Please enter valid positive numbers for Income, Interest Rate, and Down Payment.
Maximum Home Price:$0
Loan Amount:$0
Est. Monthly Payment (PITI):$0
Principal & Interest:$0
Taxes, Insurance & HOA:$0
*Based on standard 28% front-end and 36% back-end DTI ratios.
function calculateAffordability() {
// 1. Get Inputs
var annualIncome = parseFloat(document.getElementById('annualIncome').value);
var monthlyDebts = parseFloat(document.getElementById('monthlyDebts').value) || 0;
var downPayment = parseFloat(document.getElementById('downPayment').value) || 0;
var interestRate = parseFloat(document.getElementById('interestRate').value);
var loanTermYears = parseInt(document.getElementById('loanTerm').value);
var propertyTaxRate = parseFloat(document.getElementById('propertyTax').value) || 1.2;
var insuranceRate = parseFloat(document.getElementById('insuranceRate').value) || 0.5;
var hoaFees = parseFloat(document.getElementById('hoaFees').value) || 0;
// 2. Validation
var errorDiv = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('results');
if (isNaN(annualIncome) || annualIncome <= 0 || isNaN(interestRate) || interestRate <= 0) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
// 3. Calculation Logic
// Convert rates to decimals
var monthlyIncome = annualIncome / 12;
var r = (interestRate / 100) / 12; // Monthly interest rate
var n = loanTermYears * 12; // Total months
// Tax and Insurance Monthly Rates (as decimal of home price)
var taxRateMonthly = (propertyTaxRate / 100) / 12;
var insuranceRateMonthly = (insuranceRate / 100) / 12;
// Calculate Allowable Monthly Payment based on DTI Rules
// Rule 1: Front-end ratio (Housing costs <= 28% of gross income)
var maxHousingFront = monthlyIncome * 0.28;
// Rule 2: Back-end ratio (Total debts <= 36% of gross income)
var maxTotalBack = monthlyIncome * 0.36;
var maxHousingBack = maxTotalBack – monthlyDebts;
// Take the lower of the two limits
var maxAllowablePayment = Math.min(maxHousingFront, maxHousingBack);
// If debts are too high, affordability might be 0
if (maxAllowablePayment <= hoaFees) {
document.getElementById('resHomePrice').innerText = "$0";
document.getElementById('resLoanAmount').innerText = "$0";
document.getElementById('resMonthlyPayment').innerText = "$0";
document.getElementById('resPI').innerText = "$0";
document.getElementById('resTaxesIns').innerText = "Debts too high";
resultsDiv.style.display = 'block';
return;
}
// Subtract HOA from allowable payment to find amount available for PITI + Tax + Ins
var availableForMortgageAndEscrow = maxAllowablePayment – hoaFees;
// Mortgage Factor formula: (r(1+r)^n) / ((1+r)^n – 1)
var mortgageFactor = (r * Math.pow(1 + r, n)) / (Math.pow(1 + r, n) – 1);
// Solve for Home Price (H)
// Equation: Available = (Loan * Factor) + (H * TaxRate) + (H * InsRate)
// Since Loan = H – DownPayment
// Available = ((H – DownPayment) * Factor) + (H * (TaxRate + InsRate))
// Available = (H * Factor) – (DownPayment * Factor) + (H * CombinedRate)
// Available + (DownPayment * Factor) = H * (Factor + CombinedRate)
// H = (Available + (DownPayment * Factor)) / (Factor + TaxRate + InsRate)
var combinedEscrowRate = taxRateMonthly + insuranceRateMonthly;
var maxHomePrice = (availableForMortgageAndEscrow + (downPayment * mortgageFactor)) / (mortgageFactor + combinedEscrowRate);
// Edge case: If calculation results in negative or invalid number
if (maxHomePrice < 0) maxHomePrice = 0;
var loanAmount = Math.max(0, maxHomePrice – downPayment);
var principalInterest = loanAmount * mortgageFactor;
var taxesInsurance = (maxHomePrice * combinedEscrowRate) + hoaFees;
var totalMonthly = principalInterest + taxesInsurance;
// 4. Update UI
// Helper function for currency formatting
var fmt = new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD', maximumFractionDigits: 0 });
document.getElementById('resHomePrice').innerText = fmt.format(maxHomePrice);
document.getElementById('resLoanAmount').innerText = fmt.format(loanAmount);
document.getElementById('resMonthlyPayment').innerText = fmt.format(totalMonthly);
document.getElementById('resPI').innerText = fmt.format(principalInterest);
document.getElementById('resTaxesIns').innerText = fmt.format(taxesInsurance);
resultsDiv.style.display = 'block';
}
Understanding Your Mortgage Affordability
Purchasing a home is likely the largest financial commitment you will make in your lifetime. Before browsing listings or attending open houses, it is crucial to determine exactly how much house you can afford. This Mortgage Affordability Calculator uses standard lender formulas to give you a realistic estimate of your purchasing power based on your income, debts, and current interest rates.
The 28/36 Rule Explained
Lenders typically use two specific Debt-to-Income (DTI) ratios to determine if you qualify for a loan. These are often referred to as the "28/36 Rule":
Front-End Ratio (28%): This rule states that your monthly housing costs—including principal, interest, property taxes, and insurance (PITI)—should not exceed 28% of your gross monthly income.
Back-End Ratio (36%): This rule looks at your total debt load. Your housing costs plus all other monthly debts (student loans, credit cards, car payments, alimony) should not exceed 36% of your gross monthly income.
Our calculator checks both of these ratios and uses the lower number to determine your maximum safe budget. While some loan programs (like FHA or VA loans) may allow higher ratios, sticking to the 28/36 rule is generally considered a safe financial strategy.
Key Factors That Impact Affordability
Several variables influence how much money a bank will lend you:
Income: Higher gross annual income directly increases your borrowing capacity.
Monthly Debts: High monthly obligations (like an expensive car payment) significantly reduce your buying power because they eat into the 36% back-end ratio.
Down Payment: A larger down payment reduces the loan amount required, which lowers your monthly payments. It also provides instant equity in the home.
Interest Rates: Even a small increase in interest rates can drastically reduce your maximum home price, as more of your monthly payment goes toward interest rather than principal.
Property Taxes & HOA: Don't forget these "hidden" costs. High property taxes or Homeowner Association (HOA) fees reduce the amount of mortgage you can carry.
How to Improve Your Home Buying Power
If the results from the calculator are lower than you hoped, consider these strategies to increase your affordability:
Pay Down Debt: Reducing monthly recurring debts is the fastest way to improve your DTI ratio.
Save for a Larger Down Payment: This reduces the amount you need to borrow and may eliminate the need for Private Mortgage Insurance (PMI).
Improve Your Credit Score: A better credit score often qualifies you for lower interest rates, which lowers your monthly payment and boosts your purchasing power.
Use this tool as a starting point for your home buying journey. Once you have an estimate, consult with a mortgage professional to get pre-approved for a loan.