body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 1000px;
margin: 0 auto;
padding: 20px;
background-color: #f9f9f9;
}
.calc-container {
background: #ffffff;
border-radius: 8px;
box-shadow: 0 4px 6px rgba(0,0,0,0.1);
padding: 30px;
margin-bottom: 40px;
border: 1px solid #e1e1e1;
}
.calc-header {
text-align: center;
margin-bottom: 30px;
}
.calc-header h2 {
color: #2c3e50;
margin-bottom: 10px;
}
.calc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 768px) {
.calc-grid {
grid-template-columns: 1fr;
}
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
margin-bottom: 5px;
font-weight: 600;
color: #555;
}
.input-wrapper {
position: relative;
}
.input-wrapper input {
width: 100%;
padding: 10px 10px 10px 35px;
border: 1px solid #ddd;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
.input-wrapper input:focus {
border-color: #3498db;
outline: none;
}
.symbol {
position: absolute;
left: 12px;
top: 11px;
color: #777;
}
.calc-btn {
grid-column: 1 / -1;
background-color: #27ae60;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
width: 100%;
margin-top: 10px;
transition: background-color 0.2s;
}
.calc-btn:hover {
background-color: #219150;
}
.results-section {
grid-column: 1 / -1;
background-color: #f8f9fa;
border-radius: 6px;
padding: 20px;
margin-top: 20px;
border: 1px solid #e9ecef;
display: none;
}
.result-row {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #e1e1e1;
}
.result-row:last-child {
border-bottom: none;
}
.result-label {
color: #666;
}
.result-value {
font-weight: bold;
color: #2c3e50;
}
.big-result {
font-size: 24px;
color: #27ae60;
}
.error-msg {
color: #e74c3c;
text-align: center;
margin-top: 10px;
display: none;
}
.content-article {
background: white;
padding: 40px;
border-radius: 8px;
box-shadow: 0 2px 4px rgba(0,0,0,0.05);
}
.content-article h2 {
color: #2c3e50;
border-bottom: 2px solid #3498db;
padding-bottom: 10px;
margin-top: 30px;
}
.content-article h3 {
color: #34495e;
margin-top: 25px;
}
.content-article p {
margin-bottom: 15px;
font-size: 17px;
}
.content-article ul {
margin-bottom: 20px;
}
.content-article li {
margin-bottom: 10px;
}
Understanding Your Mortgage Calculation
Buying a home is one of the most significant financial decisions you will make. This Mortgage Payment Calculator helps you estimate your monthly financial commitment by breaking down the costs associated with borrowing money for real estate. Unlike simple loan calculators, this tool considers the critical "PITI" components: Principal, Interest, Taxes, and Insurance.
How the Mortgage Formula Works
The core of the calculation uses the standard amortization formula to determine your principal and interest payments:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
- M = Total monthly payment (Principal + Interest)
- P = Principal loan amount (Home Price minus Down Payment)
- i = Monthly interest rate (Annual Rate divided by 12)
- n = Number of payments (Loan Term in years multiplied by 12)
Key Components of Your Monthly Payment
While the loan itself determines the base payment, homeownership costs extend beyond the bank. This calculator accounts for:
1. Principal and Interest (P&I)
This is the money going directly to the bank. In the early years of a 30-year fixed-rate mortgage, the majority of this payment goes toward interest. As time passes, the balance shifts, and you begin paying down more of the principal balance.
2. Property Taxes
Local governments assess property taxes to fund schools, roads, and public services. Lenders typically collect 1/12th of your annual tax bill each month and hold it in an escrow account to pay the bill on your behalf. These rates vary significantly by location, often ranging from 0.5% to 2.5% of the property's assessed value.
3. Homeowners Insurance
Lenders require you to insure the property against damage (fire, storms, theft). Like taxes, this annual premium is usually divided by 12 and added to your monthly mortgage payment.
4. HOA Fees
If you buy a condo or a home in a planned community, you may owe Homeowners Association (HOA) dues. While these are usually paid directly to the association and not the lender, they affect your monthly housing budget and your debt-to-income ratio for loan qualification.
Impact of Interest Rates and Down Payments
Even small changes in your input variables can drastically change your financial outlook:
- Interest Rates: A 1% increase in interest rate on a $300,000 loan can increase your monthly payment by over $180 and cost you over $65,000 in additional interest over 30 years.
- Down Payment: Putting down 20% typically helps you avoid Private Mortgage Insurance (PMI), which is an extra fee lenders charge borrowers with smaller down payments. (Note: This calculator focuses on PITI and does not automatically calculate PMI).
- Loan Term: A 15-year term will have higher monthly payments than a 30-year term, but you will pay significantly less interest over the life of the loan.
Using These Results
Use the "Total Monthly Payment" figure to measure affordability against your monthly household income. Financial advisors generally recommend that your total housing costs (PITI + Utilities) should not exceed 28% of your gross monthly income.
function calculateMortgage() {
// Get Input Values
var price = parseFloat(document.getElementById('homePrice').value);
var down = parseFloat(document.getElementById('downPayment').value);
var rate = parseFloat(document.getElementById('interestRate').value);
var years = parseFloat(document.getElementById('loanTerm').value);
var tax = parseFloat(document.getElementById('propertyTax').value);
var insurance = parseFloat(document.getElementById('homeInsurance').value);
var hoa = parseFloat(document.getElementById('hoaFees').value);
// Validation
var errorDiv = document.getElementById('errorMessage');
var resultsDiv = document.getElementById('resultsSection');
if (isNaN(price) || isNaN(down) || isNaN(rate) || isNaN(years)) {
errorDiv.style.display = 'block';
resultsDiv.style.display = 'none';
return;
}
// Handle optional fields defaulting to 0 if empty
if (isNaN(tax)) tax = 0;
if (isNaN(insurance)) insurance = 0;
if (isNaN(hoa)) hoa = 0;
errorDiv.style.display = 'none';
// Calculations
var principal = price – down;
// Edge case: if principal is <= 0
if (principal <= 0) {
alert("Down payment cannot be greater than or equal to home price.");
return;
}
var monthlyRate = rate / 100 / 12;
var numberOfPayments = years * 12;
// Mortgage Formula: M = P[r(1+r)^n/((1+r)^n)-1)]
var monthlyPI = 0;
if (rate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
monthlyPI = principal * (monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments)) / (Math.pow(1 + monthlyRate, numberOfPayments) – 1);
}
var monthlyTax = tax / 12;
var monthlyInsurance = insurance / 12;
var monthlyTotal = monthlyPI + monthlyTax + monthlyInsurance + hoa;
var totalCost = (monthlyPI * numberOfPayments) + down;
var totalInterest = (monthlyPI * numberOfPayments) – principal;
// Display Results
resultsDiv.style.display = 'block';
// Format Currency Helper
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
document.getElementById('resultPI').innerHTML = formatter.format(monthlyPI);
document.getElementById('resultEscrow').innerHTML = formatter.format(monthlyTax + monthlyInsurance + hoa);
document.getElementById('resultTotal').innerHTML = formatter.format(monthlyTotal);
document.getElementById('resultLoanAmount').innerHTML = formatter.format(principal);
document.getElementById('resultTotalInterest').innerHTML = formatter.format(totalInterest);
document.getElementById('resultTotalCost').innerHTML = formatter.format(totalCost + (monthlyTax * numberOfPayments) + (monthlyInsurance * numberOfPayments) + (hoa * numberOfPayments));
}