. Use it to find a start date from a deadline, such as the day to mail something that must arrive by a certain date, or the date 180 days ago.
Is adding 1 month the same as adding 30 days?
No. Months are 28 to 31 days long. From February 1, one month lands on March 1 (28 days later in a common year), while 30 days lands on March 3. Leases and billing cycles usually mean calendar months, while notice periods and return windows usually mean days.
Does the result count the start date?
No. Adding 1 day to Monday gives Tuesday. If a rule says "within 30 days including today", subtract one from the number you enter.
Are my dates kept private?
Everything runs in your browser. Nothing you enter is uploaded to a server or stored by us.