Add/Subtract Days Calculator
The add/subtract days calculator lets you add or subtract days, weeks, months, or years from any date. Instantly see the resulting date and its day of the week.
Perfect for calculating deadlines, due dates, expiration dates, or planning events. Enter a start date, choose an operation, and specify the amount to get your result.
How it works
The calculator uses calendar arithmetic to add or subtract the specified number of days, weeks, months, or years from the input date. Weeks are converted to days (×7). Month and year additions follow calendar rules, adjusting for varying month lengths.
Use cases
- Calculating project deadlines
- Finding expiration or due dates
- Planning events a specific number of weeks or months ahead
- Determining dates for recurring schedules
Frequently asked questions
How do I add days to a date?
Enter your start date, choose the add operation, and type the number of days. The calculator applies calendar arithmetic and instantly shows the resulting date along with its day of the week. Weeks work the same way and are simply converted to days by multiplying by 7.
What date is 90 days from today?
Set today as the start date, select add, and enter 90 days — the calculator returns the exact calendar date and weekday. This is a common calculation for payment terms, probation periods, and return policies. Because the tool counts actual calendar days, leap years and month lengths are handled automatically.
What happens when I add a month to January 31?
Since February has no day 31, calendar rules adjust the result to the last valid day of the target month, such as February 28 (or 29 in a leap year). This adjustment only applies to month and year operations; adding days or weeks always moves by the exact count. It is a standard convention in date arithmetic.
Does the calculator count business days or calendar days?
It counts calendar days, which include weekends and holidays. If you need a deadline in business days, you would have to skip weekends manually or add extra days to compensate. For most contracts and expiration dates, calendar days are the correct measure.
Can I subtract days from a date to find a past date?
Yes — choose the subtract operation and the calculator moves backward from your start date by the specified days, weeks, months, or years. This is useful for questions like which date was 60 days ago or when a 12-month period began. The result also shows the day of the week for the past date.