Loan Calculator
Monthly payment, total interest, and the full month-by-month amortization schedule for any fixed-rate loan — car, personal, or student. Add an optional extra payment to see how much time and interest it saves. Runs entirely in your browser.
Amortization schedule
| # | Payment | Principal | Interest | Balance |
|---|
What an amortized loan actually does
A fixed-rate loan charges interest on your remaining balance each month, and you pay a constant amount. Early on, the balance is large, so most of your payment is interest and only a little chips at principal. As the balance falls, the interest portion shrinks and more of each payment goes to principal. The amortization table makes this shift visible row by row — watch the "interest" column fall and the "principal" column rise.
Why the early payments feel like they go nowhere
On a 5-year, $25,000 loan at 7%, your first payment is roughly half interest. That's not a trick — it's just interest on a big balance. The practical consequence: the most powerful time to make an extra payment is early, when knocking down principal removes interest from the most remaining months. The same extra payment in the final year barely matters.
The extra-payment lever
Enter an extra monthly amount and the calculator re-runs the schedule. Because every extra dollar goes entirely to principal, it compounds in your favor: a smaller balance means less interest next month, which means more of the regular payment goes to principal, and so on. The result is a shorter term and lower total interest — both shown in the results.
The one-time extra payment works the same way for a lump sum. Pick the month it lands (a year-end bonus in month 12, say) and the schedule absorbs it there. The "interest saved" cell compares your plan — monthly extra, lump sum, or both — against paying the bare minimum, so you can see exactly what the extras buy you.
Related
- Personal finance hub — all our money calculators and guides
- Mortgage calculator — PITI + extra-principal payoff
- Debt payoff calculator — multiple debts, snowball vs avalanche
- Compound interest calculator — the same math, working for you
FAQ
Is anything I enter sent to a server?
No. The calculator runs entirely in your browser — open DevTools → Network and confirm. Your loan details never leave the tab, and the CSV is generated locally.
What's the difference between interest rate and APR?
The interest rate is the cost of borrowing the principal. APR also folds in certain fees, so it's usually slightly higher and is the better number for comparing offers. This calculator treats the rate you enter as the periodic rate applied to your balance — if your loan has big origination fees, enter the APR for a more honest total cost.
How is the monthly payment calculated?
The standard amortizing-loan (PMT) formula: M = P · r(1+r)ⁿ / ((1+r)ⁿ − 1), where P is the principal, r is the monthly rate (APR ÷ 12), and n is the number of monthly payments. It produces a fixed payment that pays the loan off exactly at the end of the term.
Does paying extra each month really help?
A lot, especially early. Every extra dollar goes straight to principal, which removes that dollar from every future interest calculation. Add an extra payment and the calculator shows how many months you shave off and how much interest you save. On a typical 5-year auto loan, even $50/month extra can cut several months and a few hundred dollars in interest.
What does the one-time extra payment do?
It models a lump sum — a bonus, tax refund, or windfall — applied to principal in a single month of your choosing. The calculator drops it into the schedule at that month and re-amortizes everything after it. Timing matters: a $2,000 lump in month 12 of a 5-year auto loan saves more interest than the same $2,000 in month 48, because it removes principal from more remaining months. You can combine it with a monthly extra; the "interest saved" figure counts both against a no-extras baseline.
What do the loan-type presets assume?
The Auto, Personal, and Student chips seed typical mid-2020s numbers — $35,000 at 6.5% over 5 years, $10,000 at 12% over 3 years, and $30,000 at 6% over 10 years — so you can start from a realistic baseline and then adjust. They're starting points, not quotes; your actual rate depends on credit, lender, and market.
Does this work for car, personal, and student loans?
Yes — any fixed-rate installment loan with a principal, rate, and term fits: auto, personal, student (standard repayment), or a generic fixed loan. For mortgages specifically, the mortgage calculator adds property tax, insurance, and PMI.
What about variable-rate or interest-only loans?
This tool assumes a fixed rate and full amortization (every payment includes principal). Variable-rate loans change the payment when the rate resets, and interest-only loans don't reduce principal during the interest-only period — neither is modelled here. Use it as a fixed-rate baseline.