How does the calculator turn a rate and term into a payment?
The calculator first converts the annual rate into a monthly rate by dividing by 12, then counts the payments: years times 12. Those two numbers and the loan amount go into the standard amortization formula, which finds the one payment that, made every month, brings the balance to exactly zero on schedule.
Inside each payment, interest is charged on whatever balance is left that month, and the rest of the payment reduces principal. Because the balance is largest at the start, early payments carry the most interest. The payment itself never changes on a fixed-rate loan; only its split does.
Total interest is the payment multiplied by the number of payments, minus the amount borrowed. Total cost is simply all the payments added together. Neither figure includes fees billed separately or charges deducted from your loan proceeds.
M = P × r × (1 + r)^n ÷ ((1 + r)^n − 1) Total interest = M × n − P
- M
- fixed monthly payment
- P
- loan amount (principal)
- r
- monthly interest rate (annual rate ÷ 12, as a decimal)
- n
- number of monthly payments (years × 12)
Example: an $18,000 personal loan at 11.25% for 4 years
Scenario: Say you borrow $18,000 to replace a roof, at an illustrative 11.25% fixed rate, repaid monthly over 4 years. Payments are made at the end of each month.
- Monthly rate11.25% ÷ 12 = 0.9375% (0.009375)
- Number of payments4 years × 12 = 48 payments
- Monthly payment$18,000 × 0.009375 × 1.009375^48 ÷ (1.009375^48 − 1) = $467.41
- First month's splitInterest $18,000 × 0.009375 = $168.75; principal $467.41 − $168.75 = $298.66
- Total paid$467.41 × 48 = $22,435.68
- Total interest$22,435.68 − $18,000 = $4,435.68
You would pay $467.41 a month and about $4,435.68 in interest, for a total of $22,435.68.
Lenders round the final payment, so your last bill may differ by a few cents; any origination fee would be extra.
When is a basic loan calculator the right tool?
Sizing a personal loan before you apply
Run the amount you actually need, not the maximum you might be approved for. Seeing the payment first helps you decide whether to borrow less or wait.
Checking a lender's quote
Enter the rate and term from a loan offer to confirm the payment it shows. If the numbers do not match, ask whether fees were added to the balance or the rate is variable.
Choosing between terms
Lenders often offer the same loan over several terms. Running each one shows the trade between a lighter monthly payment and a larger interest bill.
Budgeting for a fixed expense
For a planned purchase such as a repair or medical bill, the payment tells you how much monthly room the loan will take for the full term.
What mistakes skew a loan payment estimate?
Using the APR as the interest rate
The APR folds fees into a yearly rate, so entering it here overstates the payment slightly. Use the note rate for the payment and the APR for comparing offers.
Forgetting a deducted origination fee
If a fee comes out of the proceeds, you repay the full loan amount but receive less cash. Borrowing a little more to cover it raises the payment and the interest.
Judging a loan by its payment alone
A lower payment often just means more months. Look at total interest before deciding a longer term is the better deal.
Assuming a variable rate stays put
This calculator holds the rate fixed. If your loan can adjust, rerun the numbers at a higher rate to see how much room your budget needs.
Rounding the term in your head
A 54-month loan is 4.5 years, not 4 or 5. Enter the actual term so the payment and the interest are not off by hundreds of dollars.
How much does stretching the term really cost?
Stretching the same $18,000 at 11.25% from 4 to 6 years drops the payment from $467.41 to $344.92, but total interest rises from $4,435.68 to $6,834.24. The 3-year version costs $591.43 a month and only $3,291.48 in interest.
The pattern holds at any rate: each extra year adds months of interest on a balance that is paying down more slowly. If a lower payment is what makes the loan affordable, it can still be worth it, but it helps to know the price in dollars rather than as a vague sense that longer is more expensive.
| Term | Monthly payment | Total interest | Total paid |
|---|---|---|---|
| 3 years (36 months) | $591.43 | $3,291.48 | $21,291.48 |
| 4 years (48 months) | $467.41 | $4,435.68 | $22,435.68 |
| 5 years (60 months) | $393.61 | $5,616.60 | $23,616.60 |
| 6 years (72 months) | $344.92 | $6,834.24 | $24,834.24 |
Terms used on this page
- Amortization
- Amortization is the process of paying off a loan with equal, regular payments that each cover the interest due for the period plus a slice of principal. Early payments are mostly interest; later ones are mostly principal. By the final payment the balance reaches exactly zero, which is how most car, personal and student loans work.
