What extra principal payments change

An extra principal payment is any money you send on top of your scheduled payment and ask the lender to apply to principal. It does not change your interest rate. What it does is lower your balance sooner, so every later month charges interest on a smaller amount. Over time that shortens the loan and cuts total interest.

Why it works

On a fixed-rate loan, each month's interest is the monthly rate times the balance you still owe. Your scheduled payment covers that interest first, and the rest goes to principal. An extra payment goes entirely to principal (if it is applied correctly), so the balance drops faster than the schedule planned. Your next interest charge is a bit smaller, a bit more of your regular payment goes to principal, and the effect builds on itself month after month.

A worked example (illustration only)

These inputs are hypothetical and are not a current market rate: a $250,000 mortgage at 6.75% for 30 years. The scheduled principal-and-interest payment is $1,621.50.

• No extra: 360 payments, total interest $333,738.29, total paid $583,738.29
• $100 extra every month: paid off in 303 payments (57 fewer), total interest $270,999.83, total paid $520,999.83, about $62,738 less interest
• $200 extra every month: paid off in 264 payments (96 fewer), total interest $230,130.62, total paid $480,130.62, about $103,608 less interest

For a shorter loan, the same idea applies on a smaller scale. A hypothetical $30,000 auto loan at 7% for 60 months has a $594.04 payment and $5,642.16 in total interest. Adding $100 a month pays it off in 50 payments with $4,669.83 in total interest (illustration only). The savings are smaller because there are fewer months of interest left to avoid.

What extra payments do not change

• Your required payment. On a typical fixed-rate loan, paying extra does not lower the amount due each month. If you stop the extras, you still owe the original scheduled payment. Some mortgage lenders offer a *recast*, which re-computes a lower payment after a large principal payment, but not every loan or servicer offers one. If you're interested, ask your servicer whether a recast is available on your loan and whether any fee applies.
• Your rate. The rate stays the same. Only a refinance or a loan modification changes it.
• Escrow. On a mortgage, extra principal does not reduce property tax, homeowners insurance, or HOA amounts collected through escrow.

Check these before you prepay

1. Prepayment penalty. Some loans charge a fee for paying off early. The CFPB notes that on mortgages these penalties typically apply when the whole balance is paid off within a set period (for example, by selling or refinancing), and do not normally apply to small extra principal payments, but it advises checking with your lender. Your Loan Estimate shows whether a mortgage has a prepayment penalty. For other loans, check the note or contract.
2. How the servicer applies it. Ask that the extra be applied to principal, not held as an early payment of next month's bill. Check your statement afterward.
3. Your other priorities. Whether to prepay a loan, build savings, or pay off higher-rate debt first depends on your situation. This site shows the arithmetic only and does not recommend one choice over another.

How to test it on this site

Open the loan calculator, or the 30-year mortgage calculator for a mortgage. Enter your loan amount, rate, and term, and note the total interest and the number of payments. Then enter an amount in Extra monthly payment and compare. The payment shown at the top stays the scheduled payment. The calculator adds your extra to principal every month starting in month one, re-runs the schedule, and shows the new payoff date and total interest.

The calculator models a fixed extra amount every month. It does not model one-time lump sums, biweekly schedules, or extras that start partway through the loan. For those, check with your servicer or use the amortization table as a rough guide.

Where to go next

• How amortization works: why the interest share falls over time
• 15-year vs. 30-year mortgage: a shorter term locks in faster payoff instead of relying on voluntary extras
• Auto loan calculator and personal loan calculator

FAQ

• Do extra payments lower my monthly payment? Usually not. They shorten the loan and cut interest, but the required payment stays the same unless you refinance or your lender offers a recast.
• Is it better to pay extra early or late in the loan? Extra paid earlier avoids more months of interest, so on a given loan it usually saves more.
• Can my lender charge me for paying early? Some loans have prepayment penalties. Check your Loan Estimate, Closing Disclosure, or loan contract, and ask the lender.
• Why doesn't the calculator's monthly payment go up when I add an extra? The top figure is the scheduled payment. Your extra is shown separately and applied to principal in the schedule.

Sources (checked 2026-09-25)

• CFPB, "What is a prepayment penalty?" (last reviewed Sep 11, 2024): https://www.consumerfinance.gov/ask-cfpb/what-is-a-prepayment-penalty-en-1957/
• CFPB, "What is a Loan Estimate?" (last reviewed Aug 9, 2024): https://www.consumerfinance.gov/ask-cfpb/what-is-a-loan-estimate-en-1995/

Disclaimer

Estimates only. This page is educational and is not financial, lending, legal, or tax advice. Figures come from the numbers you enter and cover principal and interest only. Your actual loan terms depend on the lender, your credit, and costs such as property taxes, homeowners insurance, PMI, and fees. Before you borrow, get a Loan Estimate or other official disclosure from each lender and compare them. MyLoanCalculator.app is not a lender and does not make loan offers.