Loan Calculator
Work out the monthly payment and total interest on any personal, auto, or fixed-term loan.
What this calculator does
Calculates the fixed monthly payment and total interest on a personal, auto, or other fixed-term loan, so you can see the real cost of borrowing before signing anything.
Who this is for
Anyone comparing loan offers from different lenders, checking whether a monthly payment fits their budget, or deciding between a shorter term with higher payments versus a longer term with lower payments but more total interest.
How this calculator works
Same amortization math as a mortgage, just typically over a shorter term. Every payment is the same amount, but the mix shifts over time — more interest early on, more principal later.
The formula
Monthly Payment = P × [r(1+r)n] ÷ [(1+r)n − 1], where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the number of monthly payments (term in months).
Worked example
A $15,000 loan at 9% APR over 48 months: monthly rate r = 0.09/12 = 0.0075. Payment = 15,000 × [0.0075(1.0075)48] ÷ [(1.0075)48 − 1] ≈ $373/month. Over 48 months that's $17,904 total, meaning roughly $2,904 in total interest on the $15,000 borrowed.
Principal vs. interest
Run the calculator above to see how much of your total repayment is interest.
Common mistakes
- Comparing loans by monthly payment alone. A longer term can lower your monthly payment while increasing total interest paid — always compare total cost, not just the monthly figure.
- Ignoring origination fees. Many personal and auto loans include an upfront fee that effectively raises your real APR above the advertised rate.
- Not checking for prepayment penalties. Some loans charge a fee for paying off early, which changes the math if you plan to pay it down faster than scheduled.
- Assuming a lower advertised rate always means a cheaper loan. Fees, term length, and whether interest is simple or compound can outweigh a small difference in the headline rate — compare total repayment amount, not rate alone.
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Frequently Asked Questions
Should I compare loans by monthly payment or total cost?
Total cost. A lower monthly payment often comes from a longer term, which usually means paying significantly more in total interest over the life of the loan.
Does this include fees?
No, this calculates payment based on the loan amount, rate, and term only. Origination fees or other upfront charges will raise your effective cost above what's shown here.
What happens if I pay extra each month?
Extra payments go directly toward principal, which reduces the balance interest is calculated on going forward — this can meaningfully cut total interest and shorten your payoff timeline, as long as your loan has no prepayment penalty.