Determining how much house you can afford is a crucial step in the home-buying process. This calculator helps you estimate your potential borrowing power by considering your income, existing debts, down payment, and the terms of the mortgage itself. Lenders typically use debt-to-income ratios (DTI) to assess your ability to manage monthly payments. A common guideline is that your total housing expenses (principal, interest, taxes, insurance – PITI) should not exceed 28% of your gross monthly income, and your total debt obligations (including PITI) should not exceed 36% of your gross monthly income. This calculator uses these principles, along with your provided information, to give you an estimated maximum loan amount you might qualify for, and consequently, an approximate maximum home price.
Annual Household Income: This is your total gross income before taxes. Lenders will look at this to determine your capacity to repay a loan.
Monthly Debt Payments: This includes all your existing monthly financial obligations such as car payments, student loan payments, minimum credit card payments, and any other recurring loan payments. These are subtracted from your income to determine how much is available for a mortgage.
Down Payment: The amount of money you pay upfront towards the purchase price of the home. A larger down payment reduces the loan amount needed and can improve your loan terms.
Estimated Mortgage Interest Rate: This is the annual interest rate you expect to pay on your mortgage. Even small differences in interest rates can significantly impact your monthly payments and the total cost of the loan over time.
Mortgage Loan Term: This is the number of years you have to repay the mortgage. Common terms are 15 or 30 years. A shorter term means higher monthly payments but less interest paid overall.
Note: This calculator provides an *estimate* only. Actual loan approval and amounts will depend on a lender's specific underwriting criteria, your credit score, property appraisal, and other factors. It's always recommended to speak with a mortgage professional for personalized advice.
function calculateMortgageAffordability() {
var annualIncome = parseFloat(document.getElementById("annualIncome").value);
var currentDebts = parseFloat(document.getElementById("currentDebts").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value) / 100; // Convert percentage to decimal
var loanTerm = parseInt(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(annualIncome) || isNaN(currentDebts) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
annualIncome < 0 || currentDebts < 0 || downPayment < 0 || interestRate < 0 || loanTerm <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Calculate gross monthly income
var grossMonthlyIncome = annualIncome / 12;
// — Lender Guidelines (Commonly used DTI ratios) —
// 28% rule for housing (PITI)
var maxHousingPayment = grossMonthlyIncome * 0.28;
// 36% rule for total debt (including PITI)
var maxTotalDebtPayment = grossMonthlyIncome * 0.36;
// Calculate the maximum allowable monthly debt payment from PITI
var maxMortgagePayment = maxTotalDebtPayment – currentDebts;
// Ensure maxMortgagePayment is not negative
if (maxMortgagePayment 0 && numberOfPayments > 0) {
var factor = Math.pow(1 + monthlyInterestRate, numberOfPayments);
maxLoanAmount = affordableMonthlyPITI * (factor – 1) / (monthlyInterestRate * factor);
} else if (monthlyInterestRate === 0) { // Handle 0% interest rate scenario
maxLoanAmount = affordableMonthlyPITI * numberOfPayments;
}
// Since PITI includes Principal, Interest, Taxes, and Insurance, and we've only calculated P&I,
// we need to estimate Taxes and Insurance to get a more accurate house price.
// Let's assume taxes and insurance are roughly 1.2% of the home value annually (this is a simplification).
// So, monthly taxes and insurance would be (Home Price * 0.012) / 12 = Home Price * 0.0001
// var Home Price = HP.
// Then, P&I = affordableMonthlyPITI – (HP * 0.0001)
// We know the max loan amount is based on P&I. So, maxLoanAmount = P&I.
// maxLoanAmount = affordableMonthlyPITI – (HP * 0.0001)
// HP * 0.0001 = affordableMonthlyPITI – maxLoanAmount
// HP = (affordableMonthlyPITI – maxLoanAmount) / 0.0001
// This formula only makes sense if affordableMonthlyPITI is GREATER than maxLoanAmount (which it should be if we're accounting for taxes/insurance).
var estimatedMonthlyTaxesAndInsurance = 0;
var estimatedMaxHomePrice = 0;
// A more direct approach is to assume taxes/insurance as a % of the loan amount or a fixed value for estimation.
// For simplicity in this calculator, we'll focus on the loan amount the P&I portion can support,
// and then add a typical estimate for taxes and insurance to get a rough home price.
