Mortgage Affordability Calculator
This calculator helps you estimate how much home you can afford based on your income, debts, and desired mortgage terms. Understanding your borrowing capacity is a crucial first step in the home-buying process. It allows you to set realistic expectations and focus your house search on properties within your budget.
function calculateMortgageAffordability() {
var grossMonthlyIncome = parseFloat(document.getElementById("grossMonthlyIncome").value);
var monthlyDebtPayments = parseFloat(document.getElementById("monthlyDebtPayments").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var annualInterestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseInt(document.getElementById("loanTermYears").value);
var resultElement = document.getElementById("result");
resultElement.innerHTML = ""; // Clear previous results
// Input validation
if (isNaN(grossMonthlyIncome) || grossMonthlyIncome <= 0 ||
isNaN(monthlyDebtPayments) || monthlyDebtPayments < 0 ||
isNaN(downPayment) || downPayment < 0 ||
isNaN(annualInterestRate) || annualInterestRate <= 0 ||
isNaN(loanTermYears) || loanTermYears <= 0) {
resultElement.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Debt-to-Income Ratio (DTI) guidelines (common lender limits)
var maxDTIFrontEnd = 0.28; // Typically around 28% for housing costs
var maxDTIBackEnd = 0.36; // Typically around 36% for total debt
// Calculate maximum allowed monthly housing payment (Principal, Interest, Taxes, Insurance – PITI)
var maxMonthlyHousingPayment = (grossMonthlyIncome * maxDTIFrontEnd);
// Calculate maximum total monthly debt payments allowed
var maxTotalMonthlyDebt = (grossMonthlyIncome * maxDTIBackEnd);
// Calculate the maximum allowable monthly mortgage payment (P&I only)
// This is the maximum housing payment minus property taxes and homeowners insurance (estimated)
// We'll use a simplified approach here for P&I, assuming taxes/insurance are a portion of the max housing payment.
// A more complex calculator would ask for tax/insurance estimates.
var estimatedMonthlyTaxesAndInsurance = (grossMonthlyIncome * 0.01); // A rough estimate, could be 1% of home value annually / 12
var maxMonthlyMortgagePayment = maxMonthlyHousingPayment – estimatedMonthlyTaxesAndInsurance;
// Ensure maxMonthlyMortgagePayment is not negative
if (maxMonthlyMortgagePayment 0) {
maxLoanAmount = maxMonthlyMortgagePayment * (1 – Math.pow(1 + monthlyInterestRate, -numberOfPayments)) / monthlyInterestRate;
} else {
// Handle 0% interest rate scenario
maxLoanAmount = maxMonthlyMortgagePayment * numberOfPayments;
}
// Adjust maxLoanAmount based on total debt limits if applicable
var maxPossibleTotalDebtPayment = maxTotalMonthlyDebt – monthlyDebtPayments;
var maxPossibleMortgagePAndI = Math.max(0, maxPossibleTotalDebtPayment); // Ensure it's not negative
// If the P&I limit calculated from total debt is lower than the P&I limit from housing costs, use the lower one.
if (maxPossibleMortgagePAndI < maxLoanAmount * monthlyInterestRate / (1 – Math.pow(1 + monthlyInterestRate, -numberOfPayments))) {
// This part is tricky to back-calculate precisely without knowing the exact P&I amount.
// For simplicity, we'll consider if the *total debt payment capacity* allows for this loan.
// A more robust calculation would iteratively find the loan amount.
// For this example, we'll focus on the DTI of 36% as the primary constraint if it's more restrictive.
// If maxPossibleMortgagePAndI is the limiting factor, the affordable loan amount would be
// calculated based on this P&I.
// For simplicity in this calculator, we'll present both limits and the user can see which is more restrictive.
}
// Calculate estimated maximum home price
var estimatedMaxHomePrice = maxLoanAmount + downPayment;
// Format results
var formattedMaxHomePrice = estimatedMaxHomePrice.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxLoanAmount = maxLoanAmount.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxMonthlyHousingPayment = maxMonthlyHousingPayment.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxTotalMonthlyDebt = maxTotalMonthlyDebt.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxMonthlyMortgagePayment = maxMonthlyMortgagePayment.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
resultElement.innerHTML =
"
Your Estimated Affordability:
" +
"
Estimated Maximum Home Price: " + formattedMaxHomePrice + "" +
"
Estimated Maximum Loan Amount: " + formattedMaxLoanAmount + "" +
"This is based on common lender guidelines:" +
"
" +
"- Max Monthly Housing Payment (PITI): " + formattedMaxMonthlyHousingPayment + " (typically ~28% of gross income)
" +
"- Max Total Monthly Debt (including PITI): " + formattedMaxTotalMonthlyDebt + " (typically ~36% of gross income)
" +
"- Estimated Max Monthly P&I Payment: " + formattedMaxMonthlyMortgagePayment + "
" +
"
" +
"
Disclaimer: This is an estimate only. Actual loan approval depends on lender policies, credit score, loan type, and other factors. Consult with a mortgage professional for personalized advice.";
}
.calculator-container {
font-family: sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
box-shadow: 0 2px 5px rgba(0,0,0,0.1);
background-color: #fff;
}
.calculator-title {
text-align: center;
color: #333;
margin-bottom: 15px;
}
.calculator-description {
color: #555;
line-height: 1.6;
margin-bottom: 25px;
text-align: justify;
}
.calculator-form .form-group {
margin-bottom: 15px;
display: flex;
flex-direction: column;
}
.calculator-form label {
margin-bottom: 5px;
font-weight: bold;
color: #444;
}
.calculator-form input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1em;
box-sizing: border-box; /* Ensures padding doesn't affect width */
}
.calculator-button {
display: block;
width: 100%;
padding: 12px;
background-color: #007bff;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1em;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 30px;
padding: 15px;
border: 1px solid #e0e0e0;
border-radius: 5px;
background-color: #f9f9f9;
}
.calculator-result h3 {
color: #007bff;
margin-top: 0;
margin-bottom: 15px;
}
.calculator-result p {
margin-bottom: 10px;
color: #333;
line-height: 1.5;
}
.calculator-result ul {
margin-top: 10px;
padding-left: 20px;
color: #555;
}
.calculator-result li {
margin-bottom: 5px;
}
.calculator-result .note {
font-size: 0.9em;
color: #666;
margin-top: 15px;
margin-bottom: 5px;
}
.calculator-result .disclaimer {
font-size: 0.85em;
color: #888;
border-top: 1px dashed #ccc;
padding-top: 10px;
margin-top: 15px;
text-align: center;
}
.calculator-result .error {
color: red;
font-weight: bold;
}