What the Car APR Calculator Does
The Car APR Calculator turns three simple numbers — your loan amount, loan term and annual percentage rate (APR) — into a clear picture of what an auto loan really costs. Instead of guessing, you instantly see your fixed monthly payment, the total interest you'll pay over the life of the loan, and the overall amount repaid. It's ideal for comparing dealer financing offers, bank loans and credit union deals side by side before you sign anything.
The Three Inputs Explained
- Loan Amount ($): The principal you're borrowing — the vehicle price minus any down payment or trade-in value.
- Loan Term (months): How long you'll repay, entered in months (e.g. 60 for a 5-year loan).
- Annual Percentage Rate (APR %): The yearly interest rate quoted on the loan, such as 6.5.
The Formula Behind It
The calculator uses the standard amortising loan payment formula. First it converts your APR into a monthly rate:
- Monthly rate \(r = \text{APR} \div 12 \div 100\)
- \(\text{Monthly Payment} = P \times r \times (1 + r)^{n} \div ((1 + r)^{n} - 1)\), where P is the loan amount and n is the term in months.
- \(\text{Total Payment} = \text{Monthly Payment} \times n\)
- \(\text{Total Interest} = \text{Total Payment} - \text{Loan Amount}\)
$$ M = P \cdot \frac{r\,(1+r)^{n}}{(1+r)^{n}-1} $$
$$ \text{where}\quad \left\{ \begin{aligned} P &= \text{Loan Amount} \\ r &= \dfrac{\text{APR}}{1200} \\ n &= \text{Term (months)} \end{aligned} \right. $$
Worked Example
Suppose you borrow $25,000 over 60 months at an 6.5% APR.
- Monthly rate \(= 6.5 \div 12 \div 100 = 0.005417\)
- Monthly payment \(\approx\) $489.15
- Total payment \(= \$489.15 \times 60 \approx\) $29,349
- Total interest \(= \$29{,}349 - \$25{,}000 \approx\) $4,349
So that $25,000 car actually costs around $29,349 once interest is included.
Frequently Asked Questions
Does a longer term lower my payment? Yes — stretching the same loan over more months reduces each monthly payment, but it increases the total interest because you're borrowing for longer.
Is APR the same as the interest rate? They're closely related here. This calculator treats your entered APR as the annual interest rate applied monthly. Real-world APR may also fold in certain fees, so always check what your lender includes.
What if I enter 0% APR? With a true 0% promotional rate, your monthly payment is simply the loan amount divided by the term, and total interest is zero.
