House Affordability Calculator
/* Global Styles */
body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
background-color: #f9f9f9;
}
/* Calculator Container */
.calculator-widget {
background: #fff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 4px 20px rgba(0,0,0,0.08);
margin-bottom: 40px;
border: 1px solid #e1e1e1;
}
.calculator-title {
text-align: center;
margin-bottom: 25px;
color: #2c3e50;
font-size: 24px;
font-weight: 700;
}
/* Form Layout */
.form-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 600px) {
.form-grid {
grid-template-columns: 1fr;
}
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
font-size: 14px;
color: #555;
}
.input-wrapper {
position: relative;
display: flex;
align-items: center;
}
.input-wrapper span {
position: absolute;
left: 12px;
color: #777;
}
.input-wrapper input {
width: 100%;
padding: 12px 12px 12px 30px; /* Space for symbol */
border: 1px solid #ddd;
border-radius: 6px;
font-size: 16px;
transition: border-color 0.3s;
}
.input-wrapper input:focus {
border-color: #3498db;
outline: none;
box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.1);
}
.input-wrapper.percent input {
padding-left: 12px;
padding-right: 30px;
}
.input-wrapper.percent span {
left: auto;
right: 12px;
}
.calc-btn {
width: 100%;
background-color: #2ecc71;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 6px;
cursor: pointer;
margin-top: 20px;
transition: background-color 0.2s;
}
.calc-btn:hover {
background-color: #27ae60;
}
/* Results Section */
.results-container {
margin-top: 30px;
background-color: #f8fbfd;
border: 1px solid #bee3f8;
border-radius: 8px;
padding: 20px;
display: none; /* Hidden by default */
}
.main-result {
text-align: center;
margin-bottom: 20px;
border-bottom: 1px solid #e1e1e1;
padding-bottom: 20px;
}
.main-result h3 {
margin: 0;
font-size: 16px;
color: #666;
text-transform: uppercase;
letter-spacing: 1px;
}
.main-result .price-tag {
font-size: 42px;
font-weight: 800;
color: #2c3e50;
margin: 10px 0;
}
.breakdown-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 15px;
}
.breakdown-item {
background: white;
padding: 10px;
border-radius: 6px;
border: 1px solid #eee;
}
.breakdown-label {
font-size: 13px;
color: #777;
}
.breakdown-value {
font-size: 16px;
font-weight: 600;
color: #333;
}
.error-msg {
color: #e74c3c;
text-align: center;
margin-top: 10px;
display: none;
}
/* Content Styling */
.content-section {
background: #fff;
padding: 30px;
border-radius: 12px;
box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}
.content-section h2 {
color: #2c3e50;
border-bottom: 2px solid #2ecc71;
padding-bottom: 10px;
margin-top: 0;
}
.content-section h3 {
color: #34495e;
margin-top: 25px;
}
.content-section p, .content-section li {
color: #555;
font-size: 16px;
}
.highlight-box {
background-color: #fff9c4;
padding: 15px;
border-left: 4px solid #fbc02d;
margin: 20px 0;
}
How Much House Can I Afford?
Determining your home buying budget is the most critical first step in the real estate journey. This House Affordability Calculator uses the standard "28/36 rule" favored by most financial lenders to give you a realistic estimate of your purchasing power.
Understanding the 28/36 Rule
Mortgage lenders look at two primary ratios to decide how much money they are willing to lend you:
- Front-End Ratio (28%): Your monthly housing costs (principal, interest, taxes, insurance, and HOA) should not exceed 28% of your gross monthly income.
- Back-End Ratio (36%): Your total monthly debt payments (housing costs + car loans, student loans, credit cards) should not exceed 36% of your gross monthly income.
Our calculator computes both scenarios and uses the lower number to ensure you stay within a safe financial limit.
Pro Tip: Don't forget closing costs! Typically 2-5% of the purchase price, these are separate from your down payment. Our calculator estimates these for you in the results breakdown.
Key Factors Affecting Your Affordability
Several variables can significantly change your buying power:
1. Debt-to-Income (DTI) Ratio
High monthly debts (like a $500 car payment) drastically reduce your mortgage capability because they eat into your "Back-End" allowance. Paying off a small loan before applying for a mortgage can sometimes increase your buying power by tens of thousands of dollars.
2. Interest Rates
Even a 1% difference in interest rates can change your monthly payment by hundreds of dollars. As rates rise, your maximum affordable home price decreases because more of your monthly payment goes toward interest rather than principal.
3. Property Taxes
Property taxes vary wildly by location. In some areas, they may be 0.5% of the home value, while in others, they can exceed 2.5%. Since taxes are part of your monthly PITI (Principal, Interest, Taxes, Insurance) payment, high taxes reduce the amount of loan you can afford.
How to Use This Calculator
- Gross Income: Enter your total pre-tax income for the year. Include co-borrower income if applicable.
- Monthly Debts: Sum up minimum payments for credit cards, auto loans, and student loans. Do not include utilities or groceries.
- Down Payment: The cash you have on hand. Note that a higher down payment reduces the loan amount and eliminates Private Mortgage Insurance (PMI) if it's over 20%.
