As thousands of professionals prepare to leave the United Kingdom in 2026 for work, retirement, or relocation, a surprising number overlook one crucial part of the process — their UK tax obligations. For many, the excitement of moving abroad overshadows the fine print of HMRC compliance, resulting in unexpected bills, penalties, and, in some cases, double taxation.
Every year, British expats collectively lose millions of pounds in unnecessary tax payments simply because they fail to submit the right forms before leaving. In some instances, a few missed pages can result in over £10,000 in losses — all due to errors that could have been avoided with proper advice and planning.
This comprehensive guide outlines the seven HMRC forms most commonly forgotten by UK expats and explains how to complete them correctly before departure to remain compliant, protect income, and avoid hefty fines.
1. Form P85 — The Starting Point for All Leavers
The first and most essential form for anyone leaving the UK is Form P85, officially titled Leaving the UK – getting your tax right. It is the declaration HMRC requires to determine whether an individual remains a UK taxpayer or becomes non-resident for tax purposes.
The P85 is designed for those who are:
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Moving abroad permanently or for full-time work, or
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Leaving the UK for at least one full tax year.
Why it matters
Failure to submit a P85 means HMRC continues to treat the individual as a UK resident, potentially taxing worldwide income even after they have relocated. This oversight often leads to double taxation — once in the UK and again in the new country of residence.
Common mistake
Many departing residents assume their employer’s payroll submission or P45 automatically informs HMRC of their departure. In reality, the P45 only reports that employment has ended, not that the person has left the UK. The P85 must still be filed directly with HMRC, ideally before or immediately after departure.
2. Form SA109 — The Statutory Residency Test in Practice
The SA109 form, an attachment to the Self Assessment tax return, is vital for anyone who continues to have UK income after leaving — such as rental earnings, dividends, or pensions.
Why it matters
The SA109 determines residency status under the Statutory Residence Test (SRT). It helps HMRC understand whether the individual should be taxed on worldwide income or only UK-sourced income.
Common mistake
Many expats incorrectly assume that once they have left the country, they automatically become non-resident. However, UK tax residency is determined by specific rules: the number of days spent in the UK, family connections, and ties such as a UK home or employment.
The cost of omission
Failure to file SA109 can result in HMRC treating the taxpayer as resident for the full year — a costly error that can lead to demands for unpaid tax on foreign earnings.
3. Form R105 — For Non-Residents Earning UK Interest
Expats who continue to hold UK savings accounts, ISAs, or investments often overlook Form R105, which allows them to receive interest “gross” — that is, without automatic tax deduction at source.
Why it matters
Without an R105, banks and building societies will automatically deduct basic rate tax (20%) from savings interest, even if the individual is now a non-resident and no longer liable for UK tax on such income.
Example
A retiree relocating to Spain with £100,000 in UK savings could lose up to £1,000 each year to unnecessary deductions simply for failing to complete a one-page form. Over a decade, that’s £10,000 lost needlessly.
4. Form DT-Individual — Claiming Double Tax Relief
The DT-Individual form is crucial for anyone moving to a country that has a double taxation agreement (DTA) with the UK. These agreements prevent the same income from being taxed twice — once in the UK and once in the new country of residence.
Why it matters
By submitting DT-Individual, expats can claim relief at source or receive a refund for tax already deducted in the UK.
Common mistake
Many taxpayers assume the DTA works automatically. In reality, the relief must be formally claimed via the correct form and certified by the foreign tax authority — a process that can take months if not initiated early.
Financial impact
Failing to file DT-Individual can result in overpayment of thousands in taxes, particularly on pensions, dividends, or interest income.
5. Form SA106 — For Income From Abroad (During Transition Year)
The SA106 is the foreign income supplement to the Self Assessment return. It applies to individuals who earn income abroad while still technically UK resident, such as during a transition year of partial residence.
Why it matters
Many professionals working overseas during the first year of relocation mistakenly assume their foreign salary is exempt from UK tax. Unless non-residency is formally established under the Statutory Residence Test, such income must still be declared on SA106.
