The call and put values and the price of the underlying asset are already in present value terms, and the term e(-iT)K = K / (1+i)Tdiscounts the exercise price back to the present at the risk-free rate i (or i = ln(l + i)in continuously compounded returns). As in the binomial model, this equation is enforced through risk-free arbitrage with a replicating portfolio.
Here is the intuition behind the Black-Scholes formula. At expiration, time value is equal to zero and call option value is composed entirely of intrinsic value.
CallT= Max [ 0 , PT – K ]
Prior to expiration, the closing price is a random variable that will not be known until expiration. To value a call option prior to expiration, we need to find the expected value of [PT – K] given the option expires in-the-money (that is, given PT> K). In the Black-Scholes formula, N(d1) is the probability that the call option will expire in-the-money. This probability is shown below.