International Fisher Effect
This theory predicts that the spot foreign exchange (FX) rate will change over time to reflect and offset differences in interest rates in the respective currencies.
So for example, unhedged currency depreciation losses will on average negate and match exactly any gains on interest differentials between the two currencies.
The International Fisher Effect links Expectations Theory in FX markets with Interest Rate Parity.
Interest rate parity theory predicts that forward FX rates will reflect interest rate differentials.
Expectations Theory predicts that forward FX rates will be reflected - on average - by outturn spot FX rates for the same maturities.
One way of speculating that spot exchange rate will not change by as much as this, is known as an FX carry trade.
Among other things, the International Fisher Effect suggests that it should not be possible to earn consistent profits by entering FX carry trade speculations.
This is because of no-arbitrage theory, which suggests that it should not be possible to earn consistent speculative profits by speculating against Expectations Theory in any market.
