Strictly, you are UK tax resident for the whole of a tax year when you are UK resident for any part of it. But, if you leave or come to the UK partway through a tax year, HMRC operates a concession under which the year may be split (Extra-Statutory Concession A11).
This has the effect of splitting the tax year into resident and not resident periods for the purposes of calculating the tax due. The split year concession may be available for those who:
- Come to the UK to take up permanent residence or to stay for at least two years, OR
- Leave the UK to become permanently resident abroad, OR
- Leave the UK for fulltime service under a contract of employment for at least a complete UK tax year and any interim visits to the UK in the period do not amount to 183 days or more in any tax year or an average of 91 days or more in a tax year.
There is a related ExtraStatutory Concession (A78) which can allows split year treatment for those accompanying their spouse or civil partner when they leave the UK to work fulltime abroad, or in the year of return to the UK.
These concessions are for income. The rules for capital gains differ from those for income.
ExtraStatutory Concession D2 is a split-year concession which dealing with the capital gains of people who come to, or leave, the UK during a tax year