You generally have to pay PMI if you put less than 20 percent down. But not always. The 80/10/10 piggyback mortgage is one way to avoid PMI with only 10 percent down. And special loan programs, usually run by big banks, may let you skip PMI without 20 percent down. But these often have higher interest rates, so weigh the overall costs and savings before moving forward with a no-PMI loan program.