What “rebasing” would mean
Rebasing means replacing an asset’s historic tax cost with its market value on a specified date. If a portfolio bought for £300,000-equivalent were worth £500,000 on arrival and genuinely rebased, only growth above £500,000 would normally form the starting point for a later gain.
That sounds intuitive: the growth happened while the investor lived in Dubai, so why would the UK care about it? But UK Capital Gains Tax does not generally divide an investment’s growth at the date somebody arrives. Residence determines whether a disposal is within charge; it does not normally rewrite the asset’s acquisition history.
How the UK normally calculates the gain
For a straightforward investment held personally, the broad calculation is disposal proceeds less allowable acquisition cost and relevant costs. Pooling and share-identification rules can affect the detail where the same shares or units were bought in several transactions.
For a foreign-currency investment, HMRC’s approach is not to calculate the gain entirely in dollars or euros and translate the final answer. The acquisition amount is normally converted to sterling at the exchange rate applying when the investment was bought. The disposal proceeds are converted at the rate applying when it is sold.
| Transaction | US-dollar position | Sterling tax input |
|---|---|---|
| Purchase in Dubai | $400,000 | £250,000 at the acquisition-date rate |
| Value on UK arrival | $500,000 | Useful evidence, but not a general new base cost |
| Later sale in the UK | $520,000 | £400,000 at the disposal-date rate |
| Indicative gain | $120,000 in dollar terms | £150,000 before costs and reliefs |
This simplified example shows why the platform’s performance figure is not the UK tax computation. The investment rose by $120,000, but sterling also weakened between purchase and sale. The resulting sterling gain is larger. The opposite currency movement could reduce the gain or create a sterling loss.
The arrival valuation still matters
Even though it does not normally become the tax base cost, keep a complete valuation at the point UK residence begins. It helps distinguish pre-arrival and post-arrival performance, supports advice and portfolio decisions, and may be relevant if a specific relief or product rule needs an arrival value.
It is also valuable evidence if records later become difficult to retrieve. But labelling an arrival valuation “rebased cost” on a spreadsheet does not make it the statutory base cost.
The four-year FIG regime is relief—not rebasing
A person returning after at least ten consecutive tax years of non-UK residence may qualify for the four-year foreign income and gains regime. During the first four tax years of UK residence, a qualifying new resident can claim relief on eligible foreign gains.
That may protect a qualifying gain realised after arrival, including a gain calculated from the historic acquisition cost. But the mechanics remain important: the gain is calculated and reported, then the identified qualifying foreign gain is relieved through a claim. The asset has not been rebased.
A FIG claim is not automatic. It is made for the relevant year and identified income or gains. Claiming means losing the UK personal allowance and Capital Gains Tax annual exempt amount for that year, so the value of the relief must be compared with the allowances surrendered.
A short absence creates a different risk
If you previously lived in the UK, moved to Dubai and return after a comparatively short period, temporary non-residence may be more important than rebasing.
Where the statutory conditions are met and the non-UK residence period does not exceed five years, certain gains realised while abroad can be treated as arising in the tax year of return. The regime commonly matters for assets owned before departure. A sale in Dubai therefore does not automatically create a clean new history.
By contrast, assets acquired after departure and sold during the non-resident period are generally outside the capital-gains clawback, subject to important exceptions. The asset timeline—bought before leaving, bought abroad, sold abroad or retained on return—must be reconstructed before any “reset” conclusion is reached.
Selling and buying again can establish a new cost—but it is a transaction
A genuine disposal followed by a new acquisition can create a new commercial purchase price for the new holding. That is not automatic rebasing: it involves selling an asset, crystallising whatever tax treatment applies to that disposal, paying transaction and currency costs, and accepting market risk while reinvesting.
The sequence must also be checked against temporary non-residence and the UK’s share-identification rules, including same-day and 30-day matching where relevant. Selling and immediately buying the same line back should never be presented as a guaranteed tax reset.
Sometimes the better answer is selective: realise one holding with poor UK tax status, retain another that is already suitable, and deal separately with wrappers or products that are not taxed under ordinary capital-gains rules.
Not every investment follows the capital-gains calculation
The word “portfolio” can hide several different tax regimes. Before discussing base cost, establish what is legally owned.
- A direct share or UK-reporting offshore fund will commonly produce a capital gain or loss on disposal.
- A non-reporting offshore fund will normally produce an offshore income gain taxed as income, not an ordinary capital gain.
- An offshore investment bond is generally assessed through the chargeable-event regime rather than by rebasing each underlying fund.
- Pensions and overseas retirement arrangements have their own scheme, treaty and benefit rules.
- Employee shares, options and structured products can carry income-tax consequences that a platform valuation does not reveal.
When market value really can be relevant
There are specific situations in UK tax law where market value replaces or modifies historic cost. Examples can include assets acquired on death, certain transactions that are not at arm’s length, and statutory rebasing rules for particular categories such as non-resident disposals of UK land.
Those are targeted rules with their own conditions and dates. They should not be generalised into “all overseas investments rebase when I move to Britain”. A transfer between spouses or civil partners can also be tax-deferred under no-gain/no-loss rules, but that usually carries the existing base cost forward rather than creating a fresh market value.
A practical return-to-UK example
A British couple bought an Irish-domiciled global ETF for $600,000 while living in Dubai. It is worth $850,000 when they return to the UK and $900,000 when they later consider selling.
The £-equivalent value on the return date does not normally become their new tax cost. The calculation may refer back to the sterling value of each original acquisition, adjusted for relevant costs and any later purchases or sales. The ETF’s UK reporting status must also be confirmed for the exact share class and relevant periods.
If they had been non-UK resident for at least ten consecutive tax years, a valid FIG claim might relieve a qualifying foreign gain during their available window. If their time abroad was short, temporary non-residence and the pre-departure history would need testing instead. Same investment; very different planning sequence.
The records to preserve before the move
| Record | Why it matters |
|---|---|
| Original acquisitions | Contract notes, dates, quantities, price and transaction fees for every purchase. |
| Corporate actions | Splits, mergers, dividends reinvested, rights issues, switches and transfers. |
| Fund identity | Full legal name, ISIN, share class and UK reporting-status history. |
| Currency evidence | Transaction currency and a consistent, supportable exchange-rate source. |
| Arrival snapshot | A full valuation on the residence or split-year boundary—kept as evidence, not assumed rebasing. |
| Product terms | Policy documents, surrender values, guarantees and provider confirmation of UK servicing. |
| Residence timeline | Departure and return dates, travel calendar, homes, work and family ties. |
The planning point
Do not build a return-to-UK plan around an assumed tax reset that does not exist. Establish the residence date, reconstruct the original cost, translate the transactions correctly, classify every holding and then test the available reliefs.
The strongest outcome is not simply the lowest tax number. It is a portable portfolio with clean records, the right UK tax characteristics and a clear job within the life you are returning to build.
