What is 31 January plus one month?

The last day of February. When the target month has fewer days, the result is clamped to its final day.

Is anything I enter stored?

No. Dates are processed in your browser and are not sent or saved.

JavaScript is turned off. InspireTools processes files in your browser, so the tools need JavaScript to run.

Add or subtract years, months, weeks and days from a date.