Add days, weeks, months or years to a date
Get the resulting date after adding a period to a starting date.
Calculator inputs
Results
Enter your values and press “Calculate” to see the result.
In short
- What it calculates
- Get the resulting date after adding a period to a starting date.
- Formula used
New date = start date + amount × unit- Example
- 2026-01-01 + 30 days = 2026-01-31 (Saturday)
Add days to a date
Useful for delivery deadlines, due dates and warranties: enter the starting date and how much you want to add.
Leave the date empty to start from today.
How it works
Adding days or weeks moves along the real calendar. Adding months or years keeps the same day of the month whenever it exists; if it does not, the result snaps to the last valid day.
Formula
New date = start date + amount × unit
30 days ≠ 1 month: choose the unit that matches your deadline
Worked example
2026-01-01 + 30 days = 2026-01-31 (Saturday)
2026-01-01 + 1 month = 2026-02-01
2026-01-31 + 1 month = 2026-02-28, because February has no 31st
Explanation
Months do not all have the same number of days
Adding thirty days to 31 January gives 2 March in a normal year, while adding one month gives 28 February. Neither operation is wrong: they are different things. Contracts usually reason in months and financial calculations in days, and confusing the two shifts the due date.
What happens with the 31st
When you add a month to a 31st and the target month does not have one, the general convention is to fall back to the last available day. From 31 March, one month later is 30 April. Most software and contractual rules follow that criterion, but check the specific document.
Due dates and renewals
Subscriptions, warranties, trial periods and return windows are counted by adding to the start date. Knowing the exact day avoids cancelling one day late, which is when the charge renews automatically.
Subtracting works too
Entering a negative amount gives the earlier date. It is useful for working out when to start a process if you know the deadline and the estimated duration.
Frequently asked questions
What is the difference between adding 30 days and adding a month?
Adding a month keeps the day of the month; adding 30 days moves exactly that far, which may land on a different day of the following month.
Can I subtract instead?
Yes, by entering a negative amount, although the subtract days calculator is clearer.
What happens if I add a month to 31 January?
The usual convention returns the last day of February, because the 31st does not exist that month. Adding 31 days would give a different date.
How do I work out when to start a process?
Subtract the estimated duration from the deadline by entering a negative number of days.
Need to calculate something else?
These tools are often used alongside this calculator.
Subtract days
Find out what date it was a given period before a reference date.
Days between dates
Count the days, weeks and months separating any two dates.
Working days
Count business days while excluding weekends and public holidays.
Age
Work out your age in years, months, days, weeks and hours from your date of birth.
Hours worked
Work out effective working time after breaks, night shifts included.
Days until
Count the days remaining (or elapsed) between today and the date you choose.