Understanding how much mortgage you can afford is a crucial step in the home-buying process. This calculator helps you estimate your maximum affordable mortgage based on your income, debts, and estimated interest rates. Remember, this is an estimate, and your actual borrowing power will be determined by lenders after a full credit assessment.
How Mortgage Affordability is Calculated
Lenders typically use a debt-to-income (DTI) ratio to assess your ability to repay a mortgage. There are generally two DTI ratios they consider:
Front-end ratio (Housing Ratio): This measures the percentage of your gross monthly income that would go towards your mortgage payment (principal, interest, property taxes, homeowners insurance, and potentially HOA dues). Lenders often prefer this to be no more than 28%.
Back-end ratio (Total DTI): This measures the percentage of your gross monthly income that would go towards all your monthly debt obligations, including your potential mortgage payment. Lenders often prefer this to be no more than 36% to 43%, depending on the loan type and your creditworthiness.
Our calculator uses a simplified approach. It estimates the maximum monthly payment you can afford by considering your gross monthly income and existing debts, aiming to keep your total DTI within a common guideline (e.g., 36%). It then calculates the maximum loan amount you could borrow for that monthly payment based on the provided interest rate and loan term. Your down payment is then added to this loan amount to estimate your maximum affordable home price.
Key Factors:
Gross Monthly Income: The total income you earn before taxes and deductions.
Current Monthly Debts: Includes minimum payments on credit cards, car loans, student loans, personal loans, and any other recurring debt.
Down Payment: The upfront cash you pay towards the home purchase. A larger down payment reduces the loan amount needed.
Interest Rate: The annual interest rate on the mortgage. Higher rates mean higher monthly payments for the same loan amount.
Loan Term: The number of years you have to repay the loan. Shorter terms have higher monthly payments but less total interest paid.
Important Note: This calculator provides an estimate. Actual mortgage affordability depends on lender policies, your credit score, loan type, property taxes, homeowners insurance, and other factors. It's always best to speak with a mortgage professional for a personalized assessment.
function calculateMortgageAffordability() {
var grossMonthlyIncome = parseFloat(document.getElementById("grossMonthlyIncome").value);
var currentMonthlyDebts = parseFloat(document.getElementById("currentMonthlyDebts").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var resultDiv = document.getElementById("result");
// Clear previous results and errors
resultDiv.innerHTML = "";
// Input validation
if (isNaN(grossMonthlyIncome) || grossMonthlyIncome < 0 ||
isNaN(currentMonthlyDebts) || currentMonthlyDebts < 0 ||
isNaN(downPayment) || downPayment < 0 ||
isNaN(interestRate) || interestRate < 0 ||
isNaN(loanTermYears) || loanTermYears <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Lender typically allows for a total DTI of around 36% (this can vary)
// Let's use 36% as a common guideline for maximum total debt payments
var maxTotalDebtPaymentPercentage = 0.36;
var maxTotalDebtPayment = grossMonthlyIncome * maxTotalDebtPaymentPercentage;
// Maximum allowable monthly mortgage payment is the max total debt minus current debts
var maxMonthlyMortgagePayment = maxTotalDebtPayment – currentMonthlyDebts;
// Ensure maxMonthlyMortgagePayment is not negative
if (maxMonthlyMortgagePayment 0) {
// Formula for present value of an annuity (loan amount)
// PV = PMT * [1 – (1 + r)^-n] / r
maxLoanAmount = maxMonthlyMortgagePayment * (1 – Math.pow(1 + monthlyInterestRate, -numberOfPayments)) / monthlyInterestRate;
} else if (maxMonthlyMortgagePayment > 0) {
// If interest rate is 0, loan amount is simply payment times number of periods
maxLoanAmount = maxMonthlyMortgagePayment * numberOfPayments;
}
// Maximum affordable home price is the max loan amount plus the down payment
var maxAffordableHomePrice = maxLoanAmount + downPayment;
// Format the results
var formattedMaxMonthlyMortgagePayment = maxMonthlyMortgagePayment.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxLoanAmount = maxLoanAmount.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxAffordableHomePrice = maxAffordableHomePrice.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
// Display the results
resultDiv.innerHTML =
"