// A common estimate for PITI is around 1% of the home value per month (split between taxes, insurance, possibly HOA).
// If PITI is ~1% of HP, then P&I is roughly 0.75% of HP (assuming 0.25% for T&I).
// So, maxLoanAmount = HP * 0.0075 (very rough)
// HP = maxLoanAmount / 0.0075
// Or, let's use a simpler estimate: If affordableMonthlyPITI is the target, and we assume T&I are, say, $300/month.
// Then P&I = affordableMonthlyPITI – 300. Then calculate loan amount.
// OR, we can estimate taxes and insurance as a percentage of the *loan amount* for simplicity in this calculator's output.
// Let's assume taxes and insurance add about 0.1% of the loan amount per month to the payment.
// So, affordableMonthlyPITI = (Principal + Interest) + (Taxes + Insurance)
// Let's estimate P&I = affordableMonthlyPITI * 0.8 (assuming 20% for taxes/insurance, which is very rough)
// Then, we calculate the loan amount for this estimated P&I.
var estimatedMonthlyPI = affordableMonthlyPITI * 0.8; // Rough split: 80% P&I, 20% T&I
if (monthlyInterestRate > 0 && numberOfPayments > 0) {
var factor = Math.pow(1 + monthlyInterestRate, numberOfPayments);
maxLoanAmount = estimatedMonthlyPI * (factor – 1) / (monthlyInterestRate * factor);
} else if (monthlyInterestRate === 0) {
maxLoanAmount = estimatedMonthlyPI * numberOfPayments;
}
// Now, estimate the maximum home price by adding back the estimated monthly T&I to the P&I payment,
// and then accounting for the down payment.
// Estimated monthly T&I could be a fixed amount or a percentage of the home value.
// For a simple estimate, let's assume T&I add roughly $300/month per $100k of loan value.
// Or, let's use a fixed estimate per month for T&I, e.g., $300.
var estimatedMonthlyTaxesAndInsuranceFixed = 300; // This is a very rough estimate.
var actualMonthlyPITI_Estimate = estimatedMonthlyPI + estimatedMonthlyTaxesAndInsuranceFixed;
// Re-calculate max loan amount based on the more accurate PITI target and the assumption of fixed T&I.
// If affordableMonthlyPITI is our target, and we reserve $300 for T&I, then P&I = affordableMonthlyPITI – 300.
var revisedMonthlyPI = affordableMonthlyPITI – estimatedMonthlyTaxesAndInsuranceFixed;
if (revisedMonthlyPI 0 && numberOfPayments > 0) {
var factor = Math.pow(1 + monthlyInterestRate, numberOfPayments);
revisedMaxLoanAmount = revisedMonthlyPI * (factor – 1) / (monthlyInterestRate * factor);
} else if (monthlyInterestRate === 0) {
revisedMaxLoanAmount = revisedMonthlyPI * numberOfPayments;
}
estimatedMaxHomePrice = revisedMaxLoanAmount + downPayment;
// Display Results
resultDiv.innerHTML =
"Estimated Maximum Monthly P&I Payment: $" + estimatedMonthlyPI.toFixed(2) + "" +
"Estimated Monthly Taxes & Insurance: $" + estimatedMonthlyTaxesAndInsuranceFixed.toFixed(2) + " (Estimate)" +
"Estimated Maximum Affordable Monthly PITI: $" + affordableMonthlyPITI.toFixed(2) + "" +
"Estimated Maximum Loan Amount: $" + revisedMaxLoanAmount.toFixed(2) + "" +
"Estimated Maximum Home Price: $" + estimatedMaxHomePrice.toFixed(2) + "";
}
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font-family: sans-serif;
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max-width: 600px;
margin: 20px auto;
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cursor: pointer;
transition: background-color 0.3s ease;
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.calculator-container button:hover {
background-color: #0056b3;
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.calculator-result {
margin-top: 25px;
padding: 15px;
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border: 1px solid #ced4da;
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/* Responsive adjustments */
@media (max-width: 480px) {
.calculator-inputs {
grid-template-columns: 1fr;
}
.calculator-container {
padding: 15px;
}
.calculator-container h2 {
font-size: 1.5rem;
}
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font-size: 1rem;
padding: 10px 15px;
}
}