How Mortgage Payments Actually Work

A mortgage payment is usually four things bundled together, abbreviated PITI: Principal (the loan balance you're paying down), Interest (the lender's charge on the balance), Taxes (property taxes, collected monthly and held in escrow), and Insurance (homeowner's insurance, also escrowed). Only principal and interest are set by your loan; taxes and insurance vary by location and property and can move your payment year to year even on a fixed-rate loan.

If your down payment is under 20% on a conventional loan, a fifth cost appears: private mortgage insurance (PMI), typically 0.3–1.5% of the loan per year. It protects the lender, not you, and it's why 20% down is the common target. The quoted 'mortgage rate' only covers the interest slice — the actual monthly outlay is meaningfully higher once taxes, insurance, and any PMI are added on top.

Interest is charged on the remaining balance, which is huge at the start, so early payments are mostly interest with only a sliver going to principal. On a $300,000 loan at 7% over 30 years, the first payment of about $1,996 is roughly $1,750 interest and only $246 principal. The mix flips slowly: it can take 18–20 years before more of each payment goes to principal than interest. This front-loading — called amortization — is why selling or refinancing early means you've built little equity.

The payment itself comes from a fixed formula, M = P·[r(1+r)ⁿ] / [(1+r)ⁿ − 1], where P is the loan, r is the monthly rate (annual ÷ 12), and n is the number of payments. You don't need to compute it by hand, but the takeaway is that rate and term dominate the total: stretching 15 years to 30 lowers the monthly payment but can double the lifetime interest.

Because interest tracks the balance, any extra principal early is disproportionately powerful. One common trick: make one extra full payment per year (or split it into 1/12 extra each month). On that $300k/7%/30-year loan, that alone can cut roughly 4–5 years and tens of thousands in interest, because every early dollar of principal erases all the future interest that balance would have accrued.

Two cautions. Confirm your loan has no prepayment penalty (most modern ones don't) and that extra payments are applied to principal, not prepaid interest or escrow. And weigh it against opportunity cost: if your mortgage rate is low, investing the extra money might out-earn the interest you'd save. At today's higher rates, paying down is often the better guaranteed return — but it's a math question the calculator can help you answer.