A swap rate is the difference, either positive or negative, between the forward rate and the spot rate for a particular currency, usually represented by pips.

The formula for calculating the swap rate:

S - spot rate

I1 is the denominated currency rate

I2 is the base currency rate

T - number of days

D - swap rate

Three forms of swap rates：

①When the forward rate is higher than the spot rate, it is called At Premium

②When the forward rate is lower than the spot rate, it is called At Discount

③When the forward rate is the same as the spot rate, it is called At Par

In forex trading usually use the swap rate to mark the price of forward foreign exchange, and report the buy and sell two kinds of swap rate, generally report the third and fourth digit after the decimal point. From the order of the swap rate can be seen on the forward exchange rate is the appreciation or discount. 

In the direct marking method, the swap rates are arranged in order from small to large, that is, the buy swap rate is lower than the sell swap rate, the forward foreign exchange for the appreciation, and vice versa for the discount. 

In the indirect marking method, the swap rate is arranged in order such as from large to small, that is, the selling swap rate is higher than the buying swap rate, forward foreign exchange for the rise, and vice versa for the discount.