Abstract: If you've been making mortgage payments for 10 years on a 30 year mortgage, how much of the loan have you paid off? (Hint: it's less than one-third.) In this talk, we'll see how elementary calculus gives us the tools to build a model of mortgage finance that allows us to answer such questions, and also see what factors influence the answers. The talk will be suitable for students with two semesters of calculus.