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 mortgage amount based on your income, debts, and desired monthly payment. It considers common lending ratios and a hypothetical interest rate to give you a ballpark figure. Remember, this is an estimate and actual loan approval will depend on lender-specific criteria, your credit score, down payment, and other factors.
Your Estimated Maximum Mortgage Affordability:
.calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
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.input-section input[type="number"] {
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.calculator-container button:hover {
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.result-section {
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padding: 15px;
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#notes {
font-size: 14px;
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color: #6c757d;
margin-top: 10px;
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function calculateMortgageAffordability() {
var monthlyIncome = parseFloat(document.getElementById("monthlyIncome").value);
var existingMonthlyDebt = parseFloat(document.getElementById("existingMonthlyDebt").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var desiredMonthlyPayment = parseFloat(document.getElementById("desiredMonthlyPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var maxMortgageAmountElement = document.getElementById("maxMortgageAmount");
var notesElement = document.getElementById("notes");
// Clear previous results
maxMortgageAmountElement.textContent = "";
notesElement.textContent = "";
// Basic validation
if (isNaN(monthlyIncome) || isNaN(existingMonthlyDebt) || isNaN(downPayment) || isNaN(desiredMonthlyPayment) || isNaN(interestRate) || isNaN(loanTermYears) ||
monthlyIncome < 0 || existingMonthlyDebt < 0 || downPayment < 0 || desiredMonthlyPayment < 0 || interestRate < 0 || loanTermYears maxPIMayExceedIncomeLimit) {
notesElement.textContent = "Your desired monthly payment might be too high based on the 28% of income rule. Consider reducing it or increasing income.";
notesElement.style.color = "#ffc107"; // Warning yellow
}
// Another common metric is the debt-to-income ratio (DTI), where total debt (including mortgage PITI) should not exceed 43% of gross income.
// Since we only have P&I, we can't fully calculate DTI without taxes and insurance.
// However, we can estimate the maximum affordable loan principal using the desired monthly P&I payment.
// Formula for monthly payment: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Where:
// M = Monthly Payment (desiredMonthlyPayment)
// P = Principal Loan Amount (what we want to find)
// i = monthly interest rate (annual interest rate / 12 / 100)
// n = total number of payments (loan term in years * 12)
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTermYears * 12;
var maxLoanPrincipal = 0;
// Avoid division by zero if monthlyInterestRate is 0 (though unlikely for mortgage rates)
if (monthlyInterestRate > 0 && numberOfPayments > 0) {
var numerator = monthlyInterestRate * Math.pow((1 + monthlyInterestRate), numberOfPayments);
var denominator = Math.pow((1 + monthlyInterestRate), numberOfPayments) – 1;
var loanFactor = numerator / denominator;
if (loanFactor > 0) {
maxLoanPrincipal = desiredMonthlyPayment / loanFactor;
}
} else if (numberOfPayments > 0) { // Handle 0% interest rate scenario, though very rare
maxLoanPrincipal = desiredMonthlyPayment * numberOfPayments;
}
var maxMortgageTotal = maxLoanPrincipal + downPayment;
// Display results
maxMortgageAmountElement.textContent = "$" + maxLoanPrincipal.toFixed(2);
notesElement.textContent = "This estimate is based on your desired monthly payment for Principal & Interest only, the given interest rate, and loan term. It does NOT include property taxes, homeowner's insurance, or HOA fees, which will increase your total monthly housing cost.";
notesElement.style.color = "#6c757d"; // Reset color to default
}