Add / Subtract Days Calculator

From the editors — what to know before you start

Add or subtract days, weeks, months, or years from any starting date — every adult needs this calculation regularly and most do it badly in their head. Common scenarios: 'when does my 3-month notice period end if I resigned on the 12th?', 'what's the Net-30 deadline on this invoice?', 'when does the 1-year warranty on this fridge expire?', '90 days before the wedding so I know when to start the diet'. The tricky bit is that 'one month' is genuinely ambiguous. Is it 30 days exactly, or the same date next month? The calculator uses calendar-month arithmetic — January 31 plus one month gives February 28 (or 29 in a leap year), not March 3 — which matches what humans actually mean when they say 'one month later'. Leap years are handled correctly: February 29 plus one year in a non-leap year cleanly becomes February 28, not a bogus invalid date. Weeks are simple groups of 7 days; the 4-week-is-not-a-month confusion trips up everyone at least once. Pakistani-specific landmines: Net-30 invoice terms are by calendar days not working days, so a Friday invoice is due the Sunday four weeks later (and most clients pay the following business day without it being late). Court filings, FBR deadlines, NADRA appointment scheduling — most use calendar days, but check the specific document. Pro tip: for pregnancy due date (LMP plus 280 days), warranty tracking, and any contractual deadline, save the calculated date in your phone calendar immediately. Mental notes about 'oh that's roughly mid-July' is how people miss penalty deadlines.