The Hidden Currency Tax: How Unhedged Global Funds Are Quietly Adding or Removing 1–2% From Your ISA Returns Each Year

Consider two UK investors who both held the same global equity index fund throughout 2022. Both paid the same annual fund charge. Both held exactly the same underlying stocks. Yet their sterling returns differed by approximately 12 percentage points — not because of anything either investor did, but because one held an unhedged version of the fund and the other held a currency-hedged share class. That 12-point gap was generated entirely by sterling's depreciation against the US dollar during that year, which mechanically boosted the unhedged fund's GBP return while the hedged version stripped the currency effect out entirely.

This is the currency dimension of global investing — one of the most significant and least discussed variables in UK retail portfolio construction. The majority of UK investors in HSBC Global Strategy funds, Vanguard LifeStrategy funds, and iShares MSCI World ETFs hold unhedged positions. They are, whether they know it or not, running an active currency position on top of their equity exposure. In years when sterling weakens, that position rewards them. In years when sterling strengthens, it costs them. And the swing between those two outcomes has historically been material — regularly exceeding 1–2% annually, and occasionally far more.

What Currency Exposure Actually Means in Practice

When a UK investor buys a fund that holds US equities, those equities are priced in US dollars. The fund's GBP unit price is calculated by converting the underlying USD asset values into sterling at the prevailing exchange rate. If sterling weakens against the dollar between purchase and sale — i.e., each pound buys fewer dollars — the fund's GBP unit price rises even if the underlying stocks have not moved. Conversely, if sterling strengthens, the GBP unit price falls even if US stocks have appreciated.

This is not a theoretical risk. Sterling has historically been one of the more volatile G10 currencies, subject to significant swings driven by UK-specific political events (the 2016 Brexit referendum, the 2022 mini-budget), Bank of England monetary policy decisions, and global risk sentiment. A currency move of 5–10% within a single calendar year is not unusual for GBP/USD — and given that US equities constitute approximately 65–70% of a typical global equity index, a 10% sterling depreciation mechanically adds roughly 6.5–7% to the GBP return of an unhedged global fund, while a 10% sterling appreciation removes approximately the same amount.

Hedged vs. Unhedged: The Same Fund, Very Different Outcomes

Several major fund providers offer both hedged and unhedged versions of their flagship global funds, allowing a direct comparison of currency impact over defined periods.

Returns sourced from iShares fund factsheets and Vanguard UK fund pages. Figures are approximate total returns in GBP. Past performance is not a reliable indicator of future results.

The 2022 figures are particularly instructive. An investor in the unhedged SWDA lost approximately 8.1% in GBP terms — painful, but reflecting genuine equity market losses partially cushioned by sterling weakness. An investor in the hedged equivalent lost nearly 20% in GBP terms — the full equity market loss with no currency offset. In 2022, being unhedged was significantly better. In 2023, as sterling partially recovered, the hedged investor gained 6 percentage points more than the unhedged investor. Neither outcome was predictable in advance.

The Cost of Currency Hedging

Currency hedging is not free. Hedged share classes typically carry an additional cost of 0.1–0.5% per year, depending on the interest rate differential between sterling and the hedged currency. When UK interest rates are higher than US rates — as has been the case intermittently since 2022 — the cost of hedging GBP/USD is lower, because the hedger benefits from the interest rate carry. When UK rates are lower, the cost of hedging rises.

Beyond the explicit fee, hedging introduces tracking error between the hedged and unhedged versions of the same fund, and in periods of sharp currency movement, the mechanics of rolling hedge contracts can create short-term performance anomalies. Hedged ETFs also tend to have lower trading volumes and wider bid-ask spreads than their unhedged equivalents — a relevant consideration for investors who trade or rebalance frequently.

The practical upshot is that currency hedging is not a free insurance policy. It removes uncertainty but also removes potential upside, and it carries an annual cost that must be weighed against the benefit of currency stability.

Which Major UK ISA Funds Are Unhedged?

