Practical guide

How to Calculate Loan Payments

Understand monthly payment math with an easy formula breakdown.

Quick Answer

Monthly loan payment uses the amortization formula: M = P × [r(1+r)^n] / [(1+r)^n − 1], where P is principal, r is monthly rate, and n is number of months.

Step-by-Step Method

Convert the annual interest rate to a monthly decimal rate (APR ÷ 12 ÷ 100).
Set n to the total number of monthly payments (years × 12).
Plug P, r, and n into the amortization formula or use the loan payment calculator.
Review total interest paid over the full term before signing.

Worked Example

A $20,000 loan at 7% APR for 5 years (60 months): monthly rate = 0.07/12 ≈ 0.00583. Payment ≈ $396/month. Total repaid ≈ $23,760.

Detailed Explanation

The payment on a standard amortising loan stays fixed, but its composition shifts month by month. Early payments are mostly interest, because interest is charged on a balance that has barely moved; later payments are mostly principal. On a five-year loan the crossover comes reasonably early, but on a long-term loan the first years contribute strikingly little to what you actually owe. This is why paying off a loan two years in often reveals a balance far higher than expected.

Term length is the lever most borrowers underweight. Extending a loan lowers the monthly payment, which is the number people shop on, while raising total interest — sometimes substantially, because you are borrowing the same money for longer. Running a three-year against a five-year scenario on the same principal and rate shows the trade-off in currency rather than in abstract. The right answer depends on whether the constraint is monthly cash flow or total cost, and it is worth deciding which before looking at offers.

The headline rate is not the whole price. Origination fees, mandatory insurance add-ons, and administrative charges raise the effective cost above the nominal rate, which is precisely what APR exists to capture — so compare APR to APR, never APR to nominal. Check separately whether the loan permits extra payments toward principal without penalty. Where it does, even modest additional payments made early cut total interest disproportionately, because they remove principal during the period when interest is accruing on the largest balance.

Use the Calculator

Run your real values in the interactive tool and review assumptions before taking action.

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FAQ

What is the difference between APR and interest rate?

APR includes certain fees and reflects the yearly cost more completely. The nominal rate may be lower than APR.

How does a larger down payment affect payments?

A larger down payment reduces principal (P), which lowers both monthly payment and total interest.

Should I choose the longest term for lower payments?

Longer terms reduce monthly payment but increase total interest. Balance affordability with total cost.