Add or subtract any number of days, weeks, months or years from a start date.
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How This Works
Days/weeks: add or subtract directly from the date. Months: add to the month component (JavaScript handles month overflow automatically — e.g. Jan 31 + 1 month = Feb 28/29). Years: add to the year component. Leap year edge case: adding 1 year to Feb 29 gives Feb 28 in a non-leap year.
When you add one month to January 31st, you get February 31st — which does not exist. JavaScript (and most date libraries) handles this by rolling over to the next valid date: March 2nd or 3rd. Similarly, adding 1 month to October 31st gives November 30th (not 31st). If you need exact "same day next month" logic for billing or contracts, always verify the result date.