About the Date Calculator
Date Calculator answers questions such as what the date will be in 90 days, what the date was 6 months ago, or when a 12-week programme ends. Pick a start date, choose Add or Subtract and enter any mix of years, months, weeks and days. The tool shows the resulting date in full with the weekday, the number of days between the two dates, the day of the year, the ISO week number and whether the year is a leap year. Months are handled the way calendars work: adding one month to the 31st lands on the last day of a shorter month. The start date is filled with today's date and can be changed. Calculations are made in your browser and no date is sent anywhere.
Updated September 2026
How to use the Date Calculator
- 1Pick a start date. It begins as today and you can change it.
- 2Choose Add to go forward or Subtract to go back.
- 3Type the years, months, weeks and days. You can use one box or several.
- 4Read the new date in the big box, with its weekday.
- 5Check the extra facts below: days between, day of the year, week number and leap year.
When a date calculator helps
Plenty of everyday tasks come down to a date plus or minus some time. You may want the end date of a 90-day notice period, the day a 30-day return window closes, the due date for a payment that is due in 45 days, the finish of a 12-week training plan or the date of a follow-up appointment in 6 months. Counting on a calendar is slow and mistakes are easy, especially across month ends and leap years.
This calculator does the counting for you and shows the weekday at once, so you can see whether the date falls on a weekend and plan for it.
How the sums are done
- Years and months are added together as months and applied first.
- If the target month is shorter, the result becomes that month's last day.
- Weeks are turned into days (7 each) and added with the days.
- Subtracting works the same way in reverse.
Reading the extra facts
The days between line shows how many calendar days separate the start date from the result, which is handy when you were given months but need a day count, such as for interest or a contract. The day of the year is useful for planning and for some scientific and business uses, and the ISO week number is used in many companies for schedules and production plans.
The leap year line explains why February may have 29 days in the result year. A year is a leap year if it can be divided by 4, except that century years must be divisible by 400, so 2000 was a leap year and 1900 was not.
Related date tools
Days Between Dates counts the gap between two dates you know, Age Calculator gives exact years, months and days since a birth date, and Hours Calculator adds up time worked. Pregnancy Due Date Calculator estimates a due date from the last period, Time Zone Converter finds the same moment across places and Countdown Timer counts down to an event.
Features
- Add or subtract years, months, weeks and days together
- Full result with weekday
- Days between the start and the result
- Day of the year and ISO week number
- Leap year check
- Month-end handling that matches calendars
- Copy the result in one tap
- Runs in your browser
Frequently asked questions
What date is 90 days from today?
Leave the start date on today, choose Add, clear the days box and type 90. The result appears at once with its weekday. Ninety days is about three months, but because months have different lengths it can land a day or two either side of the same date three months on.
How does the tool add months to dates like the 31st?
It moves the month first and, if the new month is shorter, uses its last day. Adding one month to 31 January gives 28 February in a common year and 29 February in a leap year. Adding one month to 30 April gives 30 May.
Are weeks and days counted from the same date?
Yes. Years and months are added first, then weeks and days are added as a plain number of days. Two weeks and three days is treated as 17 days. If you enter only days, the result is the same as counting on a calendar.
Can I go back in time?
Yes. Choose Subtract and enter the amount. To find the date 6 months and 10 days ago, choose Subtract, type 6 in Months and 10 in Days. The tool works for years 100 to 9999.
What is the ISO week number?
ISO 8601 weeks start on Monday, and week 1 is the week that contains the first Thursday of the year. Because of this, the first days of January can belong to week 52 or 53 of the previous year, and the last days of December can belong to week 1 of the next.
Does it count business days or skip weekends?
No, it counts every calendar day. To skip weekends and holidays, use Working Days Calculator. To find the number of days between two dates you already know, use Days Between Dates.
Does the time zone change the answer?
No. The tool works with calendar dates only, in a fixed way, so the result does not depend on the time zone of your device or on daylight saving changes.