Buying a home is a significant financial decision, and understanding how much you can realistically afford is crucial. This Mortgage Affordability Calculator helps you estimate the maximum mortgage loan you might qualify for based on common lending criteria. It's important to remember that this is an estimation, and your actual loan approval will depend on a lender's detailed review of your financial situation.
.calculator-container {
font-family: Arial, sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 20px;
}
.input-section {
display: grid;
grid-template-columns: repeat(2, 1fr);
gap: 15px;
margin-bottom: 20px;
}
.form-group {
display: flex;
flex-direction: column;
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.form-group label {
margin-bottom: 5px;
font-weight: bold;
color: #555;
}
.form-group input {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1em;
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button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1em;
cursor: pointer;
transition: background-color 0.3s ease;
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button:hover {
background-color: #0056b3;
}
.result-section {
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 5px;
text-align: center;
font-size: 1.1em;
color: #333;
min-height: 50px; /* To ensure it's visible even when empty */
}
.result-section strong {
color: #28a745;
}
function calculateAffordability() {
var annualIncome = parseFloat(document.getElementById("annualIncome").value);
var monthlyDebt = parseFloat(document.getElementById("monthlyDebt").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value) / 100; // Convert percentage to decimal
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(annualIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
annualIncome < 0 || monthlyDebt < 0 || downPayment < 0 || interestRate < 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Error: Please enter valid positive numbers for all fields.";
return;
}
// — Mortgage Affordability Calculation Logic —
// Common lending guidelines:
// 1. Front-end ratio (PITI / Gross Monthly Income) <= 28%
// 2. Back-end ratio (Total Monthly Debt / Gross Monthly Income) <= 36%
// We'll use the more conservative back-end ratio for this calculation to estimate maximum affordable debt.
// This calculator focuses on the maximum mortgage payment one might afford.
var grossMonthlyIncome = annualIncome / 12;
var maxAffordableTotalDebt = grossMonthlyIncome * 0.36; // 36% back-end ratio
var maxAffordableMortgagePayment = maxAffordableTotalDebt – monthlyDebt;
if (maxAffordableMortgagePayment < 0) {
resultDiv.innerHTML = "Based on your income and existing debts, you may not qualify for an additional mortgage payment.";
return;
}
// Now, we need to calculate the loan amount that results in this max affordable mortgage payment.
// The mortgage payment formula (M) is:
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Where:
// P = Principal loan amount
// i = monthly interest rate (annual rate / 12)
// n = total number of payments (loan term in years * 12)
// We need to rearrange the formula to solve for P (Principal loan amount):
// P = M [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var monthlyInterestRate = interestRate / 12;
var numberOfPayments = loanTerm * 12;
var maxLoanAmount = 0;
// Handle case where interest rate is 0
if (monthlyInterestRate === 0) {
maxLoanAmount = maxAffordableMortgagePayment * numberOfPayments;
} else {
var factor = Math.pow(1 + monthlyInterestRate, numberOfPayments);
maxLoanAmount = maxAffordableMortgagePayment * (factor – 1) / (monthlyInterestRate * factor);
}
// The calculated maxLoanAmount is the principal.
// The total house price one could afford would be the loan amount + down payment.
var maxHousePrice = maxLoanAmount + downPayment;
// Display the results
resultDiv.innerHTML =
"Estimated Maximum Mortgage Loan Amount: $" + maxLoanAmount.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ",") + "" +
"Estimated Maximum Affordable House Price (including down payment): $" + maxHousePrice.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ",") + "" +
"Note: This is an estimation based on a 36% debt-to-income ratio. Actual loan approval depends on lender underwriting.";
}