How do I run the buy-vs-rent math?

Running the buy-versus-rent math means comparing an actual mortgage payment, including taxes and insurance, against an actual rent for a comparable property, then factoring in how long a buyer plans to stay to see whether buying's upfront costs pay off during that time. A lender or agent can build that comparison using real numbers rather than a rule of thumb someone else's situation produced. Joel Boss runs this exact comparison with buyers before they decide which way to go.