Loan Payment Calculator

Think of a loan payment like paying rent on borrowed money. Every month, you pay back a piece of what you borrowed plus rent on the remaining balance. Early payments are mostly rent (interest), while later payments are mostly principal.

The payment formula balances these two parts so your payment stays the same each month. As you pay down the principal, the interest portion shrinks and the principal portion grows. This is called amortization.

Lenders use compound interest, which means you pay interest on the remaining balance each month. A $25,000 loan at 6.5% doesn't just add $1,625 in interest per year - the interest compounds monthly on whatever balance remains.

Use this calculator when comparing loan offers or determining what you can afford before shopping. It's essential for auto loans, personal loans, and mortgages where you need fixed monthly payments.

Don't rely on it for credit cards, lines of credit, or variable-rate loans where payments change based on balance or market rates. Also avoid using it for loans with balloon payments, interest-only periods, or complex fee structures that alter the effective rate.

The calculator works best for standard amortizing loans with fixed rates and equal monthly payments. If your loan has unusual terms, prepayment penalties, or rate adjustments, you need specialized calculators or lender-provided payment schedules.

The biggest mistake is focusing only on monthly payment without considering total cost. A longer loan term reduces your monthly payment but can double your total interest. A $20,000 car loan at 7% costs $2,750 in interest over 4 years but $5,800 over 8 years.

Another error is ignoring additional costs beyond principal and interest. Car loans may require full coverage insurance. Mortgages include property taxes, homeowners insurance, and possibly PMI. Personal loans might have origination fees that effectively raise your interest rate.

Many borrowers also underestimate how credit score affects rates. The difference between excellent and fair credit can mean 3-5% higher rates, adding thousands to total cost on larger loans.

Monthly payment calculation uses the present value of annuity formula: PMT = P × [r(1+r)^n] / [(1+r)^n - 1], where P is principal, r is monthly interest rate, and n is number of payments.

The monthly rate converts annual percentage rate: if your loan has 6% APR, the monthly rate is 0.06/12 = 0.005. For a 5-year loan, n equals 60 payments. This formula ensures your payment covers both interest on the remaining balance and principal reduction.

Zero-interest loans simplify to P/n since there's no compound growth. The formula breaks down at very high rates or long terms where payments might not cover monthly interest, creating negative amortization.

Loan payments front-load interest because interest accrues on the full remaining balance. Making extra principal payments early in the loan term saves disproportionate interest over time. Even an extra $50 monthly on a $300,000 mortgage can save $50,000+ in interest.