Mortgage Calculator
.calculator-widget {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 20px;
border: 1px solid #e0e0e0;
border-radius: 8px;
background-color: #f9f9f9;
}
.calculator-title {
text-align: center;
color: #333;
margin-bottom: 20px;
}
.input-group {
margin-bottom: 15px;
display: flex;
flex-direction: column;
}
.input-group label {
font-weight: 600;
margin-bottom: 5px;
color: #555;
}
.input-group input, .input-group select {
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
}
.calc-btn {
width: 100%;
padding: 12px;
background-color: #2c3e50;
color: white;
border: none;
border-radius: 4px;
font-size: 16px;
font-weight: bold;
cursor: pointer;
transition: background 0.3s;
}
.calc-btn:hover {
background-color: #34495e;
}
.results-area {
margin-top: 25px;
padding: 20px;
background-color: white;
border: 1px solid #ddd;
border-radius: 4px;
display: none;
}
.result-row {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
font-size: 16px;
}
.result-row.highlight {
font-size: 20px;
font-weight: bold;
color: #27ae60;
border-top: 1px solid #eee;
padding-top: 10px;
margin-top: 10px;
}
.seo-content {
margin-top: 40px;
line-height: 1.6;
color: #444;
}
.seo-content h2 {
color: #2c3e50;
margin-top: 30px;
}
.seo-content p {
margin-bottom: 15px;
}
.seo-content ul {
margin-bottom: 15px;
padding-left: 20px;
}
.error-msg {
color: #e74c3c;
text-align: center;
margin-top: 10px;
display: none;
}
Understanding Your Mortgage Calculation
Whether you are a first-time homebuyer or looking to refinance, understanding how your mortgage payment is calculated is crucial for financial planning. This Mortgage Payment Calculator helps you estimate your monthly financial commitment based on four primary factors: home price, down payment, interest rate, and loan term.
How the Formula Works
Mortgage amortization uses a specific mathematical formula to determine the monthly payment required to pay off the principal and interest over a set period. The core variables are:
- Principal (P): This is the Home Price minus your Down Payment. It represents the actual amount borrowed from the lender.
- Interest Rate (r): The annual percentage rate charged by the lender. For monthly calculations, this is divided by 12.
- Number of Payments (n): The total number of months in your loan term (e.g., a 30-year loan equals 360 payments).
By adjusting the down payment, you can see how paying more upfront reduces both your monthly obligation and the total interest paid over the life of the loan.
Impact of Interest Rates and Loan Terms
Even a small difference in the interest rate can equate to tens of thousands of dollars in savings or extra costs over 30 years. Similarly, choosing a 15-year term typically results in a higher monthly payment but significantly lowers the total interest paid compared to a 30-year term. Use this tool to compare scenarios and find the balance that fits your monthly budget.
Additional Costs to Consider
While this calculator provides the Principal and Interest (P&I) portion of your payment, remember that most homeowners also pay property taxes, homeowners insurance, and potentially private mortgage insurance (PMI) and HOA fees. These are often bundled into your monthly escrow payment, making your actual cash outflow higher than the P&I figure shown above.
function calculateMortgage() {
// Get input values
var homePrice = parseFloat(document.getElementById('homePrice').value);
var downPayment = parseFloat(document.getElementById('downPayment').value);
var annualRate = parseFloat(document.getElementById('interestRate').value);
var loanYears = parseFloat(document.getElementById('loanTerm').value);
var errorDiv = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('resultsArea');
// Reset display
errorDiv.style.display = 'none';
resultsDiv.style.display = 'none';
// Validation
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(annualRate) || isNaN(loanYears)) {
errorDiv.innerText = "Please enter valid numeric values for all fields.";
errorDiv.style.display = 'block';
return;
}
if (homePrice <= 0 || annualRate < 0) {
errorDiv.innerText = "Please ensure Home Price is greater than 0 and Rate is not negative.";
errorDiv.style.display = 'block';
return;
}
// Logic
var principal = homePrice – downPayment;
if (principal <= 0) {
errorDiv.innerText = "Down payment cannot be greater than or equal to the home price.";
errorDiv.style.display = 'block';
return;
}
var monthlyRate = (annualRate / 100) / 12;
var totalPayments = loanYears * 12;
var monthlyPayment = 0;
// Calculation handling for 0% interest edge case
if (monthlyRate === 0) {
monthlyPayment = principal / totalPayments;
} else {
// Amortization formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
monthlyPayment = principal * ( (monthlyRate * Math.pow(1 + monthlyRate, totalPayments)) / (Math.pow(1 + monthlyRate, totalPayments) – 1) );
}
var totalCost = monthlyPayment * totalPayments;
var totalInterest = totalCost – principal;
// Formatting currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// Display results
document.getElementById('displayLoanAmount').innerText = formatter.format(principal);
document.getElementById('displayTotalInterest').innerText = formatter.format(totalInterest);
document.getElementById('displayTotalCost').innerText = formatter.format(totalCost);
document.getElementById('displayMonthlyPayment').innerText = formatter.format(monthlyPayment);
resultsDiv.style.display = 'block';
}