Date Add or Subtract Calculator
Choose a start date, direction, amount and unit to find a date in the future or past. The result includes the weekday and the actual calendar-day difference.
Add or subtract time from a date
Your dates stay in this browser. They are not sent to our server or saved.
Your result
How month ends and leap years are handled
Days and weeks move by fixed numbers of calendar days. Months and years preserve the original day when possible; otherwise, the result is the last day of the target month. For example, 31 January 2025 plus one month is 28 February 2025, and 29 February 2024 plus one year is 28 February 2025.
The 100th day is not 100 days after
This calculator treats the start date as day zero. Adding 100 days moves forward by 100 days. If the start date is day one, as with a baby's 100th day or a couple's 100-day milestone, add 99 days or use the 100th Day Calculator.
Frequently asked questions
Can I calculate a date in the past?
Yes. Choose Subtract to find a date before the start date.
What happens if I enter zero?
The calculated date is the same as the start date.
Does one month mean 30 days?
No. Months follow the actual Gregorian calendar month, including different month lengths and leap years.
Are the dates I enter saved?
No. The calculation runs in your browser, and your dates are not sent to our server or saved.