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 maximum loan amount based on your income, debts, and down payment. By inputting these details, you can gain a clearer picture of your budget and what you can realistically borrow from a lender.
How Mortgage Affordability Works
Lenders assess your ability to repay a mortgage by looking at several key factors. The most common method is the debt-to-income ratio (DTI). This ratio compares your total monthly debt payments (including the estimated mortgage payment) to your gross monthly income.
Front-end DTI (Housing Ratio): This typically looks at your potential housing costs (principal, interest, taxes, and insurance – PITI) and compares it to your gross monthly income. Many lenders prefer this to be no more than 28%.
Back-end DTI (Total Debt Ratio): This considers all your monthly debt obligations, including credit cards, student loans, car payments, and your potential PITI, and compares it to your gross monthly income. Lenders often prefer this ratio to be no more than 36%, though some may go higher.
This calculator focuses on estimating your maximum loan amount by considering your income, existing debts, and the down payment you plan to make, while aiming for a common DTI threshold.
Using the Calculator
Simply fill in the fields below with your financial information. The calculator will then provide an estimated maximum loan amount. Remember, this is an estimate, and your actual borrowing power may vary based on lender policies, credit score, interest rates, and other factors.
function calculateAffordability() {
var grossMonthlyIncome = parseFloat(document.getElementById("grossMonthlyIncome").value);
var existingMonthlyDebt = parseFloat(document.getElementById("existingMonthlyDebt").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var estimatedInterestRate = parseFloat(document.getElementById("estimatedInterestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var estimatedTaxesInsurance = parseFloat(document.getElementById("estimatedTaxesInsurance").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(grossMonthlyIncome) || grossMonthlyIncome <= 0 ||
isNaN(existingMonthlyDebt) || existingMonthlyDebt < 0 ||
isNaN(downPayment) || downPayment < 0 ||
isNaN(estimatedInterestRate) || estimatedInterestRate <= 0 ||
isNaN(loanTermYears) || loanTermYears <= 0 ||
isNaN(estimatedTaxesInsurance) || estimatedTaxesInsurance < 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Common DTI target (e.g., 36% total DTI)
var maxTotalDebtPayment = grossMonthlyIncome * 0.36;
var maxMortgagePaymentAllowed = maxTotalDebtPayment – existingMonthlyDebt;
if (maxMortgagePaymentAllowed <= 0) {
resultDiv.innerHTML = "Based on your income and existing debts, your capacity for a mortgage payment may be limited. Consider increasing income or reducing debt.";
return;
}
// Annual taxes and insurance divided by 12 for monthly cost
var monthlyTaxesInsurance = estimatedTaxesInsurance / 12;
// Subtract monthly taxes and insurance from the maximum mortgage payment allowed
var maxPrincipalInterestPayment = maxMortgagePaymentAllowed – monthlyTaxesInsurance;
if (maxPrincipalInterestPayment 0) {
maxLoanAmount = maxPrincipalInterestPayment * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
} else { // Handle case of 0% interest rate, though highly unlikely for a mortgage
maxLoanAmount = maxPrincipalInterestPayment * numberOfPayments;
}
var estimatedMaxLoan = maxLoanAmount;
var estimatedAffordableHomePrice = estimatedMaxLoan + downPayment;
resultDiv.innerHTML =
"
Estimated Affordability
" +
"Estimated Maximum Loan Amount: $" + estimatedMaxLoan.toFixed(2) + "" +
"Estimated Maximum Affordable Home Price: $" + estimatedAffordableHomePrice.toFixed(2) + "" +
"This calculation is based on a 36% total debt-to-income ratio and the figures provided. Actual loan approval and amounts may vary.";
}