One number that shapes the whole loan
Your down payment is the part of the price you pay in cash at closing, and everything else about the mortgage flows from it: the loan amount is simply the price minus the down payment, and the monthly payment, the interest you will pay over the life of the loan, and whether you owe private mortgage insurance (PMI) are all set by that one split. This calculator keeps the percent and the dollar amount in sync — drag the slider, type a percent, or type a dollar figure, and the other two follow — then shows the loan and the estimated monthly principal and interest at your rate and term.
Where r is the monthly rate (annual rate ÷ 12) and n is the number of monthly payments. Every extra dollar of down payment removes a dollar of loan — and removes the interest that dollar would have cost for decades.
The 20% line and PMI
Put down at least 20% of the price and a conventional loan charges no PMI. Below 20%, lenders add private mortgage insurance to protect themselves — typically a few tenths of a percent of the loan per year, billed monthly — until your balance falls to about 78–80% of the home's value. PMI is not a reason to delay buying forever, but it is a real cost of a small down payment, and this page flags it whenever your down payment is under the line so the trade-off is visible before you commit.
Worked example
On a $350,000 home, 20% down is $70,000, leaving a loan of $280,000. At 6.5% over 30 years the principal and interest payment is about $1,769.79 a month. Drop to 10% down ($35,000) and the loan grows to $315,000, the payment rises to roughly $1,991 a month, and PMI applies on top — the smaller down payment costs more every single month, not just at closing.
How to use this calculator
- Enter the home price you are considering.
- Set the down payment three ways — slider, percent, or dollars — and watch the loan amount update.
- Add the mortgage rate and term to see the monthly principal and interest.
- If the PMI warning appears, compare the payment at 20% down against your budget.
- Run the full picture — taxes, insurance, closing costs — through the Mortgage Calculator and the Closing Cost Calculator.
Bigger is not always better
A larger down payment cuts the payment and total interest, but it also drains cash you may need for closing costs, moving, repairs and an emergency fund. Money locked in home equity is hard to get back out quickly. Many buyers are best served by the smallest down payment that avoids PMI and keeps a healthy cash reserve — use the figures here to find that balance for your own budget, with the Home Affordability Calculator as a cross-check.