Use this calculator to estimate how much you can afford to borrow for a mortgage. This calculation takes into account your income, debts, and estimated monthly housing expenses.
function calculateMortgageAffordability() {
var grossMonthlyIncome = parseFloat(document.getElementById("grossMonthlyIncome").value);
var monthlyDebtPayments = parseFloat(document.getElementById("monthlyDebtPayments").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var propertyTaxesAnnual = parseFloat(document.getElementById("propertyTaxesAnnual").value);
var homeInsuranceAnnual = parseFloat(document.getElementById("homeInsuranceAnnual").value);
var pmiAnnual = parseFloat(document.getElementById("pmiAnnual").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(interestRate) || interestRate <= 0 ||
isNaN(loanTerm) || loanTerm <= 0 ||
isNaN(propertyTaxesAnnual) || propertyTaxesAnnual < 0 ||
isNaN(homeInsuranceAnnual) || homeInsuranceAnnual < 0 ||
isNaN(pmiAnnual) || pmiAnnual < 0) {
resultElement.innerHTML = "Please enter valid numbers for all fields.";
return;
}
// Lender Debt-to-Income (DTI) Ratios – common guidelines
var frontEndDTI_max = 0.28; // Housing expenses (PITI) / Gross Monthly Income
var backEndDTI_max = 0.36; // Total Debt Payments (including PITI) / Gross Monthly Income
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfMonths = loanTerm * 12;
var monthlyPropertyTaxes = propertyTaxesAnnual / 12;
var monthlyHomeInsurance = homeInsuranceAnnual / 12;
var monthlyPMI = pmiAnnual / 12;
// Calculate maximum housing payment (PITI) based on front-end DTI
var maxHousingPayment_frontend = grossMonthlyIncome * frontEndDTI_max;
// Calculate maximum total debt payment based on back-end DTI
var maxTotalDebtPayment_backend = grossMonthlyIncome * backEndDTI_max;
// Calculate the maximum allowable monthly mortgage payment (Principal & Interest – PI)
// First, determine the maximum allowed monthly PITI
var maxPITI = Math.min(maxHousingPayment_frontend, maxTotalDebtPayment_backend – monthlyDebtPayments);
// Ensure maxPITI is not negative
if (maxPITI < 0) {
resultElement.innerHTML = "Based on your debt obligations, you may not qualify for a mortgage at this time.";
return;
}
// Now, subtract the estimated monthly taxes, insurance, and PMI from the maximum PITI to find the maximum PI payment
var maxPI = maxPITI – monthlyPropertyTaxes – monthlyHomeInsurance – monthlyPMI;
// Ensure maxPI is not negative
if (maxPI 0 && numberOfMonths > 0) {
// Formula for loan amount given payment: L = P * [1 – (1 + r)^-n] / r
maxLoanAmount = maxPI * (1 – Math.pow(1 + monthlyInterestRate, -numberOfMonths)) / monthlyInterestRate;
} else if (maxPI > 0) { // Handle case of 0% interest rate (unlikely for mortgage but for logic completeness)
maxLoanAmount = maxPI * numberOfMonths;
}
var affordableHomePrice = maxLoanAmount + downPayment;
resultElement.innerHTML =
"Estimated Maximum Affordable Home Price:$" + affordableHomePrice.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,') + "" +
"Disclaimer: This is an estimate based on common lender guidelines. Your actual loan approval may vary based on your credit score, lender specifics, and other factors.";
}
.calculator-container {
font-family: Arial, sans-serif;
max-width: 600px;
margin: 20px auto;
padding: 20px;
border: 1px solid #ddd;
border-radius: 8px;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 20px;
}
.calculator-container p {
font-size: 0.95em;
line-height: 1.5;
color: #555;
margin-bottom: 20px;
}
.calculator-inputs {
display: grid;
grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
gap: 15px;
margin-bottom: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
margin-bottom: 5px;
font-weight: bold;
color: #444;
font-size: 0.9em;
}
.input-group input[type="number"] {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 1em;
box-sizing: border-box; /* Include padding and border in the element's total width and height */
}
.calculator-container button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 5px;
font-size: 1.1em;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-container button:hover {
background-color: #0056b3;
}
.calculator-result {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 5px;
text-align: center;
}
.calculator-result p {
margin-bottom: 10px;
font-size: 1.1em;
color: #333;
}
.calculator-result span {
font-size: 1.3em;
}
.calculator-result em {
font-size: 0.85em;
color: #6c757d;
display: block;
margin-top: 10px;
}