Date Calculator
Choose a starting date, then add or subtract any combination of years, months, weeks, and days. The calculator uses real calendar months and leap years, and shows both the resulting date and weekday.
Operation
Resulting date
Choose a starting date to calculate the result.
How to Use the Date Calculator
Choose whether you want to add or subtract time, select a starting date, and enter the number of years, months, weeks, or days. Use zero for any unit you do not need.
The result updates automatically and shows the final calendar date together with its weekday.
Use this calculator when you want to move forward or backward from one known date. To measure the amount of time between two dates instead, use the Days Between Dates calculator.
Adding Days to a Date
Days are added as calendar days, including weekends. For example, adding 30 days to January 1, 2026 gives January 31, 2026.
Subtract works the same way in reverse. Subtracting 10 days from January 5, 2026 crosses into the previous year and gives December 26, 2025.
If you need to count only weekdays or compare two dates, that is a different calculation from adding a fixed number of calendar days.
Adding Months and Years
Months and years use the real calendar rather than fixed day estimates. Adding one month does not mean adding 30 days, because calendar months have different lengths.
For example, January 15 plus one month becomes February 15. January 31 plus one month cannot stay on the 31st because February has fewer days, so the result moves to the final day of February.
Years work the same way. February 29 plus one year becomes February 28 when the target year is not a leap year.
How Month-End Dates Are Handled
When the starting day does not exist in the target month, the calculator uses the last valid day of that month.
For example, January 31, 2024 plus one month becomes February 29, 2024. January 31, 2025 plus one month becomes February 28, 2025.
This keeps month arithmetic predictable and avoids letting the date overflow unexpectedly into the following month.
Order of Date Calculations
When several units are entered together, years and months are applied first. Weeks and days are then added or subtracted from that intermediate calendar date.
That order matters around the ends of months. For example, adding one month and one day to January 31 first moves to the final valid day of February, then adds one additional day.
Using a defined order makes mixed year, month, week, and day calculations consistent.
Leap Years
Leap years contain February 29 instead of ending February on the 28th. The calculator uses the actual Gregorian calendar rules when moving between dates.
A year is normally a leap year when it is divisible by 4, except century years must also be divisible by 400. That means 2024 and 2000 are leap years, while 2100 is not.
Date Calculator vs Days Between Dates
A date calculator starts with one date and moves forward or backward by an amount of time. For example, it can answer what date is 90 days after October 1.
A days-between-dates calculator starts with two dates and measures the interval between them. The two tools solve different problems, even though both work with calendar dates.
Examples
Add 30 days
January 1, 2026 + 30 days
January 31, 2026
Subtract 10 days
January 5, 2026 − 10 days
December 26, 2025
Add one month to January 31
January 31, 2024 + 1 month
February 29, 2024
Add one year to a leap day
February 29, 2024 + 1 year
February 28, 2025
Add weeks
October 1, 2026 + 3 weeks
October 22, 2026
Combine months and days
January 31, 2026 + 1 month + 5 days
March 5, 2026
Frequently Asked Questions
How do I add days to a date?
Select Add, choose the starting date, enter the number of days, and leave the other fields at zero. The calculator shows the resulting date and weekday automatically.
How do I subtract days from a date?
Select Subtract, enter the starting date and number of days, and leave unused units at zero. The calculator moves backward by that many calendar days.
Does one month mean 30 days?
No. Months are treated as calendar months. Their actual lengths are used, so adding one month can represent 28, 29, 30, or 31 calendar days depending on the dates involved.
What happens if I add one month to January 31?
The result becomes the final valid day of February because February does not have a 31st. That is February 28 in a normal year or February 29 in a leap year.
What happens to February 29 when I add one year?
If the following year is not a leap year, the result is February 28 because February 29 does not exist in that year.
Can I add years, months, weeks, and days together?
Yes. Enter values in any combination. Years and months are applied first, followed by weeks and days.
Does the calculator include weekends?
Yes. Days and weeks are ordinary calendar time, so weekends are included.
Can this calculate business days?
No. This calculator adds and subtracts calendar dates. It does not skip weekends or public holidays.
Can I calculate a date in the past?
Yes. Select Subtract and enter the amount of time you want to move backward from the starting date.
How do I find the number of days between two dates?
Use the Days Between Dates calculator instead. This page calculates a new date from one starting date and a time amount rather than measuring the interval between two dates.
Does the calculator handle leap years?
Yes. It uses real calendar dates, including February 29 in valid leap years.
Are my dates sent to a server?
No. The date arithmetic runs locally in your browser.