NEW YORK ( TheStreet) -- It's practically gospel: make your mortgage down payment large enough that you won't have to pay the dreaded private mortgage insurance. But there are times paying PMI is better than the alternative. A period, like today's, of low home prices and bargain-basement mortgage rates can be one of them -- for some buyers. PMI is insurance to protect the lender if you stop making mortgage payments. It's charged if your down payment is less than 20% of the home's value, typically your purchase price. If your equity is larger than that, odds are the lender could sell your home in foreclosure for enough to cover your debt, so PMI is not required. PMI charges depend on the size of your mortgage, down payment and borrower's credit score. With a typical home selling today for $212,100, a borrower with fair credit paying 5% down would be charged about $154 a month for the PMI premium, according to HSH.com, the mortgage data firm. The rate might be only $76 for a buyer with very good credit and a 10% down payment. (HSH has a PMI payment calculator here. about 12% nationwide and more in some hot markets, though many experts think price gains will slow. Mortgage rates have inched up since spring, though they've been fairly flat this fall. Also, PMI is not a life sentence. Under federal law, you have a right to get it canceled once your equity -- current home value minus remaining mortgage debt -- reaches 20%. Rising home prices could get you to that point fairly quickly. Even if increases in home prices are modest, over a number of years your monthly mortgage payments will whittle your debt until you reach that 20% threshold. In the meantime, your PMI payment will likely be deductible on your federal tax return.