What is a loan calculator?
A loan calculator answers the one question every borrower actually has: how much will this cost me each month, and how much will it cost me total? Three numbers in (loan amount, interest rate, term), three numbers out (monthly payment, total interest, total paid). That's it.
The math has been the same since the late 1800s — it's the standard amortization formula every bank in the world uses to set up a fixed-payment loan. What changes is the inputs, and that's where you have all the power. Borrow $15,000 over five years instead of three? Different payment, different total cost. Take 8% APR instead of 6%? Same loan, hundreds of dollars more in interest. Most loan decisions get made in a car dealership or mortgage office in 90 seconds. This Loan Calculator lets you actually think about them.
The version on this page handles any fixed-rate, fixed-term, fully-amortizing loan: car loans, personal loans, student loans, mortgages, anything where you pay the same amount every month until it's gone. No fine print, no sign-up, no "calculate now to see if you qualify." Just the math.
How to use the Loan Calculator
Three inputs. Results update as you type.
- Enter the loan amount in dollars (the amount you're borrowing, after any down payment)
- Enter the annual interest rate (APR) as a percentage
- Enter the loan term in years (3, 5, 7, 30 — whatever the lender is offering)
You'll see three numbers come back: your fixed monthly payment, the total interest you'll pay over the full term, and the grand total (principal plus interest). The numbers stay in your browser. No data leaves the page.
The formula behind a fixed-payment loan
The standard amortization formula looks intimidating but it's the same math your lender uses:
M = P × [r(1+r)n] / [(1+r)n − 1]
Where:
- M = monthly payment
- P = principal (the amount borrowed)
- r = monthly interest rate (annual rate ÷ 12, as a decimal)
- n = total number of monthly payments (years × 12)
Each month, part of your payment covers interest on the current balance and part chips away at the principal. In month one, most of the payment is interest — the balance is still huge. In month 60 (or month 360, for a 30-year mortgage), almost the entire payment is going to principal. The proportions shift gradually. This is called the amortization schedule, and you can see it visualized in the Amortization Calculator.
Worked example: $15,000 at 8% for 4 years
You're buying a used car and the dealership offers $15,000 financed at 8% APR over 48 months. Let's see what that actually costs.
First the inputs converted to the formula's units:
- P = $15,000
- r = 0.08 ÷ 12 = 0.006667
- n = 4 × 12 = 48
Plug it in:
M = 15,000 × [0.006667 × (1.006667)48] / [(1.006667)48 − 1] = $366.19/month
So you'll pay $366.19 every month for four years. Total paid: 366.19 × 48 = $17,577.12. Total interest: $2,577.12.
The car cost you $15,000. The financing cost you another $2,577. Whether that's a good deal depends on what else you'd have done with that money (an investment earning 8% would have made it back, but most people don't actually run that comparison — they just sign).
How term and rate change the deal
The table below shows what happens to the same $15,000 loan at three different rates across three different terms. Read across to see the rate impact; read down to see the term impact.
| Term | 6% APR | 8% APR | 10% APR |
|---|---|---|---|
| 3 years (36 mo) | $456.33 — total $16,427 — interest $1,427 | $470.05 — total $16,922 — interest $1,922 | $484.01 — total $17,424 — interest $2,424 |
| 5 years (60 mo) | $289.99 — total $17,400 — interest $2,400 | $304.15 — total $18,249 — interest $3,249 | $318.71 — total $19,123 — interest $4,123 |
| 7 years (84 mo) | $219.13 — total $18,407 — interest $3,407 | $233.81 — total $19,640 — interest $4,640 | $249.05 — total $20,920 — interest $5,920 |
Two patterns to notice:
Longer term = lower monthly payment but dramatically more interest. The 7-year loan at 8% costs $4,640 in interest. The 3-year loan at the same rate costs only $1,922. Stretching the term cut the monthly payment from $470 to $234, but you pay $2,718 extra for that flexibility. That's the cost of giving yourself time.
Rate matters more on longer terms. On the 3-year loan, going from 6% to 10% adds $997 in total interest. On the 7-year loan, the same 4-point rate jump adds $2,513. The longer the money is outstanding, the more the interest rate gets to chew on it.
This is why credit unions, online lenders, and rate-shopping all matter. Half a percentage point off your rate on a mortgage saves tens of thousands of dollars across 30 years. The same half-point on a 3-year car loan saves you a tank of gas. Hunt for the rate where the dollar impact is biggest — that's the 30-year mortgage, not the 36-month car loan.
What's typical for each loan type
Knowing the going rate for your loan type is half the battle. These are typical APR ranges in the U.S. as of 2025:
| Loan type | Typical APR range | Typical term |
|---|---|---|
| 30-year fixed mortgage | 6.5% – 7.5% | 30 years |
| 15-year fixed mortgage | 5.8% – 6.8% | 15 years |
| Auto loan (new car) | 5% – 8% | 3 – 7 years |
| Auto loan (used car) | 7% – 11% | 3 – 6 years |
| Federal student loan (undergrad) | 5% – 7% | 10 years standard |
| Personal loan (good credit) | 8% – 15% | 2 – 7 years |
| Personal loan (fair credit) | 15% – 25% | 2 – 5 years |
| Credit card | 18% – 28% | Revolving (no fixed term) |
If a lender quotes you a rate noticeably above the range for your loan type, shop around. Most of the rate spread within a category is about credit score, but some of it is just lender margin. Three quotes typically reveals which one is which.
