Add Days to Date
Find the date that falls a given number of days, working days, weeks, months or years before or after any date.
🔒 Runs entirely in your browser. Nothing you enter is sent to a server.
Deadlines, notice periods, warranty expiry dates, delivery estimates and medication schedules all need the same calculation: what date is it a certain number of days, weeks or months from now? This calculator does it for any date, forwards or backwards, including business days only.
How to use the date calculator
- Pick the start date. It defaults to a sample date. Change it to today or any date you need.
- Choose Add or Subtract.
- Enter the amount.
- Choose the unit: days, business days, weeks, months or years.
The result shows the full date with its weekday, the ISO date, the number of calendar days in between, the ISO week number and the day of the year.
How each unit works
- Days: adds exactly that many calendar days. Leap days are included automatically.
- Weeks: adds 7 days for each week.
- Months: moves the same day number into the target month. If that day does not exist, such as 31 February, it uses the last day of the month.
- Years: adds 12 months. 29 February plus one year gives 28 February.
- Business days: steps forward or back one day at a time, counting only Monday to Friday.
Result (days) = Start + n × 1 day
Result (weeks) = Start + n × 7 days
Result (months) = same day, n months later (clamped to the month's last day)Worked examples
Starting from Wednesday 28 October 2026:
- +90 days → Tuesday 26 January 2027. That is in ISO week 4 and is the 26th day of 2027.
- −90 days → Thursday 30 July 2026.
- +30 business days → Wednesday 9 December 2026, which is 42 calendar days later because six weekends fall in between.
- +6 months → Wednesday 28 April 2027.
- +1,000 days → Tuesday 24 July 2029.
And an end-of-month case: 31 January 2026 + 1 month → Saturday 28 February 2026.
Common uses
| Need | Example |
|---|---|
| Contract or notice period | 30 days from the date notice was given |
| Return or refund window | 14 or 30 days from delivery |
| Payment terms | Net 30 or net 60 from the invoice date |
| Probation period | 3 or 6 months from the start date |
| Visa or stay limits | 90 days from arrival |
| Project planning | 20 business days from kickoff |
Tips and pitfalls
- Check whether the start day counts. This calculator does not count the start date. If your rule says “within 30 days, including today”, subtract one.
- Holidays are not excluded. For legal or banking deadlines, check the local holiday calendar and add a day for each holiday in the period.
- Months and weeks differ. “One month” from 1 February is 1 March (28 days), but from 1 March it is 1 April (31 days).
- Some deadlines move off weekends. Many official deadlines that land on a Saturday or Sunday move to the next working day. Check the rules that apply to you.
- Leap years are handled. Adding 365 days across a 29 February lands one day earlier in the calendar than adding one year.
Everything is calculated in your browser using calendar dates, so time zones and daylight saving changes never shift the result.
Frequently asked questions
What date is 90 days from today?
Set the start date to today, choose Add, enter 90 and pick Days. For example, 90 days after 28 October 2026 is Tuesday 26 January 2027.
How are business days counted?
Business days skip Saturdays and Sundays. The start date itself is not counted. Public holidays are not skipped, because they differ by country and region, so add one extra day for each holiday in the period.
What happens when I add a month to 31 January?
February has no 31st, so the result is the last day of February, the 28th or the 29th in a leap year. The calculator always moves to the last valid day of the month instead of spilling into the next month.
Is adding 4 weeks the same as adding a month?
No. Four weeks is always exactly 28 days, while a month is 28 to 31 days. Use weeks for fixed-length periods, such as a 4-week notice period, and months for calendar periods, such as a monthly billing date.
What is the ISO week number?
ISO 8601 numbers the weeks of the year starting on Monday, with week 1 being the week that contains the year's first Thursday. Many businesses in Europe and Asia plan by these week numbers.