Please enter valid numerical values for income and down payment.
Maximum Home Price You Can Afford
$0
$0Max Monthly Payment
$0Loan Amount
0%Limiting DTI Ratio
How Much House Can I Really Afford?
Before you start attending open houses or scrolling through listings, it is critical to understand your financial limits. This Mortgage Affordability Calculator uses the industry-standard 28/36 Rule to determine a realistic home buying budget based on your income, existing debts, and down payment savings.
Understanding the 28/36 Rule
Lenders use Debt-to-Income (DTI) ratios to decide how much money they are willing to lend you. This calculator evaluates affordability based on two key thresholds:
The Front-End Ratio (28%): Housing costs (mortgage principal, interest, taxes, and insurance) should not exceed 28% of your gross monthly income.
The Back-End Ratio (36%): Your total monthly debt payments (housing costs + car loans, student loans, credit cards) should not exceed 36% of your gross monthly income.
The calculator determines your maximum monthly payment based on the lower (more conservative) of these two limits to ensure you don't become "house poor."
Key Factors Affecting Your Purchasing Power
Several variables impact the final price of the home you can afford:
Interest Rates: A higher interest rate increases your monthly payment, significantly reducing the loan amount you qualify for. Even a 1% difference can change your buying power by tens of thousands of dollars.
Down Payment: A larger down payment reduces the loan principal and eliminates the need for Private Mortgage Insurance (PMI) if you put down 20% or more. This allows more of your monthly budget to go toward the home price rather than fees.
Monthly Debts: High monthly obligations (like a large car payment) eat into your Back-End ratio. Paying off a credit card or a small loan before applying for a mortgage can often boost your affordability significantly.
What is Included in the Estimated Payment?
This calculator estimates your PITI: Principal, Interest, Taxes, and Insurance. It assumes a standard estimate for property taxes and homeowner's insurance based on the home's value. Keep in mind that if you purchase a property in an area with high HOA fees, your purchasing power will decrease further.
function calculateAffordability() {
// 1. Get Input Values
var annualIncome = parseFloat(document.getElementById('mac_annual_income').value);
var monthlyDebt = parseFloat(document.getElementById('mac_monthly_debt').value) || 0;
var downPayment = parseFloat(document.getElementById('mac_down_payment').value) || 0;
var interestRate = parseFloat(document.getElementById('mac_interest_rate').value);
var years = parseInt(document.getElementById('mac_loan_term').value);
var taxInsRate = parseFloat(document.getElementById('mac_tax_insurance').value) || 1.5;
// 2. Validation
var errorMsg = document.getElementById('mac_error_msg');
if (isNaN(annualIncome) || annualIncome <= 0 || isNaN(interestRate) || isNaN(years)) {
errorMsg.style.display = 'block';
document.getElementById('mac_results_area').style.display = 'none';
return;
}
errorMsg.style.display = 'none';
// 3. Logic: Determine Max Allowable Monthly Payment
var grossMonthlyIncome = annualIncome / 12;
// Front-End Ratio Limit (28% of income for housing)
var limitFront = grossMonthlyIncome * 0.28;
// Back-End Ratio Limit (36% of income for housing + debts)
var limitBack = (grossMonthlyIncome * 0.36) – monthlyDebt;
// The maximum payment is the lesser of the two
var maxMonthlyPayment = Math.min(limitFront, limitBack);
var limitingRatio = (limitFront < limitBack) ? "28% (Front-End)" : "36% (Back-End)";
if (maxMonthlyPayment <= 0) {
document.getElementById('mac_home_price').innerHTML = "$0";
document.getElementById('mac_monthly_payment').innerHTML = "$0";
document.getElementById('mac_loan_amount').innerHTML = "$0";
document.getElementById('mac_dti_used').innerHTML = "N/A";
document.getElementById('mac_results_area').style.display = 'block';
return;
}
// 4. Reverse Calculate Home Price
// Formula: Price = (MaxPayment + DownPayment * K) / (K + MonthlyTaxInsRate)
// Where K is the mortgage constant (factor)
var r = interestRate / 100 / 12; // Monthly interest rate
var n = years * 12; // Total number of payments
// Mortgage Constant (K) calculation
var K = 0;
if (r === 0) {
K = 1 / n;
} else {
K = (r * Math.pow(1 + r, n)) / (Math.pow(1 + r, n) – 1);
}
var monthlyTaxInsFactor = (taxInsRate / 100) / 12;
// Algebraic solution derived from:
// MaxPayment = (Price – DownPayment) * K + (Price * monthlyTaxInsFactor)
var maxHomePrice = (maxMonthlyPayment + (downPayment * K)) / (K + monthlyTaxInsFactor);
// Edge case: If down payment is greater than home price logic (cash buy scenario not fully handled by mortgage calc usually, but mathematically:)
if (maxHomePrice < downPayment) {
maxHomePrice = downPayment; // You can afford at least what you have in cash
}
var maxLoanAmount = maxHomePrice – downPayment;
if (maxLoanAmount < 0) maxLoanAmount = 0;
// 5. Output Formatting
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
maximumFractionDigits: 0
});
document.getElementById('mac_home_price').innerHTML = formatter.format(maxHomePrice);
document.getElementById('mac_monthly_payment').innerHTML = formatter.format(maxMonthlyPayment);
document.getElementById('mac_loan_amount').innerHTML = formatter.format(maxLoanAmount);
document.getElementById('mac_dti_used').innerHTML = limitingRatio;
document.getElementById('mac_results_area').style.display = 'block';
}