Calculating your car loan repayments is a crucial step before committing to a vehicle purchase. It helps you understand the ongoing financial commitment and ensures it fits comfortably within your budget. This calculator uses a standard loan amortization formula to provide an accurate estimate of your monthly payments.
How the Calculation Works
The formula used to calculate the monthly repayment (M) for a loan is based on the principal loan amount (P), the monthly interest rate (r), and the total number of payments (n).
M = P [ r(1 + r)^n ] / [ (1 + r)^n – 1]
Where:
M = Your total monthly loan repayment.
P = The principal loan amount. This is the car's price minus your down payment.
r = Your monthly interest rate. This is calculated by dividing your annual interest rate by 12 (e.g., 7.5% annual rate becomes 0.075 / 12 = 0.00625 monthly rate).
n = The total number of payments over the loan's lifetime. This is calculated by multiplying the loan term in years by 12 (e.g., a 5-year loan has 5 * 12 = 60 payments).
Key Factors Affecting Your Repayments
Car Price: A higher car price means a larger loan amount, leading to higher repayments.
Down Payment: A larger down payment reduces the principal loan amount, thus lowering your monthly payments.
Loan Term: A longer loan term spreads the cost over more payments, resulting in lower monthly payments but potentially higher total interest paid over time. A shorter term means higher monthly payments but less total interest.
Interest Rate (APR): This is one of the most significant factors. A higher annual percentage rate (APR) will substantially increase your monthly repayments and the total interest paid. Lenders determine this based on your creditworthiness.
Example Calculation
Let's consider an example:
Car Price: $30,000
Down Payment: $5,000
Loan Term: 5 years (60 months)
Annual Interest Rate: 7.5%
First, we calculate the principal loan amount (P):
$30,000 (Car Price) – $5,000 (Down Payment) = $25,000 (P)
Next, we calculate the monthly interest rate (r):
7.5% / 12 months = 0.075 / 12 = 0.00625 (r)
The total number of payments (n) is:
5 years * 12 months/year = 60 (n)
Calculating the components:
(1 + 0.00625)^60 ≈ 1.45329
M = 25000 [ 0.00625 * 1.45329 ] / [ 1.45329 – 1]
M = 25000 [ 0.009083 ] / [ 0.45329 ]
M = 25000 * 0.019994
M ≈ $499.85
So, the estimated monthly repayment for this car loan would be approximately $499.85. Use our calculator above to find your personalized repayment estimate!
function calculateRepayments() {
var carPrice = parseFloat(document.getElementById("carPrice").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var loanTermYears = parseFloat(document.getElementById("loanTerm").value);
var annualInterestRate = parseFloat(document.getElementById("interestRate").value);
var resultValueElement = document.getElementById("result-value");
// Input validation
if (isNaN(carPrice) || carPrice <= 0) {
resultValueElement.textContent = "Invalid Car Price";
return;
}
if (isNaN(downPayment) || downPayment < 0) {
resultValueElement.textContent = "Invalid Down Payment";
return;
}
if (isNaN(loanTermYears) || loanTermYears <= 0) {
resultValueElement.textContent = "Invalid Loan Term";
return;
}
if (isNaN(annualInterestRate) || annualInterestRate < 0) {
resultValueElement.textContent = "Invalid Interest Rate";
return;
}
var loanAmount = carPrice – downPayment;
if (loanAmount < 0) {
loanAmount = 0; // Cannot have negative loan amount
}
var monthlyInterestRate = annualInterestRate / 100 / 12;
var numberOfPayments = loanTermYears * 12;
var monthlyRepayment = 0;
if (loanAmount === 0) {
monthlyRepayment = 0;
} else if (monthlyInterestRate === 0) {
monthlyRepayment = loanAmount / numberOfPayments;
} else {
var numerator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
var denominator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
monthlyRepayment = loanAmount * (numerator / denominator);
}
// Format the result to two decimal places
resultValueElement.textContent = "$" + monthlyRepayment.toFixed(2);
}