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Move to a new country in March or September and one question follows you into the next filing season: which of your days count as resident, and which don't?
The year rarely splits itself neatly
Residency is usually decided across a whole tax period, but relocations happen on an ordinary Tuesday in the middle of one. Most people who move across a border do it partway through a tax year, and the systems on both sides then have to decide how to treat the two halves. There is no single answer. Some countries carve the year in two, some apportion it, some tax the resident stretch on your worldwide income — and which rule applies, and from which day, depends on the country.
The tax years don't even line up. The UK runs 6 April to 5 April; Ireland and the United States use the calendar year; Australia runs 1 July to 30 June. So "mid-year" means four different things before you start. What follows are four official approaches to the same event — arriving or leaving partway through — and the one thing they all have in common.
| Country | Tax year | A mid-year move is treated as… |
|---|---|---|
| United Kingdom | 6 Apr – 5 Apr | Split-year: the year divides into a UK part and an overseas part (if you qualify) |
| Ireland | Calendar year | Split-year, but for employment income only, from your move date |
| United States | Calendar year | A "dual-status" year: resident for part, nonresident for the rest |
| Australia | 1 Jul – 30 Jun | No split; a reduced, pro-rated tax-free threshold for the months you were resident |
Britain: a statutory split, but only sometimes
The UK has formal split-year treatment written into the Statutory Residence Test. It only bites once you are already UK resident for the whole tax year under the test — as HMRC's RDR3 guidance puts it, "you'll be resident in the UK for the whole of a tax year, but that year may be split into a UK and an overseas part." The UK part is taxed as resident; the overseas part broadly is not.
There are eight cases — Cases 1 to 3 for people leaving the UK, Cases 4 to 8 for people arriving — and each has its own conditions that must all be met. When more than one case applies, priority rules pick a single case and, with it, the one date the year splits on. The nuance worth holding onto: split-year treatment doesn't change whether you are resident — that is still decided by the Statutory Residence Test and its day counts — only how the year is taxed once you are.
Ireland: a split for your salary
Ireland offers split-year treatment too, but narrower. Per Revenue, "split-year treatment applies to employment income only." Arrive to take up residence and you are treated as resident from your date of arrival; the employment income you earned abroad before arriving "is ignored for Irish tax purposes" — provided you are also resident the following year. On the way out, the mirror applies: you must be resident in your year of departure and not resident the next, leaving for more than a temporary purpose, and foreign employment income earned after you go is left out.
Because the relief covers wages only, other income — rents, investments — can still fall inside the Irish net for the whole year, so it is not the clean cut it first looks like. For moves after 31 December 2024, Revenue lets you claim it by self-assessing on your income tax return.
America: a dual-status year
The United States doesn't call it a split, but the effect is similar. Become or stop being a US resident partway through the year and you may file a dual-status return. The IRS is blunt about the difference in treatment: for the part of the year you are a resident you are "taxed on income from all sources"; for the nonresident part, only on US-source income. Dual-status filers give up some benefits — no standard deduction, itemising instead — and residency itself is set by the green-card test or the Substantial Presence Test, which is, again, a day count.
Australia: no split, a smaller threshold
Australia takes a different route. There is no year-splitting; instead, a part-year resident gets a reduced tax-free threshold. The full threshold is A$18,200, but a part-year resident receives a fixed base plus an amount apportioned by the number of months they were resident. To work it out, the Australian Taxation Office asks for the exact date you became — or stopped being — a resident, and counts the months from there. The mechanism differs; the dependency on a date does not.
The one thing they share
Four systems, four mechanics — and one hinge. Whether the year is split, apportioned, or filed dual-status, the boundary is a single date you must be able to state and defend, sitting on top of the day count that made you resident in the first place. Move that date by a few weeks and the resident portion — and the tax that rides on it — moves with it. It is also exactly the window in which two countries can each claim you, which is where the treaty tie-breaker comes in.
All of this is genuinely country-specific and changes over time — the rules above are current examples, not universal ones — so confirm your own case against the official source or a qualified adviser.
Keep the date you can prove
The day you arrived or left isn't paperwork trivia; it is the pivot the whole year turns on. Reconstructing it a year later from memory and old boarding passes is precisely where errors and disputes begin. Countly keeps a quiet, automatic record of when you entered and left each country — on your phone, no account — so the date that splits your year, and the day counts behind your residency, are already there when the form asks.