How Mortgage Payments Work (Principal and Interest)
Published 2026-11-02
Mortgage calculator is one of the highest-volume money searches in the US. People want a monthly number before they tour a house. The number has two layers: principal and interest (P&I), then extras such as property tax, homeowners insurance and HOA.
Use the free tool
Run these formulas with your own numbers. Math stays in your browser.
Open Mortgage Calculator →Our mortgage calculator shows both. The loan, payment and amortization tools isolate P&I if you already know the financed amount. None of this is a lender quote.
Run the mortgage calculator
Enter home price, down payment, APR and term. Add tax, insurance and HOA if you want a PITI-style total. The page also builds an amortization view so you can see interest fall over time.
The P&I formula
A fixed-rate installment loan uses the standard amortization payment. The monthly rate is APR ÷ 1,200. At 0% the payment is simply principal ÷ months.
r = APR ÷ 1200
Payment = P × r ÷ (1 − (1 + r)^−n)
Each month: interest = balance × r; principal = payment − interest
Why early payments look interest-heavy
Interest is always the current balance times the monthly rate. On a new $240,000 balance at 6%, month 1 interest is $1,200 before a dollar of principal is paid. The same payment later sends more to principal because the balance is smaller. Extra principal — if your servicer applies it that way — only speeds that shift. Confirm there is no prepayment penalty.
| Term | About monthly P&I | What changes |
|---|---|---|
| 15 years | higher payment | less total interest |
| 30 years | lower payment | more total interest |
PITI and escrow
Many US quotes show PITI: principal, interest, tax and insurance. HOA may sit beside that. Escrow is a bucket the servicer pays from — it is not extra interest. Our mortgage tool adds those fields so the total looks like a draft budget, not just P&I.
If you only want the loan math, leave tax and insurance at zero or use the loan calculator. If you want every monthly row, use the amortization calculator.
What a website cannot know
Lenders add points, origination fees, mortgage insurance and day-count rules. A 20% down payment often avoids PMI; less than that usually does not. Property tax is local. Insurance depends on the house and the carrier. Treat the result as a planning range and compare it with the Loan Estimate. “Mortgage calculator” stays near the top of financial search volume because the payment is the first filter on a listing — run two APRs and two down payments in the mortgage calculator before you treat one figure as the budget.
- Start with price and down payment so you know the amount financed.
- Enter the APR you were quoted, not a teaser rate.
- Choose 15, 20 or 30 years (or months on the loan tool).
- Add annual tax and insurance if you want PITI.
- Read P&I, the all-in monthly figure and the interest total.
Use the free tool
Run these formulas with your own numbers. Math stays in your browser.
Open Mortgage Calculator →Frequently Asked Questions
Is the payment the same every month?
P&I is fixed on a fixed-rate loan. Escrow can change when tax or insurance is re-estimated.
Does extra payment cut the required bill?
Usually no. Extra principal shortens the loan and cuts interest if it is applied to principal.
Can I compare 15 vs 30 years here?
Yes. Change the term and read payment versus total interest. The amortization calculator shows the schedule.
Are results a pre-approval?
No. A lender’s underwriting and the Loan Estimate control.
Where is PMI?
This tool does not add private mortgage insurance as its own line. Fold an estimate into insurance if you need it in the total.
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