About the 180 Day Calculator
This tool finds the calendar date that sits exactly 180 days before or after a date you choose, then reports the day of the week, how that date compares to today, and the equivalent span in weeks and days. It is plain calendar arithmetic, done the way any date calculator does it — by stepping through the actual Gregorian calendar, not by dividing 180 by 30 and calling it "six months."
The formula
Given a start date S and a direction, the target date T is:
- 180 days after: T = S + 180 calendar days
- 180 days before: T = S − 180 calendar days
The start date itself counts as day zero, so adding 180 days lands exactly 180 calendar days later — the same convention used by spreadsheet date functions. Because the calculation walks through the real calendar (JavaScript's native date object), it automatically lands on the correct day even when the span crosses February in a leap year, a run of 30- and 31-day months, or a year boundary, with no manual adjustment needed.
Common uses
- Passport and travel planning: many countries require a passport to remain valid for six months (roughly 180 days) beyond the date of entry
- Visa and stay-limit tracking, such as counting days within a rolling 90-in-180-day window
- Legal and administrative deadlines that use a 180-day window, including some notice periods, filing deadlines, and dispute windows
- Business, warranty, and return-policy periods, plus half-year milestones and countdown planning
Precision note
Results use calendar days (every day counted equally), not business days — weekends and holidays are not skipped. If your 180-day window has legal, contractual, or immigration significance, confirm the exact counting rule that applies (some rules count the start date, some don't, and business-day rules skip weekends and holidays), since these conventions can shift the result by a day or more.