A mortgage calculator condenses a 30-year financial commitment into a single monthly number. Understanding what that number contains will help you read it like a lender does.
The four parts of a payment
Principal pays down what you borrowed. Interest is the cost of borrowing that money. In most places taxes and insurance are collected monthly into an escrow account — the bank pays them for you when they are due. On early payments the vast majority of the payment is interest; only later does principal take the lead.
Where the formula comes from
Monthly payment = P × r × (1 + r)^n / ((1 + r)^n − 1), where P is the loan amount, r the monthly rate (annual ÷ 12) and n the total number of payments. This is the standard amortization formula lenders use to keep the payment equal every month while the interest-to-principal split changes.
Read the right numbers
Most people only look at the monthly payment. The more revealing figure is total interest — the difference between what you pay and what you borrowed. Our calculator shows both, plus what a small extra monthly payment does to the term.
Remember that the quoted APR rarely tells the full story: down payment, closing costs and the interest rate all interact. A 6% rate on 30 years with 5% down is a very different loan than 6% with 20% down — because the amount financed differs.
Use the output responsibly
A calculator is a planning tool, not a promise. Rates move daily and lenders add fees you cannot see in a formula. Use the result to set a budget range, then talk to a lender for a real quote.