Loan & Extra Payment Calculator
Calculate monthly loan payments, then see how extra principal or a lump sum changes your payoff time and interest. Free, private and instant.
Extra-payment payoff schedule
| Year | Principal | Interest | Balance |
|---|---|---|---|
| 1 | $5,523.70 | $1,687.69 | $19,476.30 |
| 2 | $5,952.52 | $1,258.87 | $13,523.78 |
| 3 | $6,414.63 | $796.76 | $7,109.16 |
| 4 | $6,912.61 | $298.77 | $196.54 |
| 5 | $196.54 | $1.23 | $0.00 |
Assumes a fixed rate, monthly interest, and that every extra amount reaches principal on the scheduled payment date. Check your contract or servicer for payment-allocation rules and prepayment charges.
Compare your original loan with an early-payoff plan
This free loan extra payment calculator shows your scheduled monthly payment, then calculates what changes if you add recurring extra principal, a one-time lump sum, or both. You can compare the new payoff time, interest saved, total interest, and year-by-year balance without creating an account.
This is a mathematical planning estimate, not financial advice or a lender quote. Check your loan contract and servicer instructions before sending an extra payment.
How to use it
- Enter the loan amount, annual interest rate, and original term.
- Add any extra principal paid each month.
- Optionally enter a one-time extra principal payment and the payment number when it will be made.
- Compare the modeled interest saved and time saved.
- Open the payoff schedule to inspect principal, interest, and ending balance by year.
Use the loan’s interest rate, not its APR. The US Consumer Financial Protection Bureau explains that APR is broader than the interest rate because it can include additional loan fees.
Formula and extra-payment method
For a fixed-rate, monthly-amortizing loan, the scheduled payment is:
payment = P × r × (1+r)^n ÷ ((1+r)^n − 1)
Here, P is the starting principal, r is the annual interest rate divided by
12, and n is the number of monthly payments. Each modeled month calculates
interest on the outstanding balance, applies the scheduled principal, then
applies the selected extra principal. The calculator stops as soon as the
balance reaches zero, so the final payment is not overstated.
This method fits loans where interest is calculated from the outstanding balance. It is not a model for precomputed-interest loans. The CFPB notes that extra payments behave differently under simple-interest and precomputed-interest auto loans.
Assumptions and real-world differences
The result assumes:
- a fixed annual interest rate and monthly payment schedule;
- extra money is received on the scheduled payment date and applied directly to principal;
- no late fees, origination fees, prepayment penalties, or other charges;
- no skipped payments, rate changes, daily-interest timing differences, or lender-specific rounding.
Real servicing rules control the real result, so verify the instructions for your account. For student loans, for example, the CFPB warns that some servicers may credit an overpayment toward a future bill and advises borrowers to check how additional payments will be applied. Some contracts can also include a prepayment charge; for example, the CFPB says not all US mortgages have a prepayment penalty and recommends checking the loan terms.
Why total interest matters
A lower required payment is not automatically a cheaper loan. Stretching the same balance over more years can lower the monthly bill while increasing total interest. Compare the scheduled payment, total interest, and payoff time together—and keep an emergency buffer rather than treating the maximum possible extra payment as a recommendation.
Buying a home instead?
A mortgage can add property tax, home insurance, escrow, mortgage insurance, and HOA fees. Use the mortgage calculator for a broader initial monthly housing-cost estimate.
Frequently asked questions
How is the monthly loan payment calculated?
It uses the standard fixed-rate amortization formula: payment = P × r × (1+r)^n ÷ ((1+r)^n − 1), where P is principal, r is the monthly interest rate, and n is the number of monthly payments. The extra-payment scenario keeps that scheduled payment and applies the selected additional amount to principal.
How much interest can an extra payment save?
It depends on the balance, rate, remaining term, amount, and timing. This calculator runs both schedules and shows the difference. Earlier principal reductions generally have more time to reduce future interest in this monthly-amortization model.
Can I model a one-time lump-sum payment?
Yes. Enter the extra principal and the scheduled payment number when it will be applied. The result combines that lump sum with any recurring monthly extra payment without letting the modeled balance fall below zero.
Should I enter APR or the interest rate?
Enter the loan's annual interest rate. APR can also include lender fees, so using APR as the amortization rate can overstate the modeled interest. Check your loan disclosure for the actual interest rate.
Will my lender apply extra money this way?
Not necessarily. The calculator assumes the extra amount is applied directly to principal on the scheduled payment date and includes no prepayment charge. Confirm payment-allocation instructions, loan type, and possible charges with your lender or servicer.
Is my information saved or uploaded?
No. The calculation runs entirely in your browser. Nothing you enter is uploaded or stored.