Excel 2010: Loan Interest End Date Calculation

I'm trying to create a formula that will input the maturity date of a particular loan. The spreadsheet contains the interest (fixed rate), the monthly payments, and the current balance of the loan (see below).



The current date will be displayed at the top in a separate cell that we can use to base the maturity date off of, but I guess I just don't understand how to do the math to begin with.

Eventually, I'd like to add a separate sheet with the amortization schedule which could easily just be referenced on this sheet instead of doing all the math here, but if I can understand the math first, I can take it from there.

Any ideas? Thanks in advance.