#affordability-calculator-wrapper {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e0e0e0;
border-radius: 12px;
background-color: #ffffff;
color: #333;
box-shadow: 0 4px 15px rgba(0,0,0,0.05);
}
.calc-header {
text-align: center;
margin-bottom: 25px;
}
.calc-header h2 {
color: #1a237e;
margin-bottom: 10px;
font-size: 28px;
}
.input-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
.input-group {
display: flex;
flex-direction: column;
}
.input-group label {
font-weight: 600;
margin-bottom: 8px;
font-size: 14px;
color: #555;
}
.input-group input, .input-group select {
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 16px;
}
.calc-btn {
grid-column: span 2;
background-color: #1a237e;
color: white;
padding: 15px;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
margin-top: 10px;
transition: background 0.3s;
}
.calc-btn:hover {
background-color: #0d47a1;
}
#affordability-result {
margin-top: 30px;
padding: 20px;
background-color: #f8f9fa;
border-radius: 8px;
border-left: 5px solid #1a237e;
display: none;
}
.result-title {
font-size: 16px;
color: #666;
margin-bottom: 5px;
}
.result-value {
font-size: 32px;
font-weight: 800;
color: #1a237e;
margin-bottom: 15px;
}
.result-details {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 10px;
font-size: 14px;
}
.detail-item span {
font-weight: bold;
color: #333;
}
.article-section {
margin-top: 40px;
line-height: 1.6;
color: #444;
}
.article-section h3 {
color: #1a237e;
margin-top: 25px;
}
@media (max-width: 600px) {
.input-grid { grid-template-columns: 1fr; }
.calc-btn { grid-column: span 1; }
}
Estimated Home Buying Power:
$0
Monthly P&I: $0
Total Loan Amount: $0
Income Used: $0/mo
Debt Allowance: $0/mo
How Is Mortgage Affordability Calculated?
Mortgage affordability is primarily determined by your Debt-to-Income (DTI) ratio. Lenders generally look at two figures: your front-end ratio (the percentage of income going to housing) and your back-end ratio (the percentage of income going to all debts). Most standard loan programs prefer a back-end DTI of 43% or lower.
This calculator uses your gross annual income, subtracts your existing monthly obligations, and determines the maximum monthly principal and interest payment you can sustain. It then uses the current interest rate and loan term to reverse-calculate the total loan amount you qualify for.
Key Factors Affecting Your Buying Power
- Interest Rates: Even a 1% shift in interest rates can change your buying power by tens of thousands of dollars.
- Down Payment: A larger down payment reduces the loan-to-value ratio, often leading to better rates and eliminating the need for Private Mortgage Insurance (PMI).
- Monthly Debts: High car payments or student loan balances directly subtract from the amount you can put toward a mortgage.
- Property Taxes & Insurance: While this calculator focuses on Principal and Interest, remember that taxes and insurance typically add 15-25% to your total monthly housing cost.
Example Scenario
If you earn $100,000 annually, your gross monthly income is $8,333. With a standard 43% DTI limit, your total debt ceiling is $3,583. If you already have $500 in car and credit card payments, you have $3,083 left for your mortgage payment. At a 6.5% interest rate on a 30-year term, this could potentially support a home price of over $500,000 depending on your down payment.
function calculateAffordability() {
var grossIncome = parseFloat(document.getElementById("grossIncome").value);
var downPayment = parseFloat(document.getElementById("downPayment").value);
var monthlyDebts = parseFloat(document.getElementById("monthlyDebts").value);
var interestRate = parseFloat(document.getElementById("interestRate").value);
var loanTermYears = parseInt(document.getElementById("loanTerm").value);
var dtiLimit = parseFloat(document.getElementById("dtiRatio").value) / 100;
if (isNaN(grossIncome) || isNaN(downPayment) || isNaN(monthlyDebts) || isNaN(interestRate)) {
alert("Please enter valid numeric values.");
return;
}
// 1. Calculate Monthly Gross Income
var monthlyGross = grossIncome / 12;
// 2. Calculate Maximum Total Monthly Debt Allowed
var maxTotalMonthlyDebt = monthlyGross * dtiLimit;
// 3. Subtract existing debts to find available P&I (Principal & Interest)
// Note: In reality, taxes and insurance (TI) are also in this, but for buying power estimation,
// we focus on the loan capacity. We'll reserve 20% of the available payment for Taxes/Insurance.
var availableForPITI = maxTotalMonthlyDebt – monthlyDebts;
// Safety check for negative values
if (availableForPITI <= 0) {
document.getElementById("maxHomePrice").innerHTML = "Insufficient Income";
document.getElementById("affordability-result").style.display = "block";
return;
}
// Estimate 25% of the housing budget goes to Taxes and Insurance
var availableForPI = availableForPITI * 0.80;
// 4. Calculate Loan Amount based on P&I
// Formula: P = M / [i(1+i)^n / ((1+i)^n – 1)]
// where M is monthly payment, i is monthly interest, n is total months
var monthlyRate = (interestRate / 100) / 12;
var totalMonths = loanTermYears * 12;
var loanAmount = 0;
if (monthlyRate === 0) {
loanAmount = availableForPI * totalMonths;
} else {
var numerator = Math.pow(1 + monthlyRate, totalMonths) – 1;
var denominator = monthlyRate * Math.pow(1 + monthlyRate, totalMonths);
loanAmount = availableForPI * (numerator / denominator);
}
// 5. Total Home Price = Loan Amount + Down Payment
var maxHomePrice = loanAmount + downPayment;
// Format results
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
maximumFractionDigits: 0
});
document.getElementById("maxHomePrice").innerHTML = formatter.format(maxHomePrice);
document.getElementById("monthlyPI").innerHTML = formatter.format(availableForPI);
document.getElementById("totalLoan").innerHTML = formatter.format(loanAmount);
document.getElementById("incomeUsed").innerHTML = formatter.format(monthlyGross);
document.getElementById("debtAllowance").innerHTML = formatter.format(maxTotalMonthlyDebt);
document.getElementById("affordability-result").style.display = "block";
}