Understanding how much mortgage you can afford is a crucial first step in the home-buying process. This calculator helps you estimate your potential borrowing capacity based on your income, debts, and desired down payment. Remember, this is an estimate, and your actual mortgage approval will depend on lender-specific criteria, credit score, and market conditions.
Your Estimated Mortgage Affordability
Maximum Monthly Payment:$0.00
Estimated Maximum Loan Amount:$0.00
Estimated Maximum Home Price:$0.00
function calculateMortgageAffordability() {
var grossIncome = parseFloat(document.getElementById("grossIncome").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 maxMonthlyPayment = 0;
var maxLoanAmount = 0;
var maxHomePrice = 0;
if (isNaN(grossIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) || grossIncome <= 0 || monthlyDebt < 0 || downPayment < 0 || interestRate <= 0 || loanTerm <= 0) {
document.getElementById("maxMonthlyPayment").textContent = "Invalid input. Please enter valid positive numbers.";
document.getElementById("maxLoanAmount").textContent = "";
document.getElementById("maxHomePrice").textContent = "";
return;
}
// General Rule of Thumb: Front-end ratio (housing costs) should not exceed 28% of gross monthly income.
// Back-end ratio (total debt including housing) should not exceed 36% of gross monthly income.
// We'll use the more conservative back-end ratio for this calculation to estimate maximum affordability.
var grossMonthlyIncome = grossIncome / 12;
var maxTotalDebtAllowed = grossMonthlyIncome * 0.36; // 36% back-end ratio
var maxMonthlyPayment = maxTotalDebtAllowed – monthlyDebt;
// Ensure maxMonthlyPayment is not negative
if (maxMonthlyPayment 0) {
// Mortgage Payment Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Where M is monthly payment, P is principal loan amount, i is monthly interest rate, n is number of payments
// Rearranging to solve for P: P = M [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var numerator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
maxLoanAmount = maxMonthlyPayment * (numerator / denominator);
} else {
// If interest rate is 0 (unlikely but for edge case)
maxLoanAmount = maxMonthlyPayment * numberOfPayments;
}
maxLoanAmount = Math.max(0, maxLoanAmount); // Ensure loan amount is not negative
maxHomePrice = maxLoanAmount + downPayment;
document.getElementById("maxMonthlyPayment").textContent = "$" + maxMonthlyPayment.toFixed(2);
document.getElementById("maxLoanAmount").textContent = "$" + maxLoanAmount.toFixed(2);
document.getElementById("maxHomePrice").textContent = "$" + maxHomePrice.toFixed(2);
}
.calculator-wrapper {
font-family: Arial, sans-serif;
max-width: 700px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
background-color: #f9f9f9;
}
.calculator-wrapper h1 {
text-align: center;
color: #333;
margin-bottom: 15px;
}
.calculator-wrapper p {
color: #555;
line-height: 1.6;
margin-bottom: 20px;
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 5px;
font-weight: bold;
color: #444;
}
.input-group input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1rem;
}
.calculator-wrapper button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-wrapper button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 30px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 5px;
text-align: center;
}
.calculator-result h2 {
color: #333;
margin-bottom: 15px;
}
.calculator-result p {
font-size: 1.1rem;
margin-bottom: 8px;
}
.calculator-result span {
font-weight: bold;
color: #007bff;
}