Progressive Current Accounts: Profit-Sharing Interest

Certain financial investments have different profitabilities according to the invested capital. In particular, there are some bank transactions, such as progressive current accounts, which discriminate nominal rates of interest, depending on the invested sums, that is, transactions whose underlying financial laws are not homogeneous of the first degree with respect to the amounts. More specifically, this discrimination occurs when assigning an equal rate to the capitals C in the same interval ]Ci,Ci+1]. This makes the financial law discontinuous with finite jumps, once the term has been fixed. Of course, it would be convenient, for a group of investors, to join their savings because greater rates of interest can be obtained. The question is how to distribute, in a rational way or with equity, among the individual agents, the interest obtained jointly. Our findings are based on a progressive sharing, using differential calculus.