Add or subtract a number of days, weeks, months, or years from a starting date to find the resulting date.
Add/Subtract Date Calculator
LiveResulting date
Enter a start date
Day of week
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How this is calculated
Resulting date = Start date +/- (Amount x Unit)
Example
Starting July 19, 2026, adding 90 days lands on October 17, 2026 (a Saturday). Subtracting 45 days instead lands on June 4, 2026.
Step-by-step guide
- Enter the starting date.
- Choose add or subtract.
- Enter the amount and unit (days, weeks, months, or years) and read the resulting date and day of the week.
Common mistakes
Assuming "add 1 month" always lands on the same day number - if the starting day doesn't exist in the target month (like January 31 plus 1 month), the date rolls over to early the following month.
Manually counting 30 days for "one month" - actual months range from 28 to 31 days, which this calculator handles using true calendar months.
Frequently asked questions
What happens with "add 1 month" from January 31?
Since February doesn't have 31 days, the date rolls forward into early March using standard JavaScript date arithmetic - this is a normal edge case for month-based calculations.
Can I subtract a large number of years?
Yes - the calculator handles any reasonable range of years, both forward and backward from the start date.
Does this account for leap years?
Yes - day and week calculations automatically account for leap years since they work from the actual calendar.
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