# Capital increase: which stock price to use as input to Black-Scholes formula?

For an exercise we have to calculate the theoretical value of a scrip / preferential right on its issue day (23 April) in the context of a capital increase. The scrips are issued on 23 April. The closing price of the stock on that day is 4.70 euro, while the closing price of 22 April is 5.35. A dividend of 0.20 is paid on 23 April. The theoretical equilibrium price is 4.2833 based on the ex-dividend price of 22 April, 5.15 euro.

We have seen the following formula, to calculate the scrip price based on the price of a call option, which in turn we have to calculate through Black-Scholes:

$P(scrip)=(\frac{1}{1+q})*P(calloption)$ with q the dilution factor.

When calculating P(calloption) through Black-Scholes, which price do you use as the current stock price? 5.15? 4.2833? or 4.70?

(If this is not the right place to ask this question, please refer me to the right website)