If you buy a house with less than 20% down, you're likely going to pay PMI (private mortgage insurance). It's an insurance policy for the lender just in case you default on the loan.
PMI is applied to conventional loans when you don't have 20% equity in the home. It's automatically canceled once you reach 22%. But that can take up to 6.5 years of regular mortgage payments.
PMI is calculated as a percent of the purchase price as set by the lender. It can range from 0.58% to 1.86% of the loan. There are several online calculators to help get an estimate.
Basically you need a down payment of 20% or more or you have a high-interest loan. Some people take out a second loan to make a larger downpayment then pay down that loan quicker.
It's automatically removed once you reach 20% equity in the home. Or you can have your home audited to show that you have reached 22% equity. Lastly, you can refinance.