Should you pay off the loan early?
Almost always yes, if you can afford it. The interest savings from prepaying are immediate and guaranteed. On the $15,000 / 8% / 4-year example above, paying it off one year early (sending $366.19 × 12 = $4,394 in extra payments spread across the loan) saves about $560 in interest. Doing the same on a 30-year mortgage can save tens of thousands.
The catch: some loans have prepayment penalties. Most modern consumer loans don't, but a few do — check your loan agreement before sending extra money. If the loan is penalty-free, every extra dollar toward principal is a dollar you don't pay interest on for the rest of the loan's life. The Mortgage Payoff Calculator is the version of this for home loans specifically, where the dollar amounts get large enough to matter most.
The opposite case: if your loan rate is unusually low (like a 3% mortgage from 2021), prepaying might be worse than investing the same money. A diversified portfolio averages 7% to 10% over long timeframes; if you can earn more on the cash than you save in interest, the math says don't prepay. The Compound Interest Calculator on the related page lets you run that comparison.
Related calculations
- Payment Calculator — a more flexible version that can solve for any of the four variables (payment, principal, rate, or term) when you know the other three.
- Amortization Calculator — shows the full month-by-month breakdown of principal vs. interest, plus running balance. Useful for understanding where your money actually goes early in the loan.
- Compound Interest Calculator — the same math from the lender's perspective. If you've ever wondered how the bank can afford to lend at 6%, this is why.
Frequently asked questions
What's the difference between APR and interest rate?
The interest rate is the cost of borrowing the principal. APR (annual percentage rate) is the interest rate plus other required loan costs — origination fees, points, mortgage insurance, etc. — expressed as an annualized percentage. APR is always equal to or higher than the interest rate. For comparison shopping, always use APR — that's the true cost. The Loan Calculator above treats the input as APR; if you only know the interest rate, the result will be slightly understated.
Why is my first few payments mostly interest?
Because interest is calculated on the remaining balance, which is largest at the start. On a 30-year mortgage at 7%, the first month's payment is roughly 80% interest and 20% principal. By month 200, it's about 50/50. By the final year, almost all of each payment is principal. This is the amortization schedule doing its thing — exactly what it's mathematically supposed to do, even when it feels unfair.
Does the Loan Calculator account for taxes and insurance?
No. It calculates only the principal and interest payment (often abbreviated "P&I"). For a mortgage, your actual monthly payment usually also includes property taxes, homeowners insurance, and possibly mortgage insurance — together called PITI. Those vary by location and lender, so they aren't included. Budget an extra 20% to 30% on top of the P&I number for a rough mortgage total. Other loan types (auto, personal, student) don't usually have additional escrow components, so the P&I number is the full payment.
Can I use this for a balloon loan or interest-only loan?
No — the calculator assumes a fully amortizing loan where every payment is the same and the balance reaches zero at the end. Balloon loans (one large final payment) and interest-only loans (no principal paid until the end) use different math. Most consumer loans are fully amortizing; balloon and interest-only structures are mostly used in commercial real estate and certain mortgage products.
How do I know if I'm getting a good rate?
Shop three lenders for any loan above $5,000. For mortgages and auto loans, also check a credit union — they often beat banks on rate. For personal loans, online lenders like SoFi, LightStream, and Marcus typically beat traditional banks on rate (though they require good credit). Your credit score is the biggest single factor; pull your score before you shop so you know where you stand and what rates you should expect.
What happens if I miss a payment?
Most lenders give a grace period (usually 10 to 15 days) before assessing a late fee. The late payment gets reported to credit bureaus after 30 days, which can drop your credit score 60 to 100 points. Two missed payments and the loan goes "delinquent"; three and it heads toward default and possible collection. If you're going to miss a payment, call the lender first — most have hardship programs that beat the credit hit of just not paying.
Should I always choose the shortest loan term I can afford?
Usually but not always. Shorter terms save interest but create a bigger monthly commitment, leaving less cushion if your income drops or an emergency hits. The general rule: choose the shortest term whose payment leaves you with at least three months of expenses in savings as a buffer. Stretching to the longest term to lower the payment is a sign you can't really afford the loan — at which point the right move is usually to borrow less, not stretch longer.
Can I refinance to get a better rate later?
Yes, for mortgages and some auto loans. Refinancing replaces the existing loan with a new one at a different rate or term. It typically makes sense when rates have dropped at least 0.75 to 1 percentage point below your current rate and you plan to keep the loan long enough to recoup the closing costs (often 2% to 3% of the loan amount for a mortgage). For credit cards, the equivalent move is a balance transfer to a 0% APR offer — same idea, different mechanism.