Why does buying a foreign stock make you a currency trader too?
Here is a fact that surprises most people the first time they meet it: if you own a foreign asset, you hold two positions, not one. You own the asset, and you are long the currency it is priced in. You cannot separate them by wishing.
The round trip
A euro-based investor wants to buy US shares. The sequence is unavoidable:
- Sell euros, buy dollars.
- Buy the shares in dollars.
- Later, sell the shares for dollars.
- Sell dollars, buy euros.
Steps 1 and 4 are FX transactions. They happen whether or not the investor thinks about them, and their outcome lands in the final return exactly as firmly as the share price does.
The arithmetic, shown plainly
Start with €10,000 and EUR/USD at 1.0800.
- Convert: 10,000 × 1.0800 = $10,800.
- The US position gains 10%: 10,800 × 1.10 = $11,880.
- A year later EUR/USD is 1.1300 (the euro is stronger, so each euro now costs more dollars).
- Convert back: 11,880 ÷ 1.1300 = €10,513.
Total return in euros: +5.13%, not +10%. The investment did everything it was supposed to do; nearly half the gain was removed by the currency leg.
Run it the other way. Same 10% gain, but EUR/USD ends at 1.0300:
11,880 ÷ 1.0300 = €11,534 — a +15.3% return.
One asset, one performance, two very different outcomes for the holder. The general rule is compact:
Total return = (1 + asset return) × (1 + currency return) − 1
Check it: 1.10 × (1.0800 ÷ 1.1300) − 1 = 1.10 × 0.9557 − 1 = 5.13%. The arithmetic is not an approximation; it is exactly what happened.
Why "hedged" appears in fund names
This is the entire reason you see two versions of the same fund — one hedged, one unhedged. A hedged share class uses currency forwards to strip out step 4's uncertainty, so the investor receives (approximately) the local-currency performance of the underlying market. It costs something, and it removes the outcome in both directions: no currency drag, no currency windfall.
The cost of that hedge has a sign. A hedge is a forward sale of the foreign currency, and a forward is priced off the two short-term interest rates, so a hedged holding earns roughly the asset's local return plus the gap between the home short rate and the foreign short rate. When home rates sit above foreign rates the hedge pays the holder; when they sit below, it charges. A dollar investor hedging euros collects the gap while the Fed's rate is above the ECB's, and a euro investor hedging dollars gives it up. Compare HEFA.US with EFA.US over one year: the difference is the currency move plus that differential, less the hedged fund's extra fee. The second course derives the arithmetic.
Neither version is the correct one. They answer different questions: do I want exposure to this market, or to this market plus its currency? Describing that choice is the job here; making it is the holder's.
The flows this creates
Scale the example up and you have one of the largest sources of FX volume on earth. A pension fund allocating billions abroad generates currency transactions on the way in, on the way out, and continuously in between as it rolls its hedges forward — typically every one to three months, forever. Those rolls are a big part of why FX swaps, not spot trades, are the single largest instrument in the FX market: over 40% of all turnover, versus about 30% for spot.
Most of that volume has nothing to do with anyone's forecast. It is maintenance.
In the data
A price series is always in the currency of the market it trades on, and nothing converts it for you. The US index fund below is priced in dollars; the second chart is the conversion a euro-based holder of it lives with.
Compare two holdings that trade in different currencies without converting one of them first and you have set a return in one currency against a return in another, producing a third number that belongs to neither. The mistake leaves no trace: both lines look like clean percentages.
Try it now
- Measure the fund above first, first bar to last, and write down the return a dollar investor earned over the twelve months.
- Now Measure the currency over the identical window and apply the formula above. The difference between the two numbers is the currency leg — the part of the return that had nothing to do with the companies you owned, and that no equity research note will mention.
- Sign matters more than size here. Say out loud which direction of the second chart helped the euro-based investor, and check yourself: a rising EURUSD means the dollar bought fewer euros at the end than at the start. Same asset, different investor, different answer.