UK Inheritance Tax rules changed significantly from 6 April 2025, including the way the UK decides whether someone living overseas remains within IHT on their worldwide estate.
Under the old system, domicile played a central role. The new rules focus much more directly on your history of UK tax residence.
For British expats living in Thailand, this creates an important practical question:
After you leave the UK, how long can your Thai and other overseas assets remain within UK Inheritance Tax?
If you became a long-term UK resident before leaving Britain, the answer can be between three and ten UK tax years.
This ongoing period is commonly referred to as the IHT tail. Its length depends on your UK residence history and the UK tax years involved, not simply the date you moved to Thailand.
For many long-established expats in Thailand, reaching the end of the tail can be particularly significant. Personally owned overseas assets may then fall outside UK IHT, while Thailand’s much narrower inheritance tax regime applies only in particular circumstances depending on the assets and who inherits them.
This article explains how the IHT tail works, how to estimate your own exit date and what can still remain within UK IHT afterwards.
How the IHT Tail Works
Becoming Thai tax resident does not, by itself, end UK Inheritance Tax on your overseas assets.
You can be:
- Tax resident in Thailand
- Non-UK resident for general UK tax purposes
- Still a long-term UK resident for UK Inheritance Tax
‘Long-term UK resident’ is the statutory IHT status used under the new rules. It does not simply mean someone who has lived in Britain for a long time.
Broadly, you become a long-term UK resident once you have been UK tax resident for at least 10 of the previous 20 tax years.
For tax years from 2013/14 onwards, UK residence is normally determined under the Statutory Residence Test. Earlier years may need to be considered under the residence rules that applied at the time.
Once you have built up long-term UK resident status, leaving Britain does not switch it off immediately.
Think of the IHT tail as a delayed switch-off. You may already be living permanently in Thailand while your Thai and other overseas assets remain within the UK IHT net for several more tax years.
How Long Is Your IHT Tail?
For someone leaving the UK, the tail is based on the number of UK-resident years in the 20 tax years ending with their last UK-resident tax year.
| UK-Resident Years in that 20-Year Period | Standard IHT Tail |
| 10 to 13 | 3 tax years |
| 14 | 4 tax years |
| 15 | 5 tax years |
| 16 | 6 tax years |
| 17 | 7 tax years |
| 18 | 8 tax years |
| 19 | 9 tax years |
| 20 | 10 tax years |
Ten years is the maximum IHT tail. Your own period depends on your UK residence history.
For example, someone with 11 relevant UK-resident years will normally have a three-year tail. Someone with 15 years will normally have five years. Someone who was UK resident throughout all 20 relevant years can have the full ten-year tail.
The required years of non-UK residence normally must be consecutive. If you become UK resident again before completing the tail, that run is broken and your position must be recalculated.
What you do in Thailand does not determine when the tail ends. Becoming Thai tax resident, obtaining a Thai tax number, buying Thai property or moving money overseas does not, by itself, remove your overseas assets from UK IHT.
The key factors are your previous UK residence history and how many consecutive non-UK-resident tax years you complete after leaving.
How to Calculate Your IHT Exit Date
The IHT tail is measured in UK tax years, not from the calendar date you move to Thailand.
The UK tax year runs from 6 April to 5 April. Importantly, if you qualify for split-year treatment in the year you leave, that tax year still counts as a full UK-resident year for this IHT test.
Your first non-UK-resident tax year for the tail may therefore begin in the following tax year. This is why simply adding three, five or ten years to your moving date can give you the wrong exit date.
Example: James Moves to Thailand after a Lifetime in the UK
James has lived and worked in the UK throughout his adult life. He moves permanently to Thailand during the 2026/27 tax year and qualifies for split-year treatment.
For IHT purposes, 2026/27 still counts as a UK-resident year. His first non-UK-resident tax year is therefore 2027/28.
James has 20 relevant UK-resident years, so the maximum ten-year tail applies:
2026/27: Final UK-resident tax year
2027/28 to 2036/37: Ten consecutive non-UK-resident tax years
From 6 April 2037: No longer long-term UK resident, assuming he has remained non-UK resident throughout.
James moved to Thailand during 2026, but his overseas assets could remain within UK IHT until April 2037.
The important point is that your IHT exit date is calculated by UK tax years, not simply from the day you leave the UK.