The risk
HMRC penalties for undeclared foreign income can be severe — up to 200% of the unpaid tax, plus interest. For high earners, this can easily exceed £10,000.
6. Form CF83 — Continuing National Insurance Contributions Abroad
One of the most commonly overlooked forms, CF83, allows expats to voluntarily continue paying UK National Insurance (NI) contributions while living abroad.
Why it matters
Maintaining voluntary Class 2 or Class 3 NI contributions can protect eligibility for:
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The UK State Pension
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Certain benefits linked to contribution years
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Healthcare entitlements in the UK upon return
Example
An individual who stops paying NI for 10 years abroad could lose entitlement to several thousand pounds in annual pension income later in life. Completing CF83 prevents this gap and ensures long-term financial security.
7. Form R43 — Claiming Tax Refunds for Non-Residents
Finally, Form R43 is used to claim back UK tax deducted from income after becoming non-resident — such as from savings, pensions, or trust distributions.
Why it matters
If tax continues to be deducted automatically, non-residents can claim refunds for up to four previous tax years. Many expats remain unaware of this entitlement, leaving significant sums unclaimed.
Typical scenario
A professional moving to Dubai in 2026 continues receiving taxed interest from a UK bank for three years. Upon learning about R43, they reclaim nearly £3,200 in overpaid tax.
The True Cost of Forgetting
Each of these forms may seem minor in isolation, but together they represent a significant financial safeguard. Missing even one can result in:
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Unnecessary UK taxation on foreign income
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Missed refunds and reliefs
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Delays in non-residency recognition
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Loss of pension or NI benefits
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Double taxation and compliance penalties
When compounded, these oversights can exceed £10,000 in financial impact, not counting the time and stress of resolving disputes with HMRC after leaving the UK.
The Administrative Challenge
Completing the necessary forms requires not only accuracy but also sequencing. For instance, a P85 should generally be filed before SA109, while DT-Individual relief claims often depend on residency confirmation. Errors in timing or cross-referencing can trigger HMRC investigations or delayed refunds.
Many expatriates underestimate this complexity, assuming the forms are straightforward. In reality, understanding how one declaration interacts with another — and how each impacts residency status — requires professional expertise.
How to Prepare Before Leaving
To stay compliant and stress-free, experts recommend the following steps at least three months before departure:
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Gather documentation: bank details, PAYE records, P45/P60 forms, proof of foreign employment, and address abroad.
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Complete the P85 and notify HMRC of departure date.
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Determine residency status using the Statutory Residence Test.
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Check for outstanding tax liabilities from the current year.
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Review ongoing UK income sources such as property, savings, or pensions.
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Claim reliefs and refunds proactively via R105, R43, or DT-Individual.
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Seek professional advice to ensure every form is correctly completed and filed on time.
Why Professional Guidance Matters
UK tax law for expatriates is notoriously intricate, especially when navigating overlapping tax years, foreign income sources, and double taxation agreements. A professional tax accountant can ensure every declaration aligns with the correct residency classification, preventing unnecessary exposure to UK tax.
Engaging a trusted firm such as My Tax Accountant allows individuals to handle the process efficiently and accurately. Their team specialises in expat tax management, ensuring all seven forms — and their related reliefs — are correctly addressed before departure.
From completing the initial P85 to claiming refunds under R43, professional oversight can save both money and frustration, giving departing residents peace of mind that they have closed their UK tax affairs properly.
Final Thoughts: Leaving Smart, Not Sorry
Relocating abroad marks an exciting new chapter, but without proper tax planning, it can quickly turn into a costly administrative ordeal. HMRC compliance is not optional — and neither is awareness of the paperwork required.
By taking time to complete these seven forms before departure, every UK expat can safeguard income, secure future benefits, and avoid thousands in unnecessary tax charges.
In 2026, those who leave prepared will enjoy a seamless transition to their new life abroad. Those who don’t may find that HMRC follows them across borders — with penalties attached.
The moral is simple:
Leaving the UK doesn’t mean leaving tax obligations behind. Understanding and acting on them — before the plane takes off — can make the difference between a £10,000 loss and a lifetime of financial peace.
