Date Add & Subtract Calculator
Add or subtract days, weeks, months or years from a date.
How it works
Adding months is the awkward case. 31 January plus one month has no obvious answer, because 31 February does not exist. The convention used here — and by most software — is to clamp to the last valid day, giving 28 or 29 February.
That makes month addition non-reversible: add a month to 31 January and subtract it again and you land on 28 February, not where you started.