Determining how much house you can afford is a crucial step in the home-buying process.
This calculator helps estimate your potential mortgage affordability by considering several key financial factors.
It's important to remember that this is an estimate, and your actual borrowing capacity may vary based on lender
specifics, credit score, debt-to-income ratios, and market conditions.
Key Factors Explained:
Annual Household Income: This is your total gross income from all sources before taxes. Lenders often look at this to gauge your ability to repay the loan.
Total Monthly Debt Payments: This includes minimum payments on credit cards, auto loans, student loans, personal loans, and any other recurring debt obligations. Lenders use this to calculate your Debt-to-Income (DTI) ratio.
Down Payment: The upfront cash you pay towards the home purchase. A larger down payment reduces the loan amount needed and can lead to better interest rates and lower monthly payments.
Estimated Mortgage Interest Rate: The annual interest rate you expect to pay on your mortgage. This significantly impacts your monthly payment and the total interest paid over the life of the loan.
Mortgage Loan Term: The number of years you have to repay the mortgage loan. Common terms are 15 and 30 years. Shorter terms mean higher monthly payments but less total interest paid.
Estimated Annual Property Taxes: Taxes levied by local governments on your property. These are typically paid monthly as part of your mortgage payment (escrow).
Estimated Annual Homeowners Insurance: Insurance that protects your home against damage or loss. This is also usually paid monthly via escrow.
How the Calculation Works (Simplified):
This calculator uses common lending guidelines, primarily focusing on the 28/36 rule (though actual lender ratios can vary).
The 28% rule suggests that your total housing costs (principal, interest, taxes, insurance – PITI) should not exceed 28% of your gross monthly income.
The 36% rule suggests that all your monthly debt obligations, including your potential mortgage payment, should not exceed 36% of your gross monthly income.
Our calculator estimates the maximum loan amount you could qualify for based on these principles, considering your down payment, interest rate, loan term, and other housing costs.
Disclaimer: This calculator is for informational purposes only and does not constitute financial advice. Consult with a mortgage professional for personalized guidance.
function calculateMortgageAffordability() {
var annualIncome = parseFloat(document.getElementById("annualIncome").value);
var existingDebt = parseFloat(document.getElementById("existingDebt").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseInt(document.getElementById("loanTerm").value);
var propertyTaxes = parseFloat(document.getElementById("propertyTaxes").value);
var homeInsurance = parseFloat(document.getElementById("homeInsurance").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(annualIncome) || annualIncome <= 0 ||
isNaN(existingDebt) || existingDebt < 0 ||
isNaN(downPayment) || downPayment < 0 ||
isNaN(interestRate) || interestRate <= 0 ||
isNaN(loanTerm) || loanTerm <= 0 ||
isNaN(propertyTaxes) || propertyTaxes < 0 ||
isNaN(homeInsurance) || homeInsurance < 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
var monthlyIncome = annualIncome / 12;
// Calculate maximum PITI (Principal, Interest, Taxes, Insurance) based on 28% rule
var maxPITI = monthlyIncome * 0.28;
// Calculate maximum total debt based on 36% rule
var maxTotalDebt = monthlyIncome * 0.36;
// Maximum allowable monthly mortgage payment (P&I) based on 36% rule, after subtracting existing debt and estimated taxes/insurance
var maxMortgagePayment = maxTotalDebt – existingDebt;
var monthlyPropertyTaxes = propertyTaxes / 12;
var monthlyHomeInsurance = homeInsurance / 12;
maxMortgagePayment = maxMortgagePayment – monthlyPropertyTaxes – monthlyHomeInsurance;
// Ensure maxMortgagePayment isn't negative
if (maxMortgagePayment < 0) {
maxMortgagePayment = 0;
}
// The actual maximum mortgage payment is the lower of the two limits derived from the 28% and 36% rules.
// However, the 36% rule already incorporates existing debt, taxes, and insurance, making it the more restrictive for loan amount calculation when PITI is involved.
// We'll use the maxMortgagePayment derived from the 36% rule as it's more comprehensive after accounting for non-P&I costs.
var affordableMonthlyPayment = maxMortgagePayment; // Use the more restrictive value after accounting for all other debts and costs
// If the 28% rule results in a lower PITI, we should also cap the affordable payment.
// However, since maxMortgagePayment already subtracts taxes and insurance, we compare the resulting P&I to the 28% derived PITI.
var pniAllowedBy28Rule = maxPITI – monthlyPropertyTaxes – monthlyHomeInsurance;
if (pniAllowedBy28Rule 0 && affordableMonthlyPayment > 0) {
var numerator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
if (denominator > 0) {
maxLoanAmount = affordableMonthlyPayment * (numerator / denominator);
}
} else if (affordableMonthlyPayment === 0) {
maxLoanAmount = 0;
} else if (monthlyInterestRate === 0) { // Handle zero interest rate case (rare, but for completeness)
maxLoanAmount = affordableMonthlyPayment * numberOfPayments;
}
var estimatedMaxHomePrice = maxLoanAmount + downPayment;
// Format results for display
var formattedMaxLoanAmount = maxLoanAmount.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedEstimatedMaxHomePrice = estimatedMaxHomePrice.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMonthlyPITI = (affordableMonthlyPayment + monthlyPropertyTaxes + monthlyHomeInsurance).toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxMortgagePayment = affordableMonthlyPayment.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
resultDiv.innerHTML = `
Estimated Maximum Loan Amount: ${formattedMaxLoanAmount}
Estimated Maximum Home Price (incl. Down Payment): ${formattedEstimatedMaxHomePrice}
Estimated Maximum Monthly PITI Payment: ${formattedMonthlyPITI}
Estimated Maximum Monthly Principal & Interest Payment: ${formattedMaxMortgagePayment}
`;
}