Mortgage Affordability Calculator
Understanding how much you can afford for a mortgage is a crucial first step in the home-buying process. This calculator helps you estimate your maximum affordable mortgage payment based on your income, debts, and estimated homeownership costs. It takes into account common ratios lenders use to determine affordability.
.calculator-container {
font-family: 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;
margin-bottom: 20px;
color: #333;
}
.calculator-container p {
margin-bottom: 20px;
color: #555;
line-height: 1.5;
}
.calculator-form .form-group {
margin-bottom: 15px;
}
.calculator-form label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #444;
}
.calculator-form input[type="number"] {
width: calc(100% – 22px);
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
box-sizing: border-box;
}
.calculator-form button {
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 16px;
transition: background-color 0.3s ease;
}
.calculator-form button:hover {
background-color: #0056b3;
}
#result {
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 4px;
text-align: center;
font-size: 1.1em;
color: #333;
}
#result p {
margin: 5px 0;
}
function calculateMortgageAffordability() {
var annualIncome = parseFloat(document.getElementById("annualIncome").value);
var monthlyDebtPayments = parseFloat(document.getElementById("monthlyDebtPayments").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var estimatedMonthlyTaxes = parseFloat(document.getElementById("estimatedMonthlyTaxes").value);
var estimatedMonthlyInsurance = parseFloat(document.getElementById("estimatedMonthlyInsurance").value);
var estimatedMonthlyHOA = parseFloat(document.getElementById("estimatedMonthlyHOA").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
// Basic validation
if (isNaN(annualIncome) || annualIncome <= 0 ||
isNaN(monthlyDebtPayments) || monthlyDebtPayments < 0 ||
isNaN(downPayment) || downPayment < 0 ||
isNaN(estimatedMonthlyTaxes) || estimatedMonthlyTaxes < 0 ||
isNaN(estimatedMonthlyInsurance) || estimatedMonthlyInsurance < 0 ||
isNaN(estimatedMonthlyHOA) || estimatedMonthlyHOA < 0 ||
isNaN(interestRate) || interestRate <= 0 ||
isNaN(loanTerm) || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// LTV calculation is not directly used to determine maximum affordable payment,
// but it's good to keep in mind for loan approval.
// This calculator focuses on the Debt-to-Income (DTI) ratios.
// Common DTI ratios used by lenders:
// Front-end ratio (Housing Ratio): PITI / Gross Monthly Income (typically < 28-31%)
// Back-end ratio (Total Debt Ratio): (PITI + Other Debts) / Gross Monthly Income (typically < 36-43%)
var grossMonthlyIncome = annualIncome / 12;
// — Calculate Maximum Affordable PITI based on Back-End Ratio —
// We'll use a conservative back-end ratio limit (e.g., 43%) for maximum affordability.
var maxTotalDebtPayment = grossMonthlyIncome * 0.43; // Max PITI + Monthly Debt
var maxPITI = maxTotalDebtPayment – monthlyDebtPayments;
// Ensure maxPITI is not negative
if (maxPITI 0 && monthlyInterestRate > 0 && numberOfPayments > 0) {
var numerator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
maxLoanAmount = maxPrincipalAndInterest * (numerator / denominator);
} else if (maxPITI >= nonPrincipalCosts) {
// If maxPITI covers all other costs, it means we could potentially afford a small loan or $0 loan
// if the non-principal costs are very high. For simplicity, we'll set maxLoanAmount to 0
// if maxPrincipalAndInterest is not positive.
maxLoanAmount = 0;
} else {
// If maxPITI is less than non-principal costs, it means affordability is too low for this scenario.
maxLoanAmount = 0;
}
// Calculate maximum affordable home price
var affordableHomePrice = maxLoanAmount + downPayment;
// Calculate the estimated monthly mortgage payment for the calculated maxLoanAmount
var estimatedMonthlyMortgagePayment = 0;
if (maxPrincipalAndInterest > 0 && monthlyInterestRate > 0 && numberOfPayments > 0) {
var numerator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
var denominator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
estimatedMonthlyMortgagePayment = maxLoanAmount * (numerator / denominator);
} else {
estimatedMonthlyMortgagePayment = 0;
}
var finalPITI = estimatedMonthlyMortgagePayment + estimatedMonthlyTaxes + estimatedMonthlyInsurance + estimatedMonthlyHOA;
// Calculate final DTI ratios for context
var frontEndRatio = (finalPITI / grossMonthlyIncome) * 100;
var backEndRatio = ((finalPITI + monthlyDebtPayments) / grossMonthlyIncome) * 100;
// Display results
resultDiv.innerHTML += "
Your Estimated Affordability:
";
resultDiv.innerHTML += "Maximum Affordable Home Price:
$" + affordableHomePrice.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 }) + "";
resultDiv.innerHTML += "Estimated Maximum Loan Amount:
$" + maxLoanAmount.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 }) + "";
resultDiv.innerHTML += "Estimated Maximum Total Monthly Housing Payment (PITI + HOA):
$" + finalPITI.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 }) + "";
resultDiv.innerHTML += "Based on a
" + (frontEndRatio.toFixed(1)) + "% front-end ratio and a
" + (backEndRatio.toFixed(1)) + "% back-end ratio.";
resultDiv.innerHTML += "
Note: This is an estimate. Actual loan approval depends on lender policies, credit score, employment history, and other factors.";
}