Double Tax Relief: How to Avoid Being Taxed Twice on the Same Income

Double taxation happens when two countries both tax the same income or gain, and the UK relieves it either by treaty or, where no treaty applies, by unilateral relief under its own law. The clash usually arises because one country taxes on the basis of source (where the income arises) and the other on the basis of residence (where the person lives). A UK resident with rent from a French flat, a US pension or interest from an overseas bank can find both the UK and the other country want tax on the same money.

Where a double taxation treaty exists with the other country, the treaty decides which country has the taxing right and how relief is given. Where there is no treaty, or the treaty does not cover the particular income or tax, the UK gives unilateral relief under its own domestic law (the Taxation (International and Other Provisions) Act 2010, or TIOPA 2010). Both routes deliver relief mainly as a credit for foreign tax against the UK tax on the same income or gain.

Relief reduces double tax; it does not refund foreign tax to a level below what the UK would have charged. The aim is that you pay the higher of the two countries' tax overall on that item, not both in full.

Foreign Tax Credit Relief gives you a credit against your UK tax for foreign tax suffered on the same income or gain, and it is capped at the UK tax due on that item. The credit is the lower of two figures: the foreign tax actually paid or allowed under the treaty, and the UK tax due on that same income. That second figure is the cap, and it is the reason FTCR can never wipe out more than the UK tax on the income.

The cap bites hardest when the foreign country's tax rate is higher than the UK's. If you paid more foreign tax than the UK charges on the item, the excess foreign tax is not available for credit against your UK liability and HMRC will not repay it. Your only route for that excess is to claim it back from the foreign tax authority, often by using their treaty rate or a refund procedure.

Treaty relief is the first port of call, and unilateral relief is the fallback that fills any gap. The UK has one of the largest treaty networks in the world, with more than 100 agreements largely following the OECD Model. A treaty allocates taxing rights between the two countries, often reduces or removes foreign withholding tax at source, and sets the residence tie-breaker that decides who is treated as resident where.

Where no treaty applies, or a treaty exists but does not cover the specific income or tax, the UK still gives credit for foreign tax under TIOPA 2010. It is a genuine safety net, but not a more generous one: unilateral relief is limited to the amount that would have been due if a treaty had been in existence. So whether relief comes by treaty or unilaterally, the credit is broadly the same.

• Treaty relief: available where a double taxation agreement covers the income; can also reduce foreign withholding at source.
• Unilateral relief: applies where there is no treaty, or the treaty is silent on that income or tax.
• Both give credit for foreign tax, capped at the UK tax on the same item.
• Unilateral relief is capped to the treaty-equivalent amount, so the choice of route rarely changes the figure.

If both the UK and another treaty country treat you as resident under their own rules, the treaty's tie-breaker decides which country wins for treaty purposes, applying its tests in a fixed order and stopping at the first one that gives a clear answer. The same person can still be UK-resident under the Statutory Residence Test domestically while being treaty-resident elsewhere; the tie-breaker simply governs how the treaty allocates taxing rights.

Most cases are resolved at step one or step two. Nationality only comes into play in the narrow situation where habitual abode does not separate the two countries, and mutual agreement is the last resort. The tie-breaker outcome drives your entitlement to UK treaty relief, so it is worth getting the analysis right rather than guessing.

This illustrative example shows the cap in action. Priya is UK-resident in 2026/27 and is a higher-rate taxpayer (her other income already uses her GBP 12,570 Personal Allowance and pushes this source into the 40% band). She receives GBP 10,000 of gross foreign rental profit and pays GBP 3,000 of foreign tax on it.

• UK tax on the GBP 10,000 at 40% = GBP 4,000.
• Foreign tax paid = GBP 3,000.
• FTCR = the lower of GBP 3,000 (foreign tax) and GBP 4,000 (UK tax) = GBP 3,000.
• UK tax still payable after credit = GBP 4,000 less GBP 3,000 = GBP 1,000.
• Total tax across both countries = GBP 3,000 plus GBP 1,000 = GBP 4,000, the same as the UK figure alone.

Now flip the numbers. If the foreign tax had been GBP 5,000, FTCR would be the lower of GBP 5,000 and GBP 4,000, so the credit is capped at GBP 4,000. UK tax falls to nil, but the extra GBP 1,000 of foreign tax above the cap is not repayable by HMRC. Priya would need to look at recovering that GBP 1,000 from the foreign authority, for example by claiming the treaty rate there.

Taking foreign tax as a credit is the default, but you can instead elect to deduct it from the foreign income. Under the deduction route you are taxed on the net amount rather than taking a credit on the gross. This is an election: you pick whichever is more favourable.

Deduction is usually worse than a credit, because a credit reduces tax pound for pound while a deduction only reduces the taxable amount. It tends to help only in narrow situations, for example where the UK tax on the item is nil or very low, or where you have losses that would otherwise waste the credit. Treat deduction as the exception, not the starting point, and model both before deciding.

If you are UK-resident and claiming relief for foreign tax on your worldwide income, you claim through Self Assessment on the SA106 foreign pages, filed with your SA100 tax return. This is the route for FTCR and for reporting foreign income and the foreign tax suffered on it. The supporting helpsheet HS263 sets out the per-source calculation.

Form DT-Individual does a different and specific job: it is for a resident of a treaty country who wants relief from UK Income Tax under that treaty, both at source and as a repayment of UK tax already deducted. Its scope is UK-source pensions, purchased annuities, interest and royalties. It is not a general UK-resident form for relieving foreign tax, so do not reach for it if you live in the UK and are dealing with foreign income; use SA106 for that.

The 6 April 2025 reforms changed who is taxed on foreign income, but they did not change how double tax relief itself works. The abolition of the remittance basis and the new Foreign Income and Gains (FIG) regime reshaped the charge, while the credit mechanism, the cap and the tie-breaker are long-standing and remain in place for 2026/27.

The practical link is this: if your foreign income is within scope of UK tax (for example because you are outside the four-year FIG window, or the income is not FIG-eligible), then double tax relief is how you avoid being taxed twice on it. If new arrivals are using FIG relief so that the foreign income is not UK-taxed at all, there is no UK tax for a credit to reduce. Our FIG regime guide covers who qualifies.

This guide is the foundation, and the next step depends on which income you hold. The detail of how relief applies varies by income type, because each has its own treaty article, withholding rules and reporting quirks. From here, move to the guide that matches your situation.

• Foreign rental income: how overseas property is taxed in the UK and how to credit foreign property tax.
• Foreign pensions and QROPS: treaty treatment of overseas pensions, lump sums and transfers.
• US-UK tax: the particular complications of the saving clause, US citizenship-based taxation and resourcing.
• Expat Self Assessment: how the foreign pages and residence pages fit together on your return.

If you would like the calculations done and the right forms filed correctly the first time, we work on fixed fees agreed upfront and can take the whole claim, the SA106 figures and the credit-versus-deduction test off your hands. Book a call and we will tell you exactly what your relief is worth before you commit.