远期贴水是远期升水的相对概念，是指远期汇率低于即期汇率。

In a foreign exchange situation where the domestic current spot exchange rate is trading at a higher level than the current domestic futures spot rate for a maturity period. A forward discount is an indication by the market that the current domestic exchange rate is going to depreciate in value against another currency.

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The equilibrium that results from the relationship between forward and spot exchange rates within the context of covered interest rate parity is responsible for eliminating or correcting for market inefficiencies that would create potential for arbitrage profits. As such, arbitrage opportunities are fleeting. In order for this equilibrium to hold under differences in interest rates between two countries, the forward exchange rate must generally differ from the spot exchange rate, such that a no-arbitrage condition is sustained. Therefore, the forward rate is said to contain a premium or discount, reflecting the interest rate differential between two countries. The following equations demonstrate how the forward premium or discount is calculated.

The forward exchange rate differs by a premium or discount of the spot exchange rate:

http://upload.wikimedia.org/math/0/3/2/03274a53626f8d4f7591b0ea33286052.pngpremium or discount 远期升水/贴水" />

where

P is the premium (if positive) or discount (if negative)

The equation can be rearranged as follows to solve for the forward premium/discount:

http://upload.wikimedia.org/math/4/4/8/4483ad8ff98447b56235a0f19b3a8fb2.pngpremium or discount 远期升水/贴水" />

In practice, forward premiums and discounts are quoted as annualized percentage deviations from the spot exchange rate, in which case it is necessary to account for the number of days to delivery as in the following example.^[2]

http://upload.wikimedia.org/math/9/a/9/9a986e1f45dd0999f8eae7b838332125.pngpremium or discount 远期升水/贴水" />

where

N represents the maturity of a given forward exchange rate quote

d represents the number of days to delivery

For example, to calculate the 6-month forward premium or discount for the euro versus the dollar deliverable in 30 days, given a spot rate quote of 1.2238 $/€ and a 6-month forward rate quote of 1.2260 $/€:

http://upload.wikimedia.org/math/e/6/6/e66357255c91646c1713e58c8b19f0dc.pngpremium or discount 远期升水/贴水" />

The resulting 0.021572 is positive, so one would say that the euro is trading at a 0.021572 or 2.16% premium against the dollar for delivery in 30 days. Conversely, if one were to work this example in euro terms rather than dollar terms, the perspective would be reversed and one would say that the dollar is trading at a discount against the euro.