The overwhelming majority of mainstream UK ISA funds are unhedged by default. This includes:

• HSBC FTSE All World Index Fund — unhedged, GBP unit price reflects full currency exposure to USD, EUR, JPY and other major currencies
• HSBC Global Strategy Balanced / Dynamic / Cautious — unhedged equity component; bond component may include some currency management within the mandate but is not systematically hedged
• Vanguard LifeStrategy 20%, 60%, 100% Equity — unhedged; currency exposure is a deliberate feature of the fund's global diversification philosophy
• Fidelity Index World Fund — unhedged, tracks MSCI World in GBP without systematic currency hedging
• iShares Core MSCI World UCITS ETF (SWDA) — unhedged; the hedged equivalent is IWDG

For investors who want hedged global equity exposure within an ISA, the options are more limited but available: iShares MSCI World GBP Hedged UCITS ETF (IWDG) is available on Hargreaves Lansdown, AJ Bell, and Interactive Investor. Xtrackers MSCI World GBP Hedged UCITS ETF (XDWG) is available on Interactive Investor and AJ Bell. Both are ISA-eligible (✅) and carry slightly higher OCFs than their unhedged counterparts.

When Does Currency Hedging Actually Make Sense?

The academic literature on currency hedging for long-term equity investors is genuinely mixed. Over very long periods — twenty years or more — currency effects on equity returns tend to partially offset each other, meaning the long-run hedging premium is modest. For investors with a horizon of ten years or more and a high tolerance for year-to-year return volatility, the case for systematic hedging is not compelling.

However, three specific investor profiles have a stronger rationale for considering hedged funds:

1. Investors within five years of drawing down their ISA. Currency volatility in the final accumulation phase can materially affect the terminal value of a portfolio. A 10% sterling appreciation in the year before retirement reduces a £200,000 unhedged global equity ISA by approximately £13,000 in GBP terms — a loss that cannot be recovered if drawdown begins immediately.

2. Investors who are also exposed to sterling weakness through other assets. If your pension, property, and salary are all denominated in sterling, your overall financial position already benefits when sterling weakens (through higher GBP returns on unhedged equity funds). Adding a hedged fund to the mix can reduce the correlation between your investment portfolio and your broader financial position.

3. Investors making large lump-sum contributions near a period of known sterling volatility. A UK general election, a significant Bank of England policy announcement, or a major geopolitical development affecting sterling can create short-term currency dislocations. Hedging a lump-sum contribution during such a window reduces the risk of an adverse currency move immediately after deployment.

Assessing Your Own Currency Position

For most UK ISA investors, the practical first step is simply to understand what currency exposure they currently hold — which most do not. The following approach takes approximately fifteen minutes:

1. List every fund in your ISA and identify whether it is hedged or unhedged (check the fund factsheet — the KIID or PRIIPs document will state this explicitly).
2. Estimate the geographic breakdown of each fund's equity holdings. For a global index fund, approximately 65–70% will be USD-denominated.
3. Multiply your total ISA value by the USD-denominated proportion. That figure represents your effective USD exposure in sterling terms.
4. If sterling appreciates by 5% against the dollar, your GBP return on that USD exposure falls by approximately 5%. If it depreciates by 5%, your GBP return rises by approximately 5%.
5. Decide whether that exposure is intentional and appropriate for your circumstances.

For the majority of long-term ISA investors, the answer will be that unhedged global equity exposure is entirely appropriate and the currency effect is an acceptable source of diversification. For those approaching drawdown or with specific short-term needs, reviewing the hedged alternatives available on their platform is a worthwhile exercise.

The Verdict

Currency exposure is not a hidden fee — it is a genuine risk factor embedded in every unhedged global fund, and whether it helps or hurts your ISA returns in any given year is determined by the foreign exchange market rather than the fund manager. Understanding it, rather than ignoring it, is the minimum standard of informed investing.

This article is for informational purposes only and does not constitute financial advice. Your capital is at risk. Past performance is not a reliable indicator of future results.