Mortgage Affordability Calculator
Understanding how much house you can afford is a crucial first step in the home-buying process. This Mortgage Affordability Calculator helps you estimate the maximum loan amount you might qualify for based on your income, debts, and desired loan terms. It's important to remember that this is an estimation tool, and your actual loan approval will depend on a lender's thorough review of your financial situation, credit score, and other factors.
function calculateAffordability() {
var monthlyIncome = parseFloat(document.getElementById("monthlyIncome").value);
var monthlyDebtPayments = parseFloat(document.getElementById("monthlyDebtPayments").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(monthlyIncome) || isNaN(monthlyDebtPayments) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (monthlyIncome <= 0 || monthlyDebtPayments < 0 || downPayment < 0 || interestRate <= 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter positive values for income, interest rate, and loan term, and non-negative values for debts and down payment.";
return;
}
// Debt-to-Income Ratio (DTI) commonly used by lenders (e.g., 43%)
// This is a simplified model. Lenders use complex DTI calculations.
var maxMonthlyHousingPayment = (monthlyIncome * 0.43) – monthlyDebtPayments;
if (maxMonthlyHousingPayment <= 0) {
resultDiv.innerHTML = "Based on your income and existing debts, it may be difficult to qualify for a new mortgage at this time. Consider reducing debt or increasing income.";
return;
}
// Calculate maximum loan amount using the loan payment formula
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Where:
// M = monthly payment
// P = principal loan amount
// i = monthly interest rate
// n = total number of payments (loan term in years * 12)
var annualInterestRateDecimal = interestRate / 100;
var monthlyInterestRate = annualInterestRateDecimal / 12;
var numberOfPayments = loanTerm * 12;
// Rearrange formula to solve for P (Principal Loan Amount)
// P = M [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var principal = maxMonthlyHousingPayment * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
// Affordability is the maximum loan amount plus the down payment
var maxHomePrice = principal + downPayment;
// Display results with formatting
resultDiv.innerHTML = `
Your Estimated Affordability
Maximum Monthly Housing Payment You Can Afford (P&I): $${maxMonthlyHousingPayment.toFixed(2)}
Estimated Maximum Loan Amount: $${principal.toFixed(2)}
Estimated Maximum Home Purchase Price: $${maxHomePrice.toFixed(2)}
Note: This is an estimate. Actual loan approval depends on lender's criteria, credit score, property taxes, homeowners insurance, and PMI (if applicable).
`;
}
.calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}
.calculator-container h1 {
text-align: center;
color: #333;
margin-bottom: 15px;
}
.calculator-container p {
color: #555;
line-height: 1.6;
margin-bottom: 20px;
}
.calculator-form {
display: grid;
grid-template-columns: 1fr;
gap: 15px;
}
.form-group {
display: flex;
flex-direction: column;
}
.form-group label {
margin-bottom: 8px;
font-weight: bold;
color: #444;
}
.form-group input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
}
.calculator-form button {
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 16px;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 10px;
}
.calculator-form button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
border-top: 1px solid #eee;
}
.calculator-result h3 {
color: #333;
margin-bottom: 10px;
}
.calculator-result p {
margin-bottom: 8px;
color: #333;
}
.calculator-result p strong {
color: #007bff;
}