Contracts, notice periods, warranties, filings, and personal goals are often written in days instead of months. "180 days" sounds like six months, but the two are not the same, and being off by a day or two can matter on a deadline.
180 days is not exactly six months
Months vary from 28 to 31 days, so six months is between 181 and 184 days long depending on where you start. A fixed 180 days is shorter. In weeks, 180 days is 25 weeks and 5 days (180 ÷ 7 = 25.71).
How to count it by hand
- Start with your start date and decide whether the start day counts. Most deadline rules count the day after the start as day 1, but always check the wording of your document.
- Add days month by month, using the actual length of each month.
- Land on the resulting date and note its weekday; if the deadline falls on a weekend or holiday, your rules may move it.
A worked example
Start on January 1 in a non-leap year. January has 31 days, February 28, March 31, April 30, and May 31, which totals 151 days and takes you to June 1. Add the remaining 29 days and you land on June 30. In a leap year, February has 29 days, so the same count lands on June 29.
Common mistakes
- Counting the start day when the rule says to start the next day, or the reverse.
- Using months instead of days, which shifts the date by up to four days.
- Mixing calendar days and business days. Business-day counts skip weekends and holidays and land much later.
- Forgetting leap years when the range crosses February 29.
- Confusing 180 with 183. Some residency tests use 183 days, a different threshold with its own rules.
This is general information, not legal advice. For a real deadline, confirm the counting rule in your document or with the issuing office.
Skip the counting
The 180 Day Calculator gives the exact date 180 days before or after any start date, including the weekday.