Add or Subtract Days

Adding days is the simplest case: shift the calendar forward by N. February 28 + 1 day = March 1 (or February 29 in a leap year). The browser's Date object handles month and year rollovers automatically — no need to special-case month lengths.

Adding months is trickier because months have different lengths. The convention this tool uses (and that JavaScript's Date object uses) is: January 31 + 1 month = March 3 (because Feb only has 28 days, so day 31 overflows). If you need 'last day of next month' semantics, use a dedicated end-of-month function.

Adding years works cleanly except on leap day. February 29, 2024 + 1 year = March 1, 2025 in this tool — the day rolls over because 2025-02-29 doesn't exist. For birthdays of leap-day babies, most jurisdictions treat Feb 28 (non-leap years) as their celebration date.

Business days skip Saturdays and Sundays. This tool does not skip statutory holidays — for legal contract dates that exclude federal holidays, use a country-specific holiday list. For most planning purposes (Mon–Fri sprints, ship dates), the simple Mon–Fri filter is what you want.

Project deadline: today is Friday Mar 14, 2025. Add 30 days → Sunday Apr 13, 2025. Add 30 business days → Friday Apr 25, 2025 — the business-day version is six calendar weeks because of weekends.

Contract notice: notice given Jan 15, 2025, terminates after 90 days. 90 days from Jan 15 = April 15. 90 business days = May 21 — for legal notice periods, always check whether the contract specifies calendar or business days.

Project planning: kickoff Sept 2, 2025. Beta in 8 weeks: Oct 28. GA in 6 months: March 2, 2026. Use months for long-horizon roadmap dates and weeks for sprint cadence.

Subtract example: invoice due Mar 31; subtract 14 days for early-payment discount cutoff: Mar 17.

Project & sprint planning: 'sprint ends in 14 days', 'kickoff + 90 days = release window'.

Legal & contracts: notice periods (30/60/90 days), statute-of-limitations clocks, lease auto-renewal cutoffs.

Healthcare: gestational age (weeks since LMP), follow-up appointment intervals, prescription refill timing.

Education: assignment due dates, exam countdowns, semester week numbers.

Finance: payment terms (net-30, net-60), credit-card grace periods, 1099 quarterly payment dates.

Personal: visa expiration, passport renewal lead time, 'how many days until vacation'.

Calendar vs. business days for legal deadlines — courts often count calendar days but exclude the day of filing and any final-day weekend/holiday. Always check the specific rule before relying on a generic count.

Time zones: this tool treats every date as a calendar date with no time component. If you need a precise 'add 72 hours' across time zones, use a datetime tool instead.

Leap days: adding 1 year to Feb 29 lands on Mar 1 in non-leap years. Build any logic that anniversaries Feb 29 with explicit handling.

DST shifts: not relevant for date-only math (this tool ignores hours), but adding '24 hours' to a datetime can land you in the wrong calendar day on DST changeover weekends.