Estimate your monthly private mortgage insurance (PMI) when your down payment is under 20%, and see how it fits into your total payment. PMI is added automatically while your loan-to-value is above 80%.
Lenders require PMI on conventional loans when your down payment is under 20% (loan-to-value above 80%). It protects the lender, not you.
You can request cancellation at 80% LTV, and it automatically terminates at 78% LTV based on the original schedule. Paying extra principal gets you there faster.