Why Two Expats Can Get Different Answers
Sarah spent much of her career overseas before returning to the UK. She was UK resident for 11 of the relevant 20 tax years, then moved permanently to Thailand.
Her IHT tail would normally be three UK tax years, compared with James’s ten.
James and Sarah could move to Thailand on the same day, both become Thai tax resident and both own property here.
Their IHT exit dates would still be very different because their UK residence histories are different.
Already Lived in Thailand for Years?
For some long-established British expats, the April 2025 reforms can produce a clearer and potentially more favourable result.
Under the old rules, worldwide IHT exposure depended heavily on domicile. A British person who retained a UK domicile of origin could remain within UK IHT on their worldwide estate even after living abroad for many years.
The new rules focus instead on UK residence history.
This means someone who has already lived in Thailand for many years may now find that their personally owned Thai and other overseas assets are outside worldwide UK IHT.
Importantly, the April 2025 reforms did not start a new ten-year clock for everyone already living abroad.
After ten consecutive non-UK-resident tax years, earlier UK residence history no longer keeps you within the ordinary long-term UK residence test. If you later return to the UK, however, long-term UK resident status can build up again through your new UK residence history.
You May Not Need to Use the Standard Tail Table
A special transitional rule can apply to some people who were already living outside the UK when the new system began.
If you were not UK domiciled under the old legal rules on 30 October 2024, were non-UK resident in 2025/26 and have not since returned to UK residence, the standard tail table may not apply in the usual way.
Other conditions must also be met, but the result can be an earlier IHT exit date than the standard three-to-ten-year calculation.
Whether you had acquired a non-UK domicile under the old rules is a fact-sensitive legal question. If this may apply to you, your transitional position should be checked separately rather than calculated from your residence dates alone.
What Happened to the Old Three-Year Rule?
You may still come across older articles suggesting that spending three years outside the UK was enough to take your overseas estate outside UK IHT.
That was never a safe general rule for British expats.
Under the old system, the three-year run-off applied to deemed domicile. Someone who remained UK domiciled under the old legal rules could stay within UK IHT on their worldwide estate for much longer.
Since April 2025, the ordinary rules instead use your UK residence history.
A three-year tail can still apply, but generally where you were UK resident for 10 to 13 of the relevant 20 tax years. Longer UK residence produces a longer tail, up to a maximum of ten tax years.
What if You Return to the UK?
Returning to the UK can change your IHT position. The outcome depends partly on how long you have already been non-UK resident.
If You Return before Your Tail Ends
The non-resident years needed to complete your tail must be consecutive.
If you become UK resident before completing them, that run is broken and your position must be recalculated.
For example, if you have completed six years of a seven-year tail, one UK-resident year does not mean you simply have one year left afterwards.
Even a temporary return to the UK, perhaps for work or family reasons, can therefore matter.
If You Return after Ten Non-Resident Years
After ten consecutive non-UK-resident tax years, your earlier UK residence history no longer keeps you within the ordinary long-term UK residence test.
If you later return to the UK, you can build up long-term UK resident status again through your new UK residence history. You do not immediately fall back within the regime simply because of your earlier years in Britain.
If you are considering moving back to the UK, it is worth checking the IHT position before you return.
What Happens When the IHT Tail Ends?
For many long-term expats, the end of the IHT tail can be an important estate-planning date.
Once you are no longer a long-term UK resident, personally owned non-UK assets will generally fall outside UK IHT.
For someone living in Thailand, that could include:
- A personally owned Thai condominium
- Thai bank accounts
- Overseas bank accounts
- Foreign investment portfolios
- Other qualifying non-UK assets
This can also change the planning options available to you. The timing of major gifts, the sale of UK property, where investment assets are held and other restructuring decisions may have a different IHT effect before and after your tail ends.
Reaching the end of the tail does not remove all UK IHT exposure. UK assets can remain within scope, while UK-established pensions can also require separate consideration from April 2027.
Thailand’s Inheritance Tax Position Can Be Much More Favourable
Falling outside UK IHT does not mean your overseas estate simply moves into the Thai inheritance tax regime.
Thailand taxes a much narrower range of inherited assets, including immovable property, securities, bank deposits, registered vehicles and certain other financial assets. For most foreign heirs without Thai nationality or the relevant residence status under Thai immigration law, the charge generally applies only to qualifying assets situated in Thailand.
The tax is paid by the heir rather than the estate, with the THB 100 million threshold applying separately to each heir’s share of each deceased person’s estate. Each taxable heir is responsible for their own liability.
