Mortgage Affordability Calculator
Use this calculator to estimate how much you can afford to borrow for a mortgage based on your income, debts, and down payment.
.calculator-container {
font-family: sans-serif;
max-width: 500px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ccc;
border-radius: 8px;
box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}
.calculator-container h2 {
text-align: center;
margin-bottom: 15px;
color: #333;
}
.calculator-container p {
text-align: center;
color: #555;
margin-bottom: 25px;
font-size: 0.9em;
}
.input-section {
display: grid;
grid-template-columns: 1fr;
gap: 15px;
}
.input-section label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #444;
}
.input-section input[type="number"] {
width: 100%;
padding: 10px;
border: 1px solid #ddd;
border-radius: 4px;
box-sizing: border-box; /* Include padding and border in the element's total width and height */
}
.input-section button {
background-color: #4CAF50;
color: white;
padding: 12px 20px;
border: none;
border-radius: 4px;
cursor: pointer;
font-size: 16px;
transition: background-color 0.3s ease;
}
.input-section button:hover {
background-color: #45a049;
}
#result {
margin-top: 25px;
padding: 15px;
background-color: #e9f7ef;
border: 1px solid #d0e9c6;
border-radius: 4px;
text-align: center;
font-size: 1.1em;
color: #3c763d;
font-weight: bold;
}
#result:empty {
display: none; /* Hide if empty */
}
var calculateMortgageAffordability = function() {
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;
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.textContent = ""; // Clear previous results
// Basic validation
if (isNaN(annualIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm)) {
resultDiv.textContent = "Please enter valid numbers for all fields.";
return;
}
if (annualIncome <= 0 || monthlyDebt < 0 || downPayment < 0 || interestRate < 0 || loanTerm <= 0) {
resultDiv.textContent = "Please enter positive values where appropriate.";
return;
}
// Lender's common debt-to-income ratio guidelines (often 28%/36%)
// Front-end ratio (housing costs): Max 28% of gross monthly income
// Back-end ratio (total debt): Max 36% of gross monthly income
var grossMonthlyIncome = annualIncome / 12;
// Estimate maximum affordable monthly payment (PITI – Principal, Interest, Taxes, Insurance)
// We'll use the back-end ratio as a primary constraint, as it includes all debts.
// Lenders vary, but 36% is a common benchmark for total debt payments.
var maxTotalMonthlyPayments = grossMonthlyIncome * 0.36;
// Deduct existing monthly debt payments to find the maximum affordable P&I payment
var maxMortgagePayment = maxTotalMonthlyPayments – monthlyDebt;
if (maxMortgagePayment 0) {
var powInterestRate = Math.pow(1 + monthlyInterestRate, numberOfPayments);
maxLoanAmount = maxMortgagePayment * (powInterestRate – 1) / (monthlyInterestRate * powInterestRate);
} else { // Handle 0% interest rate case (though rare for mortgages)
maxLoanAmount = maxMortgagePayment * numberOfPayments;
}
// The maxLoanAmount calculated is what you can borrow based on P&I only.
// To estimate the maximum home price, we add the down payment.
var estimatedMaxHomePrice = maxLoanAmount + downPayment;
// Format results
var formattedMaxLoanAmount = maxLoanAmount.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 });
var formattedEstimatedMaxHomePrice = estimatedMaxHomePrice.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 });
var formattedMaxMortgagePayment = maxMortgagePayment.toLocaleString(undefined, { minimumFractionDigits: 0, maximumFractionDigits: 0 });
resultDiv.innerHTML =
"
Estimated Maximum Loan Amount: $" + formattedMaxLoanAmount + "" +
"
Estimated Maximum Home Price: $" + formattedEstimatedMaxHomePrice + "" +
"
(Based on a maximum P&I payment of $" + formattedMaxMortgagePayment + " per month and your inputs. This excludes property taxes, homeowners insurance, and HOA fees.)";
};