This page answers one question: what is monthly principal and interest on a fixed US mortgage. Enter the amount you borrowed (price minus down payment, plus any closing costs you rolled in), the APR, and the term in years. The result is monthly P&I, the number of months, total paid, and total interest. It is not PITI and it is not a Loan Estimate.
A worked case from the tests: $400,000 at 6.5% for 30 years. Monthly P&I is about $2,528. The term is 360 months. That $2,528 is the note. It does not know your county tax bill or your insurer.
A second case from this engine: $350,000 at 6.5% for 30 years is $2,212.24 a month. Total paid if you keep all 360 drafts is $796,406.40. Interest is $446,406.40. Cut the rate to 5.75% and keep 30 years: $2,042.50 a month, $735,300.00 total, $385,300.00 interest. The half-point saves $169.74 a month and $61,106.40 of interest. Keep 6.5% but shorten to 15 years: $3,048.88 a month, $198,798.40 of interest. Cash-flow got harder. Lifetime interest got much smaller. Run those three inputs on this page if you want to see the same dollars.
Why the draft on your account is larger
Most first-lien loans collect property tax and homeowners insurance in escrow. The servicer pays the county and the carrier. Your debit is P&I plus 1/12 of those bills, plus a small cushion. Escrow analysis once a year can raise or lower the draft even if the note never changed. PMI often sits on top when you put less than 20% down. FHA, VA, and credit-union products have their own insurance rules. None of that is in this formula.
The formula is M = P × r(1+r)^n / ((1+r)^n − 1), with r as monthly APR and n as months. Banks use the same math for the note. Extra principal on a 30-year note is optional and is not a field on this form. A 15-year contractual payment is not optional. Compare a rate cut to a shorter term on the matching guide; this page only prices one note at a time.
Affordability is not this number alone
Lenders use debt-to-income on PITI plus other debts. You should use a budget: leftover income after PITI, HOA, and a reserve. Run this page for P&I, add a county tax estimate and an insurance quote, then compare the sum to take-home from the paycheck or 1099 tool.
We are not a lender. There is no application on this site. The Loan Estimate still wins for the closing number. Ads load only after you calculate. A half-point on a long term is a large interest pile; run the page twice and subtract if you are shopping a rate, not a house price.