A mortgage calculator turns four numbers — home price, down payment, interest rate, and term — into the one figure that actually matters month to month: your payment. But the more useful insight is usually the total interest and how the principal/interest split shifts over the life of the loan. Drag along the balance curve above to watch that split flip: early on, most of each payment is interest; only later does it start meaningfully chipping away at what you owe.
On a $400,000 home with 20% down, you're financing $320,000. At 6.5% over 30 years, the principal & interest payment is about $2,022/mo.
Over the full term that's roughly $408,000 in interest — more than the original loan. Adding just $200/mo extra to principal pays the loan off years early and saves a five-figure sum in interest, which you can see directly by nudging the "extra payment" slider.
Interest is charged on the remaining balance, which is highest at the start. As the balance shrinks, the interest portion of each fixed payment shrinks with it and more goes to principal.
Yes — every dollar down is a dollar you don't finance, plus all the interest it would have accrued. It also lowers your loan-to-value ratio, which can unlock better rates and avoid mortgage insurance.
This models principal, interest, and simple tax/insurance estimates. It doesn't include PMI, closing costs, HOA fees, rate adjustments, or the tax treatment of mortgage interest — your lender's figure is the one to trust.
A 15-year loan pays far less total interest, but the monthly payment is higher. The "right" term depends on cash flow and what else you'd do with the difference — there's no single correct answer.