Arrive in the UK partway through a tax year and, in most cases, you don't get taxed as a UK resident for the whole year. Split year treatment divides the year into an overseas part and a UK part — but which of HMRC's 8 cases applies, and how the split interacts with an OWR or FIG regime claim, is where the SA109 notes get genuinely easy to misread.
The 8 cases, and which ones are about arriving
HMRC's SA109 notes list eight sets of circumstances for split year treatment. Two are specifically about starting to have a UK home:
- Case 4 — starting to have a home in the UK only ("not meet the only home test at the start of the tax year, but at some point in that tax year they do... and continue to do so until the end of that tax year" — RFIG21150).
- Case 8 — starting to have a home in the UK, the residual case for people who don't cleanly meet Case 4's "only home" test but who otherwise start having a UK home and continue to for the rest of that year and all of the next (RFIG21270).
Case 5 (starting full-time work in the UK) can also apply if employment is what's actually driving the move, and Case 1/2/3/6/7 cover the opposite direction — leaving or ceasing overseas work — so they generally won't apply to an arrival. Both Case 4 and Case 8 require you to not already have sufficient UK ties for the period before you start having a UK home; each case has its own reduced day-count thresholds for that pre-arrival window, set out in HMRC's manual rather than a fixed number that applies to everyone.
If more than one case could plausibly apply to your facts, HMRC's notes require you to say which one(s) in the "any other information" box of your return, not just tick split year and move on.
What the split actually changes on your return
Per the SA109 notes, ticking box 3 (split year treatment applies) changes several other boxes:
- You do not tick box 1 (non-UK resident) — split year treatment is only available if you're UK resident for the year overall.
- Box 6 needs the date the UK part of the year begins.
- Box 10 (UK day count) is only for the overseas part of the year — not your full-year day count, which is a common misread.
- Box 12 (UK ties) is only required if Case 4 or Case 8 applies, and only covers the overseas part of the year.
During the UK part of the split year, you're taxed as a full UK resident on worldwide income and gains. During the overseas part, generally only on UK-source income.
Where this meets OWR and the FIG regime
Split year treatment answers one question: how is this specific transitional tax year taxed. It doesn't, by itself, redefine your FIG regime qualifying window or your OWR workday sourcing period — those run off your actual residence-start date and the specific work/vesting periods involved, which will usually align with your split year date but should be checked against it rather than assumed identical, particularly if your UK-part start date and your first day of UK employment aren't the same day.
For RSUs specifically, this is the same principle as RSU sourcing running on its own clock: a tranche vesting in your arrival year can be sourced across a grant-to-vest window that spans your split year boundary, your pre-arrival period entirely, or both — the split year date on its own doesn't tell you where that window's overseas fraction falls.
Where FIG Tracker fits in
FIG Tracker tracks workdays from your actual arrival date forward, including any relevant pre-arrival period for tranches and bonuses whose sourcing window starts before you moved, and keeps that separate from the split year day-count HMRC wants in box 10. See qualifying new resident eligibility for how your 4-year FIG regime window is worked out alongside this.
FIG Tracker is a calculation aid, not tax advice. Always confirm which split year case applies to you, and your resulting eligibility, with a qualified tax advisor before filing with HMRC.