Understanding how much you can afford for a mortgage is a crucial first step in your home-buying journey. This calculator helps you estimate your maximum affordable mortgage amount based on your income, debts, and desired monthly payment. It's important to note that this is an estimation and lenders will consider many other factors, including your credit score, down payment, and loan terms.
.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);
}
.calculator-container h2 {
text-align: center;
margin-bottom: 15px;
color: #333;
}
.calculator-container p {
margin-bottom: 20px;
line-height: 1.5;
color: #555;
text-align: justify;
}
.input-section label {
display: block;
margin-bottom: 8px;
font-weight: bold;
color: #444;
}
.input-section input {
width: calc(100% – 16px);
padding: 10px;
margin-bottom: 15px;
border: 1px solid #ccc;
border-radius: 4px;
box-sizing: border-box;
}
.calculator-container button {
display: block;
width: 100%;
padding: 12px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 16px;
cursor: pointer;
transition: background-color 0.3s ease;
}
.calculator-container button:hover {
background-color: #0056b3;
}
#result {
margin-top: 20px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 4px;
text-align: center;
font-size: 1.1em;
color: #212529;
}
#result strong {
color: #0056b3;
}
function calculateMortgageAffordability() {
var monthlyIncome = parseFloat(document.getElementById("monthlyIncome").value);
var existingMonthlyDebt = parseFloat(document.getElementById("existingMonthlyDebt").value);
var desiredMonthlyPayment = parseFloat(document.getElementById("desiredMonthlyPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(monthlyIncome) || isNaN(existingMonthlyDebt) || isNaN(desiredMonthlyPayment) || isNaN(interestRate) || isNaN(loanTerm)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
// General rule of thumb: Debt-to-Income Ratio (DTI)
// Lenders typically prefer a total DTI (including housing) of 36% or less,
// and a housing DTI (PITI) of 28% or less.
// We'll use the desiredMonthlyPayment as the PITI and see if it fits within
// the income, considering existing debt.
// Calculate maximum allowed total monthly debt based on desired PITI and DTI guidelines
var maxHousingPaymentPercentage = 0.28; // Example: 28% of gross income for housing
var maxTotalDebtPercentage = 0.36; // Example: 36% of gross income for all debt
var maxAllowedHousingPayment = monthlyIncome * maxHousingPaymentPercentage;
var maxAllowedTotalDebt = monthlyIncome * maxTotalDebtPercentage;
var affordabilityMessage = "";
if (desiredMonthlyPayment > maxAllowedHousingPayment) {
affordabilityMessage += "Based on the 28% rule, your desired monthly payment of $" + desiredMonthlyPayment.toFixed(2) + " might be too high for your monthly income of $" + monthlyIncome.toFixed(2) + " (max recommended housing payment: $" + maxAllowedHousingPayment.toFixed(2) + "). ";
}
var remainingIncomeForMortgage = monthlyIncome – existingMonthlyDebt;
var maxAffordableMortgagePaymentPossible = remainingIncomeForMortgage – existingMonthlyDebt; // This is a simplification to check if existing debt leaves room for PITI
if (desiredMonthlyPayment > maxAllowedTotalDebt – existingMonthlyDebt) {
affordabilityMessage += "Considering your existing monthly debt of $" + existingMonthlyDebt.toFixed(2) + ", your desired total monthly debt payment (including mortgage) of $" + (desiredMonthlyPayment + existingMonthlyDebt).toFixed(2) + " might exceed the recommended 36% DTI of $" + maxAllowedTotalDebt.toFixed(2) + ". ";
}
// Further calculation to estimate loan amount based on desired payment, rate, and term
// Formula for monthly mortgage payment (M): M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// Where:
// P = Principal loan amount
// i = Monthly interest rate (annual rate / 12)
// n = Total number of payments (loan term in years * 12)
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var estimatedLoanAmount = 0;
if (monthlyInterestRate > 0 && numberOfPayments > 0) {
// Rearranging the formula to solve for P (Principal):
// P = M [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var numerator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
if (denominator > 0) {
estimatedLoanAmount = desiredMonthlyPayment * (numerator / denominator);
}
} else if (desiredMonthlyPayment > 0 && monthlyInterestRate === 0) {
// Handle zero interest rate case (simple division)
estimatedLoanAmount = desiredMonthlyPayment * numberOfPayments;
}
if (estimatedLoanAmount > 0) {
var resultHtml = "Your estimated maximum affordable loan amount is: $" + estimatedLoanAmount.toFixed(2) + ".";
resultHtml += "This is based on a target monthly payment of $" + desiredMonthlyPayment.toFixed(2) + ", an interest rate of " + interestRate + "%, and a loan term of " + loanTerm + " years.";
resultHtml += affordabilityMessage;
resultHtml += "Disclaimer: This is an estimation only. Actual loan approval depends on lender's criteria, credit score, down payment, and other financial factors.";
resultDiv.innerHTML = resultHtml;
} else {
resultDiv.innerHTML = "Could not calculate affordable loan amount with the provided inputs. Please check your values.";
}
}