Understanding how much house you can afford is a crucial first step in the home-buying process. A mortgage affordability calculator helps you estimate the maximum loan amount you might qualify for, based on your income, debts, and estimated interest rates. This calculator considers several key factors to provide a realistic estimate.
Key Factors:
Gross Monthly Income: This is your total income before taxes and deductions. Lenders use this to gauge your ability to repay a loan.
Existing Monthly Debt Payments: This includes credit card payments, car loans, student loans, and any other recurring debt obligations. Lenders want to see that your new mortgage payment, combined with your existing debts, doesn't exceed a certain percentage of your income.
Estimated Interest Rate: This is the annual interest rate you expect to pay on your mortgage. Higher interest rates mean higher monthly payments for the same loan amount.
Loan Term (Years): The length of time over which you'll repay the loan (e.g., 15, 30 years). A shorter term usually means higher monthly payments but less interest paid overall.
Down Payment: The upfront amount of money you pay towards the purchase price of the home. A larger down payment reduces the loan amount needed.
Lenders typically use debt-to-income ratios (DTI) to assess affordability. A common guideline is that your total monthly debt payments (including the estimated new mortgage payment) should not exceed 43% of your gross monthly income. This calculator provides an estimate based on these principles.
Mortgage Affordability Calculator
function calculateMortgageAffordability() {
var grossMonthlyIncome = parseFloat(document.getElementById("grossMonthlyIncome").value);
var existingMonthlyDebt = parseFloat(document.getElementById("existingMonthlyDebt").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseFloat(document.getElementById("loanTermYears").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(grossMonthlyIncome) || isNaN(existingMonthlyDebt) || isNaN(interestRate) || isNaN(loanTermYears) || isNaN(downPayment)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (grossMonthlyIncome <= 0 || existingMonthlyDebt < 0 || interestRate < 0 || loanTermYears <= 0 || downPayment < 0) {
resultDiv.innerHTML = "Please enter valid positive numbers (or zero for debt/down payment).";
return;
}
// Assuming a maximum DTI of 43% for total debt payments (including PITI)
var maxTotalMonthlyPayment = grossMonthlyIncome * 0.43;
var maxMortgagePayment = maxTotalMonthlyPayment – existingMonthlyDebt;
if (maxMortgagePayment <= 0) {
resultDiv.innerHTML = "Based on your income and existing debts, you may not be able to afford a mortgage payment. Consider increasing income or reducing debt.";
return;
}
// Mortgage payment formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Where:
// M = Monthly payment
// P = Principal loan amount
// i = Monthly interest rate
// n = Total number of payments (loan term in months)
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTermYears * 12;
// We need to find the maximum principal (P) based on the maximum mortgage payment
// Rearranging the formula: P = M * [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var maxPrincipal = maxMortgagePayment * (Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1) / (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments));
// The maximum affordable house price is the maximum principal plus the down payment
var maxHousePrice = maxPrincipal + downPayment;
// Format results for display
var formattedMaxHousePrice = maxHousePrice.toLocaleString('en-US', { style: 'currency', currency: 'USD' });
var formattedMaxPrincipal = maxPrincipal.toLocaleString('en-US', { style: 'currency', currency: 'USD' });
var formattedMaxMortgagePayment = maxMortgagePayment.toLocaleString('en-US', { style: 'currency', currency: 'USD' });
resultDiv.innerHTML =
"Estimated Maximum House Price You Can Afford: " + formattedMaxHousePrice + "" +
"(This includes your down payment of " + downPayment.toLocaleString('en-US', { style: 'currency', currency: 'USD' }) + ")" +
"Estimated Maximum Loan Amount: " + formattedMaxPrincipal + "" +
"Estimated Maximum Monthly Mortgage Payment (Principal & Interest, plus estimated taxes/insurance): " + formattedMaxMortgagePayment + "" +
"Note: This is an estimate. Actual loan approval depends on lender's specific criteria, credit score, property taxes, homeowner's insurance, PMI (if applicable), and other factors.";
}
.calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ccc;
border-radius: 8px;
background-color: #f9f9f9;
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