Add Months to a Date Calculator
Add or subtract months from a date, clamping month-end correctly.
What is Add Months?
“Add one month” is ambiguous on the 29th, 30th or 31st, and naïve date arithmetic gets it wrong by rolling into the next month: January 31 plus a month should be the end of February, not March 2 or 3. Contract end dates, billing anniversaries and subscription renewals all land on this edge, so the clamping rule matters.
How it works
The target month is found first, then the day is set to the smaller of the original day and that month's length — 31 clamps to 28 in February, 29 in a leap year. When clamping happens the tool says so, naming the original and applied day, so a contract date is never silently a day off.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Paste or type any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.