Insurance lenders require when your down payment is under 20%, protecting them if you default.
PMI is an extra monthly cost lenders charge on conventional loans when the down payment is less than 20%, protecting the lender — not you — against default. It can usually be removed once your equity reaches 20% to 22% of the home's value. Avoiding or eliminating PMI lowers your effective cost of owning.
Putting down 20% on a conventional loan avoids PMI entirely.