Méthodologie
How we calculate auto loan payments
Our methodology for the Calculatrice de Prêt Auto calculator: the formula, step-by-step calculation, authoritative sources, and limitations. Reviewed quarterly.
Formule
M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
Étape par étape
- 1
Determine the principal (P): the car price minus any down payment, trade-in, or rebates.
- 2
Get the APR from the lender (or estimate based on credit score: 6% excellent, 10% good, 18% fair).
- 3
Convert APR to monthly rate: r = APR / 12.
- 4
Determine the loan term: typically 36, 48, 60, 72, or 84 months.
- 5
Compute number of payments: n = term in months.
- 6
Apply the standard amortization formula for the monthly payment.
- 7
Calculate total interest: (monthly payment × n) − principal.
Sources autorisées
Every claim on this page is backed by an authoritative source.
Hypothèses
What we take to be true when applying this formula.
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Fixed APR. Dealer financing promotions may have a different rate than the standard offer.
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Simple interest (most auto loans use simple interest, not precomputed).
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Equal monthly payments.
Limites
What this method does NOT capture.
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Taxes, title, and registration fees are usually added to the financed amount and increase the actual payment.
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Extended warranties, GAP insurance, and add-ons are often rolled into the loan principal — read the contract.
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Cars depreciate. A long loan term (72–84 months) can put you "underwater" (owe more than the car is worth) for years.
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The "Rule of 20/4/10" suggests: 20% down, 4-year loan max, payment under 10% of gross income.
Dernière révision: 2026-06-15 • Reviewed by: CalcxApp editorial team