Mortgage Prepayment Calculator: See How Extra Payments Change Your Entire Loan

How mortgage prepayment works behind the scenes

When you make your regular monthly payment, a portion goes to interest and the rest to principal. Early in the loan, interest dominates — on a $280,000 loan at 6.5%, your first payment of $1,770 splits into roughly $1,517 interest and only $253 principal. That's 86% interest.

An extra payment goes entirely to principal. When you add $300 to that first month's payment, the full $300 reduces your balance immediately. Next month, interest is calculated on a balance that's $300 lower, so slightly more of your regular payment goes to principal. This snowball effect compounds over years, and it's why even modest prepayments produce outsized results.

Our amortization guide visualizes this shift month by month if you want to see exactly how the interest-to-principal ratio changes over time.

What happens when you prepay: real scenarios

Numbers make this concrete. Here's a $280,000 mortgage at 6.5% with various extra payment levels, all starting from month one:

Look at the $100/month row. You pay $30,980 in total extra payments but save $38,200 in interest — a net benefit of $7,220. That's a 23% return on your extra money, guaranteed, with zero market risk. The return ratio improves at higher amounts because the compounding effect gets stronger.

Calculate your exact numbers with the extra payment calculator.

When prepayment makes the most impact

Timing matters almost as much as the amount. The same extra payment produces dramatically different results depending on when you start.

The first five years are golden

Because interest charges are highest early in the loan, prepayments during years 1 through 5 have the longest compounding runway. $200 extra per month starting in year 1 saves roughly $63,700 on our example loan. Starting the same extra payment in year 10 saves about $34,100. Same effort, half the result — just because of timing.

Don't wait for a perfect amount

People often delay prepayment because they feel the amount they can afford is "too small." Even $50 per month saves $15,400 on a $280,000 loan at 6.5% and cuts 2 years off the term. There is no minimum threshold for prepayment to be worthwhile. Every dollar applied to principal reduces interest from that day forward.

Prepayment vs other financial moves

Before committing extra cash to your mortgage, run through this quick priority list:

Higher-interest debt first. If you have credit card balances at 18-24%, paying those down produces a bigger guaranteed return than prepaying a 6.5% mortgage. Knock out the expensive debt before accelerating mortgage payments.

Emergency fund second. Keep three to six months of expenses accessible. Prepaying your mortgage is irreversible — you can't easily get that money back in an emergency without refinancing or selling.

Employer match third. If your employer matches 401(k) contributions and you're not maxing the match, that's a 50-100% guaranteed return. Capture the full match before increasing mortgage prepayments.

Then prepay. Once high-interest debt is gone, the emergency fund is solid, and you're capturing employer matches, putting extra toward the mortgage is one of the best risk-free investments available. The comparison between prepaying and investing in the market is explored in depth in our overpayment decision guide.

Watch out for prepayment penalties

Most conventional U.S. mortgages allow unlimited prepayment with no penalty. But some loans — particularly those originated before 2014, certain ARMs, and subprime products — include prepayment penalty clauses. These can charge you 1-3% of the remaining balance or a set number of months' interest if you pay off early.

Before starting any prepayment strategy, check your loan documents or call your servicer. Ask specifically: "Does my loan have a prepayment penalty?" Our penalty guide covers the details of what to look for and how penalties are structured.

According to CFPB rules, qualified mortgages originated after January 2014 cannot include prepayment penalties, which covers the majority of loans on the market today.