About this calculator
The monthly payment is only the start. Over a 30-year loan at current rates, you typically pay more in interest than principal. Seeing the total cost clearly is the fastest way to understand how much an extra payment is really worth.
How it works
The standard amortization formula gives the scheduled payment for a fixed-rate loan. With an extra payment entered, the calculator runs a month-by-month amortization to find the new payoff date and the exact interest saved.
Frequently asked questions
How is a monthly mortgage payment calculated?
The standard formula is M = P · r(1+r)ⁿ / ((1+r)ⁿ − 1), where P is the loan principal, r is the monthly interest rate, and n is the number of months. Taxes, insurance, and HOA fees are added on top of this principal and interest figure.
What is the difference between principal and interest?
Principal repays the loan balance and interest is the lender’s fee for lending. Early payments are mostly interest; later payments are mostly principal. That is why extra early payments save so much interest.
How much does an extra $100 per month save?
On a $360,000 loan at 6.5% over 30 years, an extra $100 per month typically removes around 8 years and roughly $55,000 of interest. The earlier you start, the larger the effect.
Should I choose a 15-year or 30-year mortgage?
A 15-year loan has a higher monthly payment but a much lower total interest cost and builds equity faster. A 30-year keeps monthly cash flow flexible. If you can afford the 15-year payment without straining, it is usually the better financial choice.
Does refinancing cost money?
Yes. A refinance involves a new loan with new closing costs, typically 2 to 5% of the loan amount. It pays off only if the new rate is meaningfully lower or you are changing the term to something that suits your cash flow.
What happens if I pay my mortgage early?
Most loans carry a prepayment penalty for a specific window, often the first year. After that, extra payments go to principal and the loan ends sooner. Check your loan agreement for prepayment terms before accelerating.