Understanding how much you can borrow is a crucial first step in the home-buying process. This mortgage affordability calculator helps you estimate your borrowing capacity based on your income and estimated monthly expenses. Remember, this is an estimate, and your actual loan offer may vary based on lender specifics, credit score, and a full financial assessment.
function calculateMortgageAffordability() {
var monthlyIncome = parseFloat(document.getElementById("monthlyIncome").value);
var existingDebts = parseFloat(document.getElementById("existingDebts").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value) / 100;
var loanTerm = parseInt(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("mortgageResult");
resultDiv.innerHTML = "; // Clear previous results
if (isNaN(monthlyIncome) || isNaN(existingDebts) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
monthlyIncome < 0 || existingDebts < 0 || downPayment < 0 || interestRate < 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Debt-to-Income Ratio (DTI) is a common metric lenders use.
// A common guideline is a maximum DTI of 43% (including proposed housing costs).
// We'll calculate maximum housing payment first.
var maxHousingPayment = (monthlyIncome * 0.43) – existingDebts;
if (maxHousingPayment 0) {
// Using the mortgage payment formula rearranged to solve for Principal (P)
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// P = M [ (1 + i)^n – 1] / [ i(1 + i)^n ]
maxLoanAmount = maxHousingPayment * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
} else {
// If interest rate is 0, loan amount is simply monthly payment * number of payments
maxLoanAmount = maxHousingPayment * numberOfPayments;
}
// The maximum loan amount we can borrow is 'maxLoanAmount'.
// The total home price we can afford is the max loan amount plus the down payment.
var maxAffordableHomePrice = maxLoanAmount + downPayment;
// Displaying the results
resultDiv.innerHTML = `
Estimated Maximum Monthly Housing Payment (Principal & Interest): $${maxHousingPayment.toFixed(2)}
Estimated Maximum Loan Amount You Could Borrow: $${maxLoanAmount.toFixed(2)}
Estimated Maximum Home Price You Can Afford: $${maxAffordableHomePrice.toFixed(2)}
Disclaimer: This is an estimate. Your actual affordability may differ based on lender policies, credit score, loan type, and specific property taxes and insurance costs.
`;
}
#mortgage-calculator {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}
#mortgage-calculator h2 {
text-align: center;
color: #333;
margin-bottom: 20px;
}
#mortgage-calculator p {
color: #555;
line-height: 1.6;
margin-bottom: 15px;
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 5px;
font-weight: bold;
color: #444;
}
.input-group input[type="number"],
.input-group input[type="text"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1rem;
}
#mortgage-calculator button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 10px;
}
#mortgage-calculator button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
background-color: #f9f9f9;
border: 1px solid #eee;
border-radius: 5px;
text-align: center;
}
.calculator-result p {
margin-bottom: 10px;
}
.calculator-result strong {
color: #333;
}
.calculator-result em {
font-size: 0.9em;
color: #777;
}