How many months is 183 days?
Short answer: 183 days is just over six months — six months plus one day in a 365-day year, or about 26 weeks and one day. It is the smallest whole number of days that is more than half a year, which is exactly why so many countries use it as the tax-residency threshold: spend 183 days there and you were present for the majority of the year.
The arithmetic
- In months: six months and one day in a normal year (365 ÷ 2 = 182.5, so 183 is the first whole day past halfway). In a leap year 183 days is exactly half of 366.
- In weeks: 26 weeks and 1 day (26 × 7 = 182).
- As a share of the year: 50.1% — a bare majority.
- On a calendar: 1 January to 2 July inclusive is 183 days in a non-leap year; 1 January to 1 July in a leap year.
Why 183 and not 180 or six months
Tax law needs a bright line for “more than half the year.” “Six months” is ambiguous — months are 28 to 31 days long — and 180 days is slightly less than half a year. 183 is the smallest count that is unambiguously a majority of any year, leap or not, so it became the standard threshold in domestic residency rules and in tax treaties (the OECD model uses 183 days to decide which country may tax a short-term worker’s salary). That is the whole story behind the 183-day rule.
The near-miss numbers you will also see are deliberate: the Schengen area’s tourist limit is 90 days in any 180 (half of a half-year), and the UK’s ILR rule allows 180 days of absence in any 12 months. Those are immigration limits, not tax tests, and they are set just under the halfway mark on purpose.
Counting 183 days correctly
The months-to-days conversion is the easy part. What trips people up is which days count and over which period:
- Part days. Many countries (the US, Spain, Canada) count any day you are physically present, so arrival and departure days both count. The UK counts a day only if you are there at midnight.
- The window. A calendar year, the country’s own tax year (UK: 6 April–5 April; Australia: 1 July–30 June), or any rolling 12-month period (Brazil, Chile, Colombia). A rolling window means 183 days across two calendar years can still trigger residency.
- Weighted counts. The US Substantial Presence Test reaches 183 by adding this year’s days to one-third of last year’s and one-sixth of the year before — so you can “hit 183” with only 122 days in the current year.
The free 183-day calculator counts from your actual trip dates across a calendar year, tax year, or rolling window, so you never have to convert months to days by hand.
Related questions
Sources
For information only. This page is a plain-English summary of publicly available rules, not tax, legal, or immigration advice. Rules change and depend on your personal circumstances — always confirm with the official source above and a qualified professional before acting.