The criteria of the choice of investment elaborated by theoricians are based on rationality of deciders who after some work often consider two types of aids to investment decision: delay of getting back invested capital and net actualized value. Whereas other forms of aid to funding decision exist. We are proposing in the framework of this article, a new model of aid to funding decision corresponding to the new informal funding. We think that risk capital in the framework of informal funding (Ndjangi) can bring forth long-term funding as strategy, and solutions to questions of rationality of the heads of Small and Medium size Enterprise (SMEs) that prefers the delay of getting back invested capital, solutions to problems of decision of choice, and at last solutions to the quality of profitability of investments.