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 your potential borrowing capacity based on your income, debts, and estimated interest rates. It's important to remember that this is an estimation, and lenders will perform their own detailed analysis.
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);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(annualIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
annualIncome <= 0 || monthlyDebt < 0 || downPayment < 0 || interestRate <= 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Lender typically allows PITI (Principal, Interest, Taxes, Insurance) to be around 28% of gross monthly income
var maxPITI_percentage = 0.28;
var grossMonthlyIncome = annualIncome / 12;
var maxPITI_payment = grossMonthlyIncome * maxPITI_percentage;
// Lenders also consider total debt ratio, typically around 36% of gross monthly income
var maxTotalDebt_percentage = 0.36;
var maxTotalDebt_payment = grossMonthlyIncome * maxTotalDebt_percentage;
var maxMortgagePayment = maxTotalDebt_payment – monthlyDebt;
// Use the lower of the two calculated maximum mortgage payments to be conservative
var maxAllowedMonthlyMortgage = Math.min(maxPITI_payment, maxMortgagePayment);
// — Mortgage Payment Calculation (for estimating loan amount) —
// 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
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
// To find P (principal), we rearrange the formula:
// P = M [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var principal = maxAllowedMonthlyMortgage * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
// The estimated maximum home price is the loan principal plus the down payment
var maxHomePrice = principal + downPayment;
resultDiv.innerHTML = "
Estimated Maximum Home Price: $" + maxHomePrice.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ",") + "";
resultDiv.innerHTML += "
This is an estimate. Actual loan amounts depend on lender underwriting, credit score, property taxes, homeowners insurance, and other factors.";
}
.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 h2 {
text-align: center;
margin-bottom: 20px;
color: #333;
}
.calculator-form .form-group {
margin-bottom: 15px;
}
.calculator-form label {
display: block;
margin-bottom: 5px;
font-weight: bold;
color: #555;
}
.calculator-form input[type="number"] {
width: calc(100% – 12px);
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
}
.calculator-container button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-container button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border-radius: 4px;
text-align: center;
font-size: 18px;
color: #333;
}
.calculator-result p {
margin: 5px 0;
}
.calculator-result em {
font-size: 14px;
color: #666;
}