How this loan calculator works
Enter the amount you plan to borrow, the interest rate (APR) from your offer, the term and the month of your first payment. The calculator applies the standard amortization formula used by banks and credit unions to find a fixed monthly payment that pays the loan off exactly on schedule.
Each month, interest is charged on the remaining balance and the rest of your payment reduces principal. Early payments are mostly interest; later payments are mostly principal. The balance chart and amortization schedule show that shift month by month and year by year.
Add an optional extra payment to see how sending a little more toward principal shortens the loan and cuts total interest. Turn on Compare to place two terms side by side — for example, a five-year loan against a three-year loan.
The loan payment formula
Fixed-rate installment loans use the standard amortization formula, which sets one payment that clears interest and principal exactly by the final month:
M = P × [ r(1 + r)^n ] / [ (1 + r)^n − 1 ]
- M = monthly payment
- P = amount financed
- r = monthly interest rate (APR ÷ 12)
- n = number of monthly payments (years × 12)
- Each month: interest = balance × r; principal = M − interest (+ any extra payment)
Worked example
Suppose you borrow $25,000 at 9% APR for five years. The monthly rate is 0.75% and there are 60 payments, so the formula gives a payment of about $519. Over the life of the loan you pay roughly $6,137 in interest, for a total of about $31,137.
Add $100 a month to that payment and the loan is paid off about 11 months early, saving roughly $1,240 in interest. Shorten the term to three years instead and the payment rises to about $795, but total interest falls to around $3,620.
What a loan payment is made of
Every installment payment has two parts: interest, which is the lender's charge for the money you still owe, and principal, which actually reduces the debt. Because interest is calculated on the outstanding balance, it is highest at the start. On a five-year loan at 9%, the first payment of $519 includes about $188 of interest; by the final year, interest is under $25 a month.
This front-loading is why paying extra early has an outsized effect. A dollar of principal repaid in month three stops generating interest for the remaining fifty-seven months, while the same dollar repaid in month fifty-five saves almost nothing.
APR versus interest rate
The interest rate is the annual cost of borrowing the principal. The annual percentage rate (APR) also folds in most mandatory lender fees, such as origination fees, and spreads them over the term. Under the federal Truth in Lending Act, lenders must disclose the APR before you sign, which makes it the fairest number for comparing offers.
If a lender deducts an origination fee from your proceeds, you receive less cash than you repay. When comparing a loan with a fee against one without, use APR, and make sure the amount you borrow covers what you actually need after the fee.
How the term changes the real cost
A longer term lowers the monthly payment but almost always raises total interest, both because you borrow for longer and because lenders often charge higher rates on longer terms. A shorter term demands more each month but builds equity faster and finishes sooner.
A useful rule: choose the shortest term whose payment fits comfortably in your budget with room to spare for savings. If cash flow is uncertain, a longer term with voluntary extra payments gives you flexibility — as long as the loan has no prepayment penalty.
Smart ways to pay less interest
Shop at least three lenders, including a credit union, on the same day so offers are comparable. Credit scoring models generally treat several inquiries for the same type of installment loan within a short window as a single inquiry.
Improve your credit before applying where you can: paying card balances below 30% of their limits and fixing report errors can move you into a better pricing tier. Ask about autopay discounts, which are commonly 0.25 percentage points. After you borrow, round your payment up or apply windfalls such as tax refunds directly to principal, and confirm with the lender that extra money is applied to principal rather than to future payments.
Before you sign
Read the loan agreement for prepayment penalties, late-fee terms and whether the rate is truly fixed. Make sure the payment fits a realistic budget that still includes an emergency fund; a missed payment can cost more than any rate difference. Use the amortization schedule here to check the lender's figures — the monthly payment and total interest should match within a few dollars.
Frequently asked questions
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Open calculatorNot financial advice. ClearCalc provides estimates for educational purposes only. Results depend on the assumptions you enter and may differ from offers from lenders or institutions. Consult a qualified professional before making financial decisions.