financial forcasting Model (2)

I have created a community based financial model for a pooling savings and providing loans. I want someone to create me a computer model (visual financial equation or model) that allows me to type in some numbers (variables) and it should work out how long it would take to provide the loan and how long it would take for people to pay back the loans. There are a number of variables and this job is for a mathematician and not just a programmer as I am asking for a financial forecasting model to be created. Please state if you have done something similar before and an example would be great. I don’t mind which software solution is used, even if its as basic as excel as long as it works. Many thanks. Kb.