How this calculator works
Each month, interest is the current balance × the monthly rate. The rest of the payment reduces the balance, so the interest share shrinks every month.
The table adds the twelve months of each year together and shows the balance after the last payment of the year.
Extra monthly principal is applied straight to the balance. Because future interest is charged on a smaller balance, the loan ends early and total interest falls.
On a 30-year mortgage, more than half of the first years’ payments typically go to interest; that is normal amortization, not a fee.
Worked example
$300,000 at 6.5% for 30 years
- Monthly payment: $1,896.20.
- Total interest over 30 years: about $382,600.
- Paying an extra $200 a month cuts years off the loan and saves tens of thousands in interest; enter it to see the exact figures.
Questions people ask
Why is so much of my payment interest at first?
Interest is charged on the outstanding balance, which is largest at the start. As the balance falls, more of the same payment goes to principal.
Should I pay extra or invest instead?
Extra payments earn a guaranteed return equal to your loan rate. Investing may earn more but with risk. Many people keep an emergency fund and get any employer 401(k) match first.
Does a biweekly payment help?
Paying half the monthly amount every two weeks makes 26 half-payments, one extra full payment a year, which shortens a 30-year mortgage by several years.
Last reviewed October 2, 2026