Add or Subtract Days from a Date

Finding a date a set number of days away

Many everyday deadlines are defined as a number of days, weeks or months from a starting date. A product return window of 30 days, a 90-day free trial, a notice period of two months, a medicine course of 21 days or a payment due 45 days after an invoice are all easier to manage when you know the exact calendar date. This calculator finds it in a moment, forwards or backwards.

Adding months needs a little care, and the calculator follows the usual convention. One month after 31 January cannot be 31 February, so the result moves to the last day of February instead. Adding days is always exact, which is why many contracts specify periods in days rather than months. If a rule says '30 days', add days; if it says 'one month', add a month, because the two can give different dates.

Subtracting is just as useful. If a visa application must be submitted at least 45 days before travel, enter the travel date and subtract 45 days to find your latest safe date. Event planners often work backwards like this from the event day to set milestones for invitations, bookings and payments. Once you have the date, add it to your phone calendar with a reminder a few days earlier, so the deadline does not slip past unnoticed. For legal or official deadlines, check whether weekends and public holidays are counted, since some authorities extend a deadline that falls on a holiday to the next working day, while others do not.