🗓️ Month Calculator
Add or subtract any number of months from a date and get the correct resulting calendar date — including the tricky end-of-month cases most simple calculators get wrong.
Add or subtract months from a date — end-of-month dates are clamped correctly.
How the Month Calculator works
When adding months pushes the day-of-month past the end of the target month (like January 31st plus one month), the result is correctly clamped to that month's last valid day — so you get February 28th (or 29th in a leap year), not an invalid date.
Step-by-step calculation
- 1Pick the start date.
- 2Enter months to add or subtract.
- 3Month-end days are clamped to the target month.
- 4Read the resulting date.
Worked example
January 31, 2026 plus 1 month is February 28, 2026. August 15, 2026 plus 6 months is February 15, 2027.
Month Calculator examples
| Months added | New date |
|---|---|
| 1 | February 28, 2026 (Saturday) |
| 3 | April 30, 2026 (Thursday) |
| 6 | July 31, 2026 (Friday) |
| 12 | January 31, 2027 (Sunday) |
| 18 | July 31, 2027 (Saturday) |
Start date: January 31, 2026. Other inputs kept at the calculator's default values. Results calculated by this calculator.
Why use a Month Calculator?
Find billing dates, contract ends and anniversaries by month.
Important factors that can affect your results
- Month-end rule (Jan 31 + 1 month = Feb 28/29).
- Some contracts use 30-day months instead.
- Leap years.
Frequently asked questions
What happens with January 31st plus one month?
It correctly returns February 28th (or 29th in a leap year) — since February 31st doesn't exist.
Can I calculate months in the past?
Yes — enter a negative number of months to go backward.
Related calculators
Last reviewed November 2026 · How we build and check our tools · Report a problem