below the strike price, the holder of the put has the right, but not the obligation, to sell the asset at the strike price, while the seller of the put has the obligation to purchase the asset at the strike price if the owner uses the right to do so (the holder is said to exercise the option). In this way the buyer of the put will receive at least the strike price specified, even if the asset is currently worthless.

If the strike is , and at time the value of the underlying is , then in an American option the buyer can exercise the put