Percentage cost of offering/accepting a discount

Hi sir, I had a doubt regarding the formula to be used to calculate this. For the simple annual percentage cost in the context of accepting a discount from a supplier, its simply (discount received/amount paid if discount is taken)* (number of days in the year/difference between normal payment days and payment days if discount is taken) right? However for the effective annual rate of the discount, BPP and Kaplan have given different formulas: BPP: (1+r)^(number of days in the year/difference between normal payment days and payment days if discount is taken) Kaplan: (1+(discount/amount paid if discount is taken))^ (number of days in the year/difference between normal payment days and payment days if discount is taken) - 1 Both formulas give different answers, please clarify which one should be used In which context. Thank you!