Use this calculator to estimate how much house you can afford based on your income, debts, and down payment. Understanding your borrowing capacity is a crucial first step in the home-buying process.
function calculateMortgageAffordability() {
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
// Input validation
if (isNaN(annualIncome) || annualIncome <= 0 ||
isNaN(monthlyDebt) || monthlyDebt < 0 ||
isNaN(downPayment) || downPayment < 0 ||
isNaN(interestRate) || interestRate <= 0 ||
isNaN(loanTerm) || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Lender DTI (Debt-to-Income) ratios are typically around 28% for housing and 36%-45% for total debt.
// We'll use a common guideline: the maximum PITI (Principal, Interest, Taxes, Insurance) payment
// should not exceed 28% of gross monthly income. Total debt payments (including PITI)
// should not exceed 36% of gross monthly income.
var grossMonthlyIncome = annualIncome / 12;
// Max PITI allowed based on 28% rule
var maxPitiAllowed = grossMonthlyIncome * 0.28;
// Max Total Debt allowed based on 36% rule
var maxTotalDebtAllowed = grossMonthlyIncome * 0.36;
// Max allowed monthly mortgage payment (PITI) considering total debt
var maxMortgagePayment = maxTotalDebtAllowed – monthlyDebt;
// Ensure maxMortgagePayment is not negative
if (maxMortgagePayment 0 && numberOfPayments > 0) {
// Rearranging the formula 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);
if (denominator > 0) {
maxLoanAmount = maxPitiAllowed * (numerator / denominator);
}
}
// We need to consider the total debt constraint as well.
// The maximum monthly payment we can afford for PITI is maxTotalDebtAllowed – monthlyDebt.
// Let's recalculate maxLoanAmount using this potentially lower PITI value if it's more restrictive.
var pmtForMaxDebt = maxTotalDebtAllowed – monthlyDebt;
var maxLoanAmountFromTotalDebt = 0;
if (pmtForMaxDebt > 0 && monthlyInterestRate > 0 && numberOfPayments > 0) {
var numerator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
if (denominator > 0) {
maxLoanAmountFromTotalDebt = pmtForMaxDebt * (numerator / denominator);
}
}
// The actual maximum loan amount is the smaller of the two calculations.
// We also need to account for the down payment. The affordable home price is loan amount + down payment.
var affordableHomePrice = Math.min(maxLoanAmount, maxLoanAmountFromTotalDebt) + downPayment;
// Format the results
var formattedAffordableHomePrice = affordableHomePrice.toLocaleString(undefined, {
style: 'currency',
currency: 'USD'
});
var formattedMaxLoanAmount = Math.min(maxLoanAmount, maxLoanAmountFromTotalDebt).toLocaleString(undefined, {
style: 'currency',
currency: 'USD'
});
resultDiv.innerHTML = `
Estimated Affordability
Based on your inputs, the estimated maximum home price you can afford is: ${formattedAffordableHomePrice}
This includes your down payment of ${downPayment.toLocaleString(undefined, {style: 'currency', currency: 'USD'})}.
The estimated maximum loan amount you can qualify for is: ${formattedMaxLoanAmount}
Note: This is an estimate. Actual loan approval depends on lender guidelines, credit score, property taxes, insurance costs, and other factors.
`;
}
.calculator-container {
font-family: sans-serif;
border: 1px solid #ddd;
padding: 20px;
border-radius: 8px;
max-width: 600px;
margin: 20px auto;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 15px;
}
.calculator-container p {
text-align: center;
color: #555;
margin-bottom: 25px;
line-height: 1.6;
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
font-weight: bold;
margin-bottom: 5px;
color: #444;
}
.input-group input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1rem;
}
.calculator-container button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 1.1rem;
cursor: pointer;
transition: background-color 0.3s ease;
margin-top: 10px;
}
.calculator-container button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 4px;
text-align: center;
}
.calculator-result h3 {
margin-top: 0;
color: #333;
}
.calculator-result p {
margin-bottom: 10px;
color: #555;
font-size: 1.1rem;
}
.calculator-result strong {
color: #28a745; /* Green for emphasis on results */
}
.calculator-result small {
font-size: 0.85em;
color: #6c757d;
}