Use this calculator to estimate how much house you can afford based on your income, debts, and down payment. Remember, this is an estimate and your actual loan approval will depend on lender specific criteria.
.calculator-container {
font-family: sans-serif;
border: 1px solid #ddd;
padding: 20px;
border-radius: 8px;
max-width: 500px;
margin: 20px auto;
background-color: #f9f9f9;
}
.calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 15px;
}
.calculator-container p {
font-size: 0.9em;
color: #555;
text-align: center;
margin-bottom: 20px;
}
.input-section {
margin-bottom: 20px;
}
.input-section label {
display: block;
margin-bottom: 8px;
color: #444;
font-weight: bold;
}
.input-section input[type="number"] {
width: calc(100% – 20px);
padding: 10px;
margin-bottom: 15px;
border: 1px solid #ccc;
border-radius: 4px;
box-sizing: border-box;
}
button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 5px;
cursor: pointer;
font-size: 1.1em;
transition: background-color 0.3s ease;
}
button:hover {
background-color: #0056b3;
}
.result-section {
margin-top: 25px;
padding: 15px;
background-color: #e9ecef;
border: 1px solid #ced4da;
border-radius: 5px;
text-align: center;
font-size: 1.1em;
color: #333;
}
.result-section strong {
color: #28a745;
}
function calculateMortgageAffordability() {
var annualIncome = parseFloat(document.getElementById("annualIncome").value);
var monthlyDebt = parseFloat(document.getElementById("monthlyDebt").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTerm = parseFloat(document.getElementById("loanTerm").value);
var resultElement = document.getElementById("result");
resultElement.innerHTML = ""; // Clear previous results
// Validate inputs
if (isNaN(annualIncome) || isNaN(monthlyDebt) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTerm) ||
annualIncome < 0 || monthlyDebt < 0 || downPayment < 0 || interestRate < 0 || loanTerm <= 0) {
resultElement.innerHTML = "Please enter valid positive numbers for all fields.";
return;
}
// Lender typically use Debt-to-Income (DTI) ratios.
// Front-end DTI (Housing Costs / Gross Income) around 28%
// Back-end DTI (Total Debt / Gross Income) around 36%
// We'll use these as rough guides to estimate maximum housing payment and thus maximum loan.
var grossMonthlyIncome = annualIncome / 12;
// Calculate maximum housing payment based on 28% DTI for housing
var maxHousingPayment = grossMonthlyIncome * 0.28;
// Calculate maximum total debt payment based on 36% DTI for total debt
var maxTotalDebtPayment = grossMonthlyIncome * 0.36;
// Calculate maximum allowable mortgage payment (PITI)
var maxMortgagePayment = maxTotalDebtPayment – monthlyDebt;
// Ensure the calculated max mortgage payment is not negative and not exceeding the housing DTI limit
if (maxMortgagePayment maxHousingPayment) {
maxMortgagePayment = maxHousingPayment;
}
// If the maximum allowable mortgage payment is zero or less, the user can't afford a mortgage.
if (maxMortgagePayment <= 0) {
resultElement.innerHTML = "Based on your income and existing debts, you may not be able to afford a mortgage at this time.";
return;
}
// Now, estimate the maximum loan amount based on the maximum mortgage payment
// We need to approximate PITI (Principal, Interest, Taxes, Insurance).
// For simplicity, we'll assume taxes and insurance add about 1% of the loan value annually, or 0.0833% monthly.
// This is a significant simplification. A real calculator would have separate inputs for these.
var estimatedAnnualTaxesAndInsuranceRate = 0.01; // 1% of loan value annually
var monthlyTaxesAndInsuranceRate = estimatedAnnualTaxesAndInsuranceRate / 12;
var monthlyInterestRate = (interestRate / 100) / 12;
var numberOfPayments = loanTerm * 12;
var maxLoanAmount = 0;
// If interest rate is very close to zero, use a simplified calculation to avoid division by zero.
if (monthlyInterestRate < 0.00001) {
maxLoanAmount = maxMortgagePayment / (1 + monthlyTaxesAndInsuranceRate);
} else {
// 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 = Number of Payments
// We need to solve for P: P = M [ (1 + i)^n – 1] / [ i(1 + i)^n ]
var factor = Math.pow(1 + monthlyInterestRate, numberOfPayments);
var principalPortion = (factor – 1) / (monthlyInterestRate * factor);
// Calculate the maximum loan principal the payment can support, after accounting for taxes and insurance
// maxMortgagePayment = P + P * monthlyTaxesAndInsuranceRate (simplified for calculation)
// maxMortgagePayment = P * (1 + monthlyTaxesAndInsuranceRate)
// P = maxMortgagePayment / (1 + monthlyTaxesAndInsuranceRate) <- This is NOT how it works.
// Correct approach: maxMortgagePayment = (Principal + Interest) + Taxes + Insurance
// var P_and_I be the principal and interest portion of the payment.
// P_and_I = maxMortgagePayment – (Estimated Taxes and Insurance)
// Estimated Taxes and Insurance = P * monthlyTaxesAndInsuranceRate
// So, P_and_I = P * (1 + monthlyTaxesAndInsuranceRate) ? No. This is getting complicated.
// A better approach:
// var M_total be the maxMortgagePayment.
// M_total = M_pi + M_ti (Monthly Principal & Interest + Monthly Taxes & Insurance)
// M_pi = P * [ i(1 + i)^n ] / [ (1 + i)^n – 1]
// M_ti = P * monthlyTaxesAndInsuranceRate (Approximation)
// M_total = P * ([ i(1 + i)^n ] / [ (1 + i)^n – 1] + monthlyTaxesAndInsuranceRate)
// P = M_total / ([ i(1 + i)^n ] / [ (1 + i)^n – 1] + monthlyTaxesAndInsuranceRate)
var numerator = Math.pow(1 + monthlyInterestRate, numberOfPayments) – 1;
var denominator = monthlyInterestRate * Math.pow(1 + monthlyInterestRate, numberOfPayments);
var principalAndInterestFactor = numerator / denominator;
maxLoanAmount = maxMortgagePayment / (principalAndInterestFactor + monthlyTaxesAndInsuranceRate);
}
// The maximum affordable home price is the maximum loan amount plus the down payment
var maxAffordablePrice = maxLoanAmount + downPayment;
// Format results
var formattedMaxLoan = maxLoanAmount.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxAffordablePrice = maxAffordablePrice.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
var formattedMaxMortgagePayment = maxMortgagePayment.toLocaleString(undefined, { style: 'currency', currency: 'USD' });
resultElement.innerHTML = "
Estimated Affordability
" +
"Maximum Estimated Monthly Mortgage Payment (PITI): " + formattedMaxMortgagePayment + "" +
"Estimated Maximum Loan Amount: " + formattedMaxLoan + "" +
"Estimated Maximum Affordable Home Price (with down payment): " + formattedMaxAffordablePrice + "" +
"Note: This calculator uses general DTI ratios (28% housing, 36% total debt) and a simplified estimate for taxes and insurance (1% annually). Actual loan amounts and home prices may vary significantly based on lender policies, credit score, exact property taxes, homeowner's insurance, PMI, and other fees.";
}