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Loan payments use the standard amortisation formula: M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1], where M is the monthly payment, P is the principal (loan amount), r is the monthly interest rate (annual rate ÷ 12 ÷ 100), and n is the total number of months. This produces a fixed monthly payment that reduces your balance to zero by the final payment.

A good rate depends on the loan type and your credit score. For car loans in 2025, competitive rates for borrowers with excellent credit (720+) are around 5–7%. Personal loan rates range from 7–12% for strong credit, rising to 20–36% for lower scores. Federal student loan rates for undergraduates are set at 6.53% for 2025–26. Always compare APR (not just the stated rate) to account for any fees.

A shorter term means higher monthly payments but substantially less total interest. For example, a $20,000 personal loan at 10%: over 36 months you pay $3,233 in interest; over 60 months you pay $5,496. You pay $2,263 more for the convenience of lower monthly payments. If you can comfortably afford the higher payment, a shorter term almost always costs less overall.

Extra payments reduce your outstanding principal directly, which lowers the balance on which interest accrues each month. This creates a compounding benefit — each extra dollar you pay today eliminates future interest charges. On a $30,000 car loan at 6.9% over 60 months, adding just $100/month extra saves approximately $700 in interest and pays it off 8 months early.

The interest rate is the cost of borrowing the principal only. APR (Annual Percentage Rate) includes the interest rate plus any fees — origination fees, closing costs, broker fees — expressed as a yearly rate. APR is always the correct number to compare across loan offers. A loan with a 9.9% rate and a 2% origination fee may have an APR of 10.8%, making it more expensive than a 10.2% rate loan with no fees.

With a subsidized federal loan, the government pays the interest that accrues during school and the 6-month grace period — so your balance doesn't grow. With an unsubsidized loan, interest accrues from the moment the loan is disbursed. If you don't pay it, the interest capitalizes (gets added to your principal), and you then pay interest on a larger balance for the entire repayment period. This can add thousands to your total repayment cost.

Paying off a loan early saves interest and improves your debt-to-income ratio. However, check your loan agreement for prepayment penalties — some lenders charge a fee for early payoff. Also weigh opportunity cost: if you have high-interest credit card debt, paying that down first saves more. If you have an emergency fund and no higher-rate debt, paying down your loan early is generally a sound financial move.

A car loan is secured — the vehicle is collateral, which means lower interest rates but the lender can repossess the car if you default. A personal loan is unsecured — no collateral, higher rates, but more flexible (use the funds for any purpose). Car loans typically factor in the vehicle price, down payment, trade-in value, sales tax, and dealer fees. Personal loans focus on the loan amount plus any origination or processing fees.