How currency hedging works
Currency hedging uses financial instruments — most commonly forward contracts — to lock in an exchange rate today for a transaction that will happen in the future. By fixing the rate, you remove uncertainty about how much foreign currency will cost (or earn) you in your home currency.
The hedge ratio lets you decide how much of the exposure to lock in: 100% removes all FX risk on that exposure but also removes any upside if rates move favorably. Lower ratios keep some skin in the game.