Mechanism: what carry trade is (and what it is not)
Carry trade is a currency strategy that seeks to benefit from the interest-rate difference between two currencies while holding a position. In simplified terms, if one currency has a higher interest rate than another, the trade aims to earn “carry” (the differential) and offset it against the effect of exchange-rate changes.
A common misunderstanding is treating the interest-rate differential as a stand-alone profit engine. In practice, the realized outcome depends on multiple moving parts: interest-rate levels, how long you hold, the path of exchange rates during that period, and all costs involved (for example, financing, spreads, and execution frictions).
Common mistakes and what they can do
1) Assuming the interest differential automatically “wins”
A frequent error is expecting the higher-yield currency to stay stable relative to the funding currency. When the exchange rate moves enough against the position, the carry can be reduced or overwhelmed. This failure mode is common in periods of abrupt repricing, where “high yield” can become “high loss” even if the starting interest-rate gap looked attractive.
2) Ignoring the full cost picture
Another mistake is focusing only on the headline interest difference and leaving out costs that can materially affect results. These may include transaction costs, wider-than-expected bid/ask spreads, financing-related charges, and operational frictions from rebalancing or rolling positions. If costs scale with trade frequency or size, outcomes can differ sharply from a cost-free back-of-the-envelope estimate.
3) Using a single scenario without stating assumptions
Many people run examples that implicitly assume constant rates, constant spreads, and smooth exchange-rate behavior. If the holding period is longer, the path matters more than the start and end. A neutral approach is to write down assumptions explicitly: start/entry conditions, assumed holding duration, whether the position is rolled, and which costs are included.
4) Confusing historical relationships with future results
Even when the strategy appears to have worked in some past regimes, that does not establish that it will work again. The link between yield differentials and exchange rates can change when market volatility rises, funding conditions tighten, or risk appetite shifts.
5) Overlooking material limitations and failure modes
At least one limitation is structural: exchange-rate risk can dominate carry. Another limitation is that results can be sensitive to leverage and to liquidity conditions that affect execution quality. These sensitivities mean outcomes vary with market conditions, costs, and operational factors rather than following a smooth, predictable path.
Verification: neutral checks you can do independently
Build a “carry vs FX move” sensitivity list
Write a short list of the key variables that determine payoff: the interest-rate differential, the holding period, expected and adverse exchange-rate moves, and total costs. Then ask: if the exchange rate moves modestly or sharply against the position, how much of the carry is left?
Include execution and cost placeholders
If you lack exact numbers, use neutral placeholders and compare outcomes under multiple cost assumptions (low/medium/high). The goal is not precision; it is confirming whether the concept still holds when costs and frictions are non-trivial.
Use scenario ranges, not one-point estimates
Instead of a single calculation, test a small set of scenarios that reflect different volatility regimes and different lengths of holding. This helps prevent the common mistake of believing one favorable example generalizes.
If you want, share the version of carry trade you mean (for example, how you define financing/rolls and what instruments you use), and a checklist can be tailored to your definition without turning it into a trade recommendation.