Mortgage Affordability Calculator
Understanding how much house you can afford is a crucial first step in the home-buying process. Our Mortgage Affordability Calculator helps you estimate your potential borrowing power based on your income, debts, and down payment. This tool takes into account your gross monthly income, existing monthly debt payments, and the size of your down payment to provide a realistic estimate of the mortgage amount you might qualify for.
Key Factors:
- Gross Monthly Income: This is your income before taxes and other deductions. Lenders typically want to see that your housing costs (including mortgage, property taxes, and insurance) don't exceed a certain percentage of this income (often around 28%-36%).
- Existing Monthly Debt Payments: This includes all your recurring monthly debt obligations, such as car loans, student loans, credit card minimum payments, and any other loans. Lenders use this to calculate your debt-to-income ratio (DTI), which is usually capped at 36%-43%.
- Down Payment: The upfront cash you pay towards the purchase price of the home. A larger down payment reduces the loan amount needed and can improve your chances of approval and potentially secure a better interest rate.
- Estimated Interest Rate: This is the annual interest rate you expect on your mortgage. Rates fluctuate based on market conditions and your creditworthiness.
- Loan Term (Years): The duration of your mortgage, typically 15 or 30 years. A shorter term means higher monthly payments but less interest paid overall.
By inputting these details, you'll get an estimated maximum mortgage amount. Remember, this is an estimate, and your actual borrowing capacity will be determined by a mortgage lender after a full review of your financial situation.
15 Years
30 Years
function calculateMortgageAffordability() {
var grossMonthlyIncome = parseFloat(document.getElementById("grossMonthlyIncome").value);
var monthlyDebtPayments = parseFloat(document.getElementById("monthlyDebtPayments").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRatePercent = parseFloat(document.getElementById("estimatedInterestRate").value);
var loanTermYears = parseInt(document.getElementById("loanTermYears").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "; // Clear previous results
if (isNaN(grossMonthlyIncome) || isNaN(monthlyDebtPayments) || isNaN(downPayment) || isNaN(interestRatePercent) || isNaN(loanTermYears)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
// Assume a maximum total housing expense ratio (PITI – Principal, Interest, Taxes, Insurance) of 36%
// Assume property taxes and insurance are roughly 1.2% of the home price annually, or 0.1% monthly.
// This is a simplification, actual PITI varies greatly by location.
var maxHousingPaymentRatio = 0.36;
var estimatedPitiRatioPerMonth = 0.001; // 0.1% for taxes and insurance monthly
// Calculate maximum affordable monthly payment for PITI
var maxTotalMonthlyPayment = (grossMonthlyIncome * maxHousingPaymentRatio);
// Subtract existing debt payments
var maxPrincipalInterestPayment = maxTotalMonthlyPayment – monthlyDebtPayments;
if (maxPrincipalInterestPayment 0 && numberOfPayments > 0) {
var numerator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
if (denominator > 0) {
maxLoanAmount = maxPrincipalInterestPayment * numerator / denominator;
}
} else if (monthlyInterestRate === 0 && numberOfPayments > 0) { // Handle 0% interest rate
maxLoanAmount = maxPrincipalInterestPayment * numberOfPayments;
}
// Now, consider the portion of the maxPrincipalInterestPayment that goes to taxes and insurance.
// var P be the loan amount, T be taxes/insurance per month.
// maxPrincipalInterestPayment = maxLoanAmount + T
// We need to find P such that P + T = maxPrincipalInterestPayment.
// If we assume taxes/insurance is a fixed percentage of the *loan amount*, it becomes iterative.
// A simpler approach: assume the maximum P&I payment is a *part* of the total max housing payment,
// and the rest is for taxes and insurance.
// Let's adjust the calculation to directly estimate the maximum home price.
// var P be the loan amount, and H be the total home price. H = P + DownPayment
// Monthly PITI = (P * i) / (1 – (1 + i)^-n) + (H * estimatedPitiRatioPerMonth)
// This max PITI should be <= maxTotalMonthlyPayment
// (P * i) / (1 – (1 + i)^-n) + ((P + DownPayment) * estimatedPitiRatioPerMonth) <= maxTotalMonthlyPayment
// This is hard to solve directly for P. Let's use an iterative approach or a simpler approximation.
// Approximation: Assume taxes and insurance are a fixed amount per month derived from income.
// Let's stick to estimating the *loan amount* first, and then we can infer the maximum *home price*.
// The maxLoanAmount calculated above is the maximum *principal and interest* you can afford.
// If we assume a certain percentage of the *total housing payment* goes to P&I, we can work backwards.
// Let's say P&I is 85% of the total housing payment, and 15% is for taxes/insurance.
// maxPrincipalInterestPayment = maxTotalMonthlyPayment * 0.85
// Then calculate maxLoanAmount from this adjusted P&I payment.
// Let's use a more common approach: Maximum Debt-to-Income Ratio (DTI).
// Max total monthly debt (including PITI) is typically 36%-43% of gross monthly income.
// Let's use 43% as a higher end for DTI.
var maxDtiRatio = 0.43;
var maxTotalObligations = grossMonthlyIncome * maxDtiRatio;
var maxPrincipalInterestAndTaxesInsurance = maxTotalObligations – monthlyDebtPayments;
if (maxPrincipalInterestAndTaxesInsurance 0 && numberOfPayments > 0) {
monthlyRateFactor = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments) / (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1);
} else if (monthlyInterestRate === 0 && numberOfPayments > 0) {
monthlyRateFactor = 1; // Simplified for 0% interest
}
var affordableLoanAmount = 0;
var denominatorForLoanAmount = monthlyRateFactor + estimatedPitiRatioPerMonth;
if (denominatorForLoanAmount > 0) {
var numeratorForLoanAmount = maxPrincipalInterestAndTaxesInsurance – (downPayment * estimatedPitiRatioPerMonth);
if (numeratorForLoanAmount > 0) {
affordableLoanAmount = numeratorForLoanAmount / denominatorForLoanAmount;
} else {
// This happens if the down payment + estimated taxes/insurance already exceeds the max allowable payment.
affordableLoanAmount = 0;
}
} else if (monthlyRateFactor === 0 && estimatedPitiRatioPerMonth > 0) { // Case where rate is 0%
var numeratorForLoanAmount = maxPrincipalInterestAndTaxesInsurance – (downPayment * estimatedPitiRatioPerMonth);
if (numeratorForLoanAmount > 0) {
affordableLoanAmount = numeratorForLoanAmount / estimatedPitiRatioPerMonth;
} else {
affordableLoanAmount = 0;
}
}
var estimatedMaxHomePrice = affordableLoanAmount + downPayment;
// Final check: calculate the PITI for the estimated home price and loan amount.
var estimatedMonthlyTaxesInsurance = estimatedMaxHomePrice * estimatedPitiRatioPerMonth;
var estimatedMonthlyPrincipalInterest = 0;
if (monthlyInterestRate > 0 && numberOfPayments > 0) {
estimatedMonthlyPrincipalInterest = affordableLoanAmount * monthlyRateFactor;
} else if (monthlyInterestRate === 0 && numberOfPayments > 0) {
estimatedMonthlyPrincipalInterest = affordableLoanAmount / numberOfPayments; // Simple division for 0% interest
}
var totalEstimatedMonthlyHousingCost = estimatedMonthlyPrincipalInterest + estimatedMonthlyTaxesInsurance;
if (estimatedMaxHomePrice > 0 && totalEstimatedMonthlyHousingCost <= maxTotalObligations) {
resultDiv.innerHTML =
"