Tax generally applies only above that threshold, at:
- 5% for qualifying ascendants and descendants
- 10% for other taxable heirs
A surviving legal spouse is exempt.
For many expats, this means that once the UK IHT tail ends, some overseas assets may fall outside both UK and Thai inheritance tax.
The two systems can still overlap during the UK IHT tail. There is no specific UK-Thailand inheritance tax treaty, although UK unilateral relief may sometimes reduce double taxation.
What Can Still Remain within UK IHT?
UK-situated assets can remain within UK IHT even after your worldwide IHT exposure has ended.
The clearest example is UK property.
You could therefore have a Thai home, Thai savings and overseas investments outside UK IHT while a house or flat in the UK remains potentially taxable.
Other UK assets, including certain interests linked to UK residential property, can also remain within the IHT regime.
Pensions require separate consideration.
UK Pensions from April 2027
For deaths on or after 6 April 2027, Finance Act 2026 will bring most unused pension funds and pension death benefits into the value of the estate for UK IHT, although registered-scheme death-in-service benefits are excluded.
For someone who is no longer a long-term UK resident, the location of the pension scheme becomes important. For IHT purposes, pension property is broadly treated as situated where the scheme is established.
A pension under a UK-established scheme can therefore remain within UK IHT even after Thai and other overseas assets have fallen outside it.
Pension property under a scheme established outside the UK may instead fall outside UK IHT once the member is no longer a long-term UK resident.
Transferring a UK pension overseas is not automatically a solution. Pension transfers can create separate tax, regulatory and investment consequences.
Other Situations to Check
Some circumstances need separate attention even once you understand your IHT tail.
A Thai or Other Foreign Spouse
Do not assume that everything passing to a Thai or other foreign spouse automatically qualifies for the unlimited spouse exemption.
The issue is not nationality itself. What matters is whether each spouse is a long-term UK resident for IHT purposes.
This can be particularly relevant where the receiving spouse has little or no history of UK residence.
If you are a long-term UK resident but your spouse is not, the normal unlimited spouse exemption can be restricted to the standard nil-rate band, currently £325,000.
That limit is cumulative, so relevant lifetime transfers can use part of it before death.
A non-long-term resident spouse can elect to be treated as long-term UK resident, potentially restoring the unlimited exemption. However, a lifetime election cannot be revoked and can also bring the spouse’s own overseas estate within UK IHT.
For British expats with a Thai or other foreign spouse, particularly where significant assets or pensions are involved, this should form part of the wider estate-planning review.
Trusts
Trusts and other settled assets can follow different IHT rules.
Do not assume that foreign assets held through a trust follow the same treatment as assets you own personally.
Lifetime Gifts
Your long-term UK residence position at the time you make a gift can affect the UK IHT treatment of foreign assets.
Timing can therefore matter if you are approaching the end of your IHT tail.
For someone living in Thailand, significant lifetime gifts should also be checked under the Thai gift-tax rules before any transfer is made.
Work Out Your IHT Exit Date
The first step is to establish when your long-term UK resident status is expected to end.
To do that, you need to know:
- Your last UK-resident tax year
- How many of the 20 tax years ending with that year you were UK resident
- Whether split-year treatment applied when you left
- The length of your IHT tail
- Whether any later UK residence interrupted the required consecutive non-resident years
- Whether the transitional rules could affect your position
Once you know your likely IHT exit date, the next step is to identify what remains within UK IHT before and after it.
That includes considering UK assets, pensions and the position of a Thai or other foreign spouse.
The exit date can then become a useful planning point for decisions such as significant lifetime gifts, selling UK property or restructuring where assets are held.
Not Sure When Your UK IHT Tail Ends?
Understanding your IHT exit date is an important part of wider succession planning for British expats in Thailand.
Expat Tax Thailand can help you review your UK residence history, establish your likely IHT exit date and identify which assets may remain within UK IHT before and after that date.
From there, we can help identify the succession-planning issues that may need attention, including UK property, pensions, significant lifetime gifts, trusts and planning for a Thai or other foreign spouse.
Knowing where you stand can also help you make better-informed decisions about the timing of gifts, property sales, asset ownership and other changes to your estate.
Speak with our Succession Planning team to discuss your position and the next steps.
Download our Succession Planning & Inheritance Guide for Expats in Thailand
