Date Calculator
Pick a date and add or subtract days, weeks, months or years to find the resulting date and its weekday.
Last updated October 19, 2026
Defaults to today
Result
Wednesday, February 10, 2027
90 days after the start date
Show the work
- Start date: November 12, 2026.
- Operation: add 90 days.
- Years and months are applied first. If the month is shorter, the day moves to the last day of that month.
- Weeks and days are applied next, one day at a time on the calendar.
- The result is Wednesday, February 10, 2027, a Wednesday.
How dates are added and subtracted
result = start date ± years, months, weeks and days
Years and months are applied first as calendar units, then weeks and days are applied as exact days. When the target month is shorter than the start day, the result is clamped to the last day of that month: January 31 plus one month is February 28, or February 29 in a leap year.
The weekday of the result is shown with the date. All dates are calendar dates, so time zones and daylight saving time do not change the answer.
See how we calculate for the formulas, sources and review schedule behind every calculator.
Also useful alongside this calculator: Business Days Calculator and Date To Date Calculator.
Popular answers: Days until a date.
Adding days compared with adding months
A month is not 30 days. Adding 30 days to October 19, 2026 gives Wednesday, November 18, while adding 1 month gives Thursday, November 19, because the calendar month has 31 days there. Use days when a document says “30 days” and months when it says “one month”.
Weeks are exact multiples of 7 days and always land on the same weekday. Adding 12 weeks to Monday, October 19, 2026 gives Monday, January 11, 2027, which is 84 days later. Adding 90 days is 12 weeks and 6 days, so the weekday moves six places along, from Monday to Sunday.
Month ends and subtraction
When the day does not exist in the target month, the result is the last day of that month. January 31, 2026 plus 1 month is February 28, 2026. Subtracting 1 month from March 31, 2026 also gives February 28.
Because of this clamping, adding and subtracting are not always exact opposites. Starting from March 31, going back 1 month gives February 28, but adding 1 month to that gives March 28, not March 31. If you need to return to the original date, keep it and subtract from the original rather than reversing the result.
Leap years and long periods
February 29 exists only in leap years. Adding 1 year to February 29, 2028 gives February 28, 2029, and adding 4 years gives February 29, 2032. Adding 1 year to a normal date lands on the same day and month, such as March 15, 2026 plus 2 years being Wednesday, March 15, 2028.
Common uses are a payment due 30 or 60 days after an invoice, a warranty that runs for 2 years, a trial that ends in 6 weeks and a deadline 12 weeks before an event. For each, enter the start date, choose Add or Subtract, and read the date and weekday. The calculator counts weekends and holidays; use the work hours calculator if you only want working days.
How to use the Date Calculator
- Enter the start date. It defaults to today.
- Choose Add or Subtract.
- Enter the years, months, weeks and days to shift by. Leave unused fields at 0.
- Read the resulting date and weekday, then use Copy, Print or Share.
Worked example
Adding 90 days to Monday, October 19, 2026 gives Sunday, January 17, 2027. Subtracting 3 months from May 31, 2026 gives Saturday, February 28, 2026, because February has no 31st.
| Days added | Date | Weekday |
|---|---|---|
| 7 | October 26, 2026 | Monday |
| 30 | November 18, 2026 | Wednesday |
| 60 | December 18, 2026 | Friday |
| 90 | January 17, 2027 | Sunday |
| 180 | April 17, 2027 | Saturday |
| 365 | October 19, 2027 | Tuesday |
Frequently asked questions
What happens when the month has fewer days?
The result is clamped to the last day of the target month. Adding one month to January 31 gives February 28, or February 29 in a leap year.
Can I subtract instead of add, and does it undo an addition?
Yes. Choose Subtract and enter the amounts. The result is the earlier date, shown with its weekday. After a month-end clamp the two are not exact opposites: March 31 minus 1 month is February 28, and February 28 plus 1 month is March 28.
Why is one month different from 30 days?
Months have 28 to 31 days. October 19, 2026 plus 30 days is November 18, but plus 1 month is November 19. Choose whichever unit your deadline uses.
Does it skip weekends or holidays, and are my dates stored?
No. It adds calendar days, including weekends and public holidays. The calculation runs in your browser and nothing you enter is saved or uploaded.