If you came to live in the UK during the 2025/26 tax year, or left it, for example to move back to Poland, and you need to send HMRC a Self Assessment return, there is a detail that catches many people out. Your return will usually need the SA109 residence pages, and HMRC's free online service cannot accept them.
That leaves two routes, with two different deadlines. A paper return must reach HMRC by 31 October 2026, which is just over two weeks away. Filing through commercial software or an agent keeps the usual deadline of 31 January 2027. Here is how to tell whether this applies to you and how to pick the right route.
In a nutshell
- Not everyone who moved must file. SA109 is for people who already need a return, or want a specific claim.
- HMRC online will not take SA109. You need paper, commercial software or an agent.
- Paper must arrive by 31 October. Software or an agent keeps 31 January.
- Missing 31 October is not the end. Switch to the online route, do not post late.
- Split year and FIG are claimed here. Both are reported on the SA109 pages.
- Some leavers only need a P85. If you do not normally file Self Assessment.
1. Who needs the SA109 pages
Moving to or from the UK does not, on its own, mean you must file a tax return. SA109 is a set of supplementary pages that go with the main return, the SA100. You need them if you already have to file Self Assessment, for example because you are self-employed, a landlord or a company director, or if you want to make one of the claims below.
HMRC's 2025/26 notes say to fill in the pages if you:
- were not resident in the UK for the 2025/26 tax year, or
- were resident and became UK resident during the year, are due split year treatment, or want to claim relief under the new foreign income and gains (FIG) regime.
The pages also cover a few less common claims, such as Overseas Workday Relief and Business Investment Relief. If you stayed UK resident all year and none of this applies, you do not need SA109.
2. Why HMRC online will not take your return
HMRC's free online Self Assessment service does not support the SA109 pages. Gov.uk says plainly that you cannot use HMRC's online services to report your income if you are non-resident, and that leavers cannot use them to tell HMRC they have left.
The SA109 notes add that if you want to submit these pages online, you need commercial software or a professional agent to file the return for you. They also say not to send the pages as an attachment to a return filed online. This is not new, but it still catches people out.
3. Your two routes and their deadlines
You have two ways to file the 2025/26 return with SA109:
- Paper route. Fill in the paper SA100 and SA109 and post them. They must reach HMRC by 11:59pm on 31 October 2026. If you are posting from abroad, allow plenty of time, because what counts is when HMRC receives the return, not when you post it.
- Online route through software or an agent. Use commercial software that supports SA109, or authorise an agent to file for you. The deadline is 31 January 2027. Gov.uk publishes a list of commercial software suppliers that shows which supplementary pages each product supports.
Whichever route you choose, the tax is still due by 31 January 2027. Filing on paper does not bring the payment date forward. Choose one route and stick to it: do not post a paper return and then file the same return online as well.
One exception is worth knowing. If HMRC sent you a notice to file a 2025/26 return after 31 July 2026, your deadline is later, generally three months from the date of that notice.
4. If you miss 31 October
Missing the paper date is not the end. HMRC's own guidance says people who cannot meet 31 October still have until 31 January to file online. In practice that means using software or an agent.
What you should not do is post a paper return in November. A paper return received after 31 October gets a £100 late filing penalty, even though the online route would still have been on time. Further penalties follow if a return is more than three months late.
Penalties can be appealed with a reasonable excuse, but HMRC's manual is clear that simply pointing to the lack of free HMRC software is not a reasonable excuse. Plan for the deadline of the route you actually use.
5. Split year treatment and the new FIG regime
Split year treatment applies when you move in or out of the UK during a tax year and your circumstances fit one of 8 cases set out by HMRC, such as starting full-time work overseas or ceasing to have a home in the UK. It is not an election. If a case applies, the year is split into a UK part and an overseas part, and you pay UK tax only on income arising in the UK part. You report it on SA109, giving the date and the case.
The 4-year FIG regime is new from 2025/26. It is open to people in their first four years of UK tax residence after at least 10 consecutive tax years of non-UK residence, whatever their nationality. It gives relief on foreign income and gains, at a cost: you lose your Income Tax personal allowance and your Capital Gains Tax annual exempt amount for that year. Most people who have lived in the UK before will not meet the 10-year condition. The claim for 2025/26 can be made up to 31 January 2028, so it can be added later by amending the return if needed.
6. Leavers who do not file a return
If you left the UK during 2025/26, were employed through PAYE and do not normally file Self Assessment, you usually do not need SA109 at all. Instead, you tell HMRC you have left using form P85, which can also be used to claim back tax you may have overpaid. It can be done online or by post.
You do not need a P85 if you are filing a Self Assessment return for the year you left, because the SA109 pages do that job.
A worked example: Tomasz returns to Poland
Tomasz is a self-employed plasterer working under the Construction Industry Scheme (CIS). From April to August 2025 he earned £14,000 for his labour, and his contractor deducted 20%, so £2,800 went to HMRC. In September 2025 he gave up his flat in Birmingham and moved back to Wrocław for good.
As a self-employed worker he must file a 2025/26 return, which is also how he reclaims any CIS tax overdeducted. Because he left during the year, he needs the SA109 pages, and depending on his facts he is likely to be due split year treatment.
When he tries to file through his HMRC online account, it will not take SA109. He has two choices:
- Post a paper SA100 and SA109 so they reach HMRC by 31 October 2026. Posting from Poland, he should send them this week, using tracked post.
- Ask an accountant to file online by 31 January 2027 using software that supports SA109.
If he posts the paper return on 5 November, he gets a £100 penalty. If he lets an agent file in December instead, there is no penalty, and any repayment of the £2,800 is worked out in the same way.
Things to watch out for
- Moving alone does not create a filing duty. Check whether you need a return before you start.
- The 31 October date is for paper only. Software and agents keep 31 January.
- Received, not posted. Paper returns must reach HMRC by 31 October.
- No free software is not an excuse. It will not get a late paper penalty cancelled.
- Payment is due on 31 January either way. The route does not change it.
- FIG is not free money. Claiming it costs you your personal allowance for that year.
How Ollen Services Can Help
Residence and split year treatment depend on the details: your dates, homes, work and income in both countries. Getting them wrong can mean paying UK tax you do not owe, or missing a refund.
As your agent, we can prepare your return with the SA109 pages and file it online, so you are not tied to the 31 October paper date. We can work out whether split year treatment applies, handle CIS refunds for subcontractors who have left the UK, and deal with HMRC on your behalf. We work in English and Polish.
Call us on 07513 491 259 or email hello@ollenservices.co.uk. If you are unsure which route you need, ask us now, while both deadlines are still open.