- Interest Rate: Check current market rates for a 30-year fixed mortgage.
function calculateAffordability() {
// 1. Get Inputs
var annualIncome = parseFloat(document.getElementById('annualIncome').value);
var downPayment = parseFloat(document.getElementById('downPayment').value) || 0;
var monthlyDebt = parseFloat(document.getElementById('monthlyDebt').value) || 0;
var interestRate = parseFloat(document.getElementById('interestRate').value);
var loanTermYears = parseFloat(document.getElementById('loanTerm').value) || 30;
var taxRate = parseFloat(document.getElementById('propertyTax').value) || 0;
var annualInsurance = parseFloat(document.getElementById('homeInsurance').value) || 0;
var monthlyHOA = parseFloat(document.getElementById('hoaFees').value) || 0;
// Validation
var errorDiv = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('results');
if (isNaN(annualIncome) || annualIncome <= 0 || isNaN(interestRate)) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
errorDiv.style.display = 'none';
resultsDiv.style.display = 'block';
// 2. Constants for Ratios
var FRONT_END_RATIO = 0.28;
var BACK_END_RATIO = 0.36;
var monthlyGrossIncome = annualIncome / 12;
var monthlyTaxRate = (taxRate / 100) / 12; // Monthly tax rate based on home value
var monthlyInsurance = annualInsurance / 12;
var r = (interestRate / 100) / 12; // Monthly interest rate
var n = loanTermYears * 12; // Total payments
// 3. Calculate Max Allowable Monthly Payment (PITI + HOA) based on ratios
// Scenario A: Front End Limit (Housing costs only)
var maxPaymentFront = monthlyGrossIncome * FRONT_END_RATIO;
// Scenario B: Back End Limit (Housing + Debts)
var maxPaymentBack = (monthlyGrossIncome * BACK_END_RATIO) – monthlyDebt;
// The safe limit is the lower of the two
var maxTotalMonthlyHousingCost = Math.min(maxPaymentFront, maxPaymentBack);
// If debts are too high, maxPaymentBack could be negative
if (maxTotalMonthlyHousingCost <= 0) {
document.getElementById('maxHomePrice').innerText = "$0";
document.getElementById('maxMonthlyPayment').innerText = "$0";
return; // Exit early
}
// 4. Reverse Engineer the Home Price
// Formula: MaxPayment = (Loan * M_Factor) + (Price * Tax_Factor) + Insurance + HOA
// Loan = Price – DownPayment
// MaxPayment = ((Price – Down) * M_Factor) + (Price * Tax_Factor) + Insurance + HOA
// MaxPayment – Insurance – HOA + (Down * M_Factor) = Price * (M_Factor + Tax_Factor)
// Price = (MaxPayment – Insurance – HOA + (Down * M_Factor)) / (M_Factor + Tax_Factor)
// Mortgage Factor (Principal + Interest per dollar borrowed)
// If interest is 0 (edge case), M_Factor is 1/n
var mortgageFactor = 0;
if (r === 0) {
mortgageFactor = 1 / n;
} else {
mortgageFactor = (r * Math.pow(1 + r, n)) / (Math.pow(1 + r, n) – 1);
}
var numerator = maxTotalMonthlyHousingCost – monthlyInsurance – monthlyHOA + (downPayment * mortgageFactor);
var denominator = mortgageFactor + monthlyTaxRate;
var maxHomePrice = numerator / denominator;
// Edge case: if calculated price is less than down payment (math oddity with low income), cap it?
// Or if maxHomePrice < 0
if (maxHomePrice < 0) maxHomePrice = 0;
// 5. Calculate Breakdown derived from Price
var loanAmount = maxHomePrice – downPayment;
if (loanAmount < 0) loanAmount = 0;
var estMonthlyTax = maxHomePrice * monthlyTaxRate;
var principalAndInterest = loanAmount * mortgageFactor;
// Verify total matches limit
var totalMonthlyCheck = principalAndInterest + estMonthlyTax + monthlyInsurance + monthlyHOA;
// 6. Display Results
// Formatting function
function formatMoney(num) {
return '$' + num.toLocaleString('en-US', {maximumFractionDigits: 0});
}
document.getElementById('maxHomePrice').innerText = formatMoney(maxHomePrice);
document.getElementById('maxMonthlyPayment').innerText = formatMoney(totalMonthlyCheck);
document.getElementById('loanAmount').innerText = formatMoney(loanAmount);
document.getElementById('estTax').innerText = formatMoney(estMonthlyTax);
document.getElementById('estIns').innerText = formatMoney(monthlyInsurance);
// Calculate Closing Costs (Estimate 3%)
var closingCosts = maxHomePrice * 0.03;
document.getElementById('closingCosts').innerText = formatMoney(closingCosts);
// Determine which ratio was the limiting factor
var dtiText = "";
if (maxPaymentBack < maxPaymentFront) {
dtiText = "36% (Back-End)";
} else {
dtiText = "28% (Front-End)";
}
document.getElementById('dtiUsed').innerText = dtiText;
}