Add or Subtract Days
Add or take away days, weeks, months or years from a date, and see exactly which day you land on.
Counting forward on a calendar is quick until the span crosses a month boundary, a leap year or the end of a year — and "90 days from today" is exactly the kind of date that ends up on a contract.
Enter a date, choose how much to move by, and the calculator gives you the result with its day of the week. It also shows the end of that month, the start of the next, and the day number within the year, which is usually the next thing you need.
It is free with no account, and nothing you enter leaves your browser.
How to use it
- Enter the starting date.
- Choose to add or subtract, then enter the amount and the unit: days, weeks, months or years.
- Read the resulting date and its weekday.
- Use the extra figures below if you need them — end of month, start of the next month, and the day-of-year number.
What happens at the end of a month
Adding days or weeks is unambiguous — it is a straight count, and month lengths and leap days are handled for you.
Adding months is not, because months have different lengths. One month after 31 January has to be a date in February, and 31 February does not exist. This calculator clamps to the last day of the target month, so 31 January plus one month is 28 February, or 29 February in a leap year. That matches EDATE in Excel and Google Sheets, and it is the behaviour most contracts assume.
One consequence is worth knowing: clamping is not reversible. Add a month to 31 January and you get 28 February; subtract a month from 28 February and you get 28 January, not 31. That is not a defect in the arithmetic, it is what happens when a date is pushed into a shorter month, and every tool that follows EDATE behaves the same way.
Questions
- What happens when I add a month to the 31st?
- The result is clamped to the last day of the target month, so 31 January plus one month is 28 February (29 in a leap year). This matches Excel’s EDATE function.
- Can I subtract instead of add?
- Yes — switch to subtract, or enter a negative amount. Dates before the start of the year, or before the start of a century, are handled the same way.
- Does it count business days?
- No, this adds calendar days. If you need weekends and public holidays excluded, use the business days calculator, which does the same job on working days only.
- Is there a signup or a limit?
- Neither. It is free, needs no account, and the dates you enter are not sent to our servers.