Add Months to a Date Calculator
Enter a start date and a number of months. Use a negative number to go back in time.
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Formula
new month = start month + months (the year rolls over after December)
new day = min(start day, last day of the new month)
So the day is kept when it exists, and otherwise moves back to the end of the month.
Worked example
31 January 2024 + 1 month: the new month is February 2024, which has 29 days, so the day becomes min(31, 29) = 29. The result is 29 February 2024. In 2023, February has 28 days, so 31 January 2023 + 1 month is 28 February 2023.
Frequently asked questions
What is 31 January plus 1 month?
There is no 31 February, so the result is the last day of February: 29 February 2024 in a leap year, or 28 February 2023 in a common year.
How are months added?
The month number moves forward and the day of the month is kept. 15 January 2024 plus 14 months is 15 March 2025.
Can I subtract months?
Yes, enter a negative number. 31 March 2024 minus 1 month is 29 February 2024, because February has no 31st.
Why is the number of days between not constant?
Months have 28 to 31 days. 15 January 2024 plus 14 months is 425 days later, while 31 January 2023 plus 1 month is only 28 days later.