- APR (Annual Percentage Rate)
- APR is the yearly cost of borrowing expressed as a single percentage that includes the interest rate plus certain required fees, such as origination charges. Because lenders must calculate it the same way under federal Truth in Lending rules, APR lets you compare loan offers on an even footing.
- Interest Rate
- An interest rate is the price of money, stated as a percentage of the balance per year. Borrowers pay it to lenders, and savers earn it from banks. The rate alone does not include fees or compounding, so it can understate the true yearly cost of a loan or overstate a simple comparison of savings accounts.
- Principal
- Principal is the amount of money you borrow, or the amount you deposit, before any interest. On a loan, it is the balance that interest is charged against, and each payment's non-interest portion reduces it. On savings, principal is your own money, the base on which interest is earned.
- Loan Term
- The loan term is the length of time you have to repay a loan, usually stated in months for consumer loans. A longer term lowers the monthly payment but increases the total interest you pay, because the balance stays outstanding longer. A shorter term costs more each month and less overall.
Loan Calculator: common questions
What information do I need to calculate a loan payment?
You need just three things: the amount you plan to borrow, the annual interest rate and the repayment term. With those, the calculator finds the fixed monthly payment for a standard installment loan. If your offer lists an origination fee, note whether it is taken out of your proceeds or added to the balance, because that changes what you actually borrow.
Does a lower monthly payment mean a cheaper loan?
No. A lower payment usually comes from a longer term, which keeps the balance alive for more months and adds interest. On $18,000 at 11.25%, a 6-year term cuts the payment to $344.92 but costs $6,834.24 in interest, versus $4,435.68 over 4 years. Compare total interest, not just the payment.
Why is most of my early payment going to interest?
Because interest is charged on the balance, and the balance is highest at the start. Each month the lender takes that month's interest first, and only the rest reduces principal. As the balance shrinks, the interest portion falls and principal takes a larger share, even though the payment stays the same.
Should I enter the APR or the interest rate?
Enter the interest rate, sometimes called the note rate, to get the payment. The APR includes certain fees spread over the term, so it is the better figure for comparing two offers but not for computing the monthly bill. Federal Truth in Lending rules require lenders to disclose both before you sign.
How much does a 1% rate difference change my payment?
On a mid-size personal loan the monthly change is modest, but it adds up over the term. For example, $18,000 over 4 years at 10.25% instead of 11.25% lowers the payment from $467.41 to $458.69, saving $418.56 in total. Run both rates in the calculator to see the exact gap for your loan.
Can I pay off a personal loan early?
Usually yes, and paying early reduces total interest because less balance is left to charge interest on. Check your loan agreement for a prepayment penalty, which would offset part of the saving. Also confirm with the lender that extra payments go to principal rather than being held for your next scheduled due date.
Does this calculator work for car or student loans?
It works for any fixed-rate loan repaid in equal monthly payments, so the core payment math is the same. Car loans involve trade-ins, taxes and down payments, and student loans have deferment and income-driven plans, so the dedicated calculators for those loans handle details this one leaves out. For a quick payment estimate, though, the results here will match.
What is the difference between total interest and total cost?
Total interest is only what you pay the lender for the use of the money. Total cost adds the principal back in, so it equals every payment added together. If you also paid upfront fees, your full cost of borrowing is higher than either figure shown here. The total cost of loan calculator adds those fees for you.
Why doesn't my lender's payment match the calculator?
Small gaps usually come from rounding, a first payment that covers more or fewer than 30 days of interest, or fees added to the balance. Large gaps often mean a different rate, a variable rate or added products such as credit insurance. Ask the lender for the amount financed and the exact rate used.
How do I lower the total interest on a loan?
Borrow less, choose a shorter term or get a lower rate. After closing, extra principal payments do the most good early, when the balance is highest. Even rounding a payment up each month trims interest, provided the loan has no prepayment penalty and the lender credits the extra to principal.
Sources
- Regulation Z (Truth in Lending), 12 CFR Part 1026 — Consumer Financial Protection Bureau. Accessed October 17, 2026.
- Consumer Credit – G.19 statistical release — Federal Reserve Board. Accessed October 17, 2026.
- Credit reports and scores — Consumer Financial Protection Bureau. Accessed October 17, 2026.
We cite primary sources: regulators, central-bank data and federal agencies. Worked examples on this page are our own calculations, last checked October 17, 2026. See our methodology.