Your US stock gained 10%. Your home-currency return may not

Write the exchange rate in one direction

Suppose a hypothetical investor spends 1,000 units of home currency to buy an asset worth $1,000 when each dollar costs one home-currency unit. The asset rises to $1,100. If each dollar now converts into only 0.90 home-currency units, the holding is worth 990 at home: a 1% loss despite a 10% dollar gain.

The combined return is 1.10 multiplied by 0.90, minus one. Adding 10% and minus 10% would incorrectly produce zero because it ignores the interaction. The direction of the quote matters: “home currency per dollar” and “dollars per home currency” are reciprocals, so their percentage changes cannot be used interchangeably.

Separate investment performance from conversion costs

The market exchange rate shown in a headline is not necessarily the rate applied to a retail conversion. A broker or bank can include a spread or explicit fee. Small recurring purchases may face a different effective conversion cost from one larger transaction, depending on the provider’s schedule.

For a clean record, save asset purchase and sale values, the exchange rate actually applied and all fees. If you receive dividends, those cash flows may have different conversion dates from the final sale. A single start-to-finish exchange-rate calculation is a useful simplification, not an exact reconstruction of every multi-transaction portfolio.

Listing currency is not the whole exposure

A company listed in dollars can earn revenue and incur costs in many currencies. Its business exposure is therefore different from the currency used to buy its shares. A fund’s trading currency also does not prove that its underlying foreign-currency exposure has been hedged.

A hedged share class attempts to offset specified currency effects through a defined strategy, but implementation, costs and imperfect matching can affect results. Read the prospectus instead of assuming the word “USD” in a fund name describes every relevant risk. Currency protection is not the same as protection from a fall in the underlying assets.

Compare results against the right benchmark

If your statement reports returns in home currency, compare them with a benchmark expressed on a compatible currency and total-return basis. Comparing a home-currency portfolio including dividends with a dollar price-only index mixes two differences at once. That makes it difficult to tell whether asset selection or currency explains the gap.

This framework is also useful when reading claims that a stronger dollar helps or hurts everyone. Importers, exporters, foreign borrowers and investors can have different exposures. Start with the actual cash flows and their currencies. For personal portfolio arithmetic, keep a one-line identity: home value equals foreign asset value multiplied by home-currency units per foreign unit. Once that identity is clear, the competing headlines become much easier to check.

A foreign investment gives the household two moving parts even when the account shows one final number. Keeping the asset return and currency effect on separate lines makes it easier to see what actually helped or hurt.