#mortgage-calculator-wrapper .calc-container {
background: #f9f9f9;
border: 1px solid #e0e0e0;
border-radius: 8px;
padding: 25px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
margin-bottom: 40px;
}
#mortgage-calculator-wrapper .input-group {
margin-bottom: 15px;
}
#mortgage-calculator-wrapper label {
display: block;
font-weight: 600;
margin-bottom: 5px;
color: #333;
}
#mortgage-calculator-wrapper input,
#mortgage-calculator-wrapper select {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
}
#mortgage-calculator-wrapper .calc-btn {
background-color: #0073aa;
color: white;
border: none;
padding: 12px 20px;
font-size: 16px;
font-weight: bold;
border-radius: 4px;
cursor: pointer;
width: 100%;
margin-top: 10px;
transition: background-color 0.3s;
}
#mortgage-calculator-wrapper .calc-btn:hover {
background-color: #005177;
}
#mortgage-calculator-wrapper .result-box {
margin-top: 25px;
padding: 20px;
background-color: #fff;
border: 1px solid #ddd;
border-radius: 6px;
display: none;
}
#mortgage-calculator-wrapper .result-row {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
font-size: 15px;
color: #555;
}
#mortgage-calculator-wrapper .result-row.highlight {
font-size: 20px;
font-weight: bold;
color: #2c3e50;
border-top: 2px solid #eee;
padding-top: 10px;
margin-top: 10px;
}
#mortgage-calculator-wrapper .seo-content h2 {
color: #23282d;
font-size: 24px;
margin-top: 30px;
}
#mortgage-calculator-wrapper .seo-content h3 {
color: #23282d;
font-size: 20px;
margin-top: 25px;
}
#mortgage-calculator-wrapper .seo-content p {
line-height: 1.6;
color: #444;
margin-bottom: 15px;
}
#mortgage-calculator-wrapper .error-msg {
color: #d63638;
font-weight: bold;
margin-top: 10px;
display: none;
}
Understanding Your Mortgage Calculation
Before committing to a home purchase, it is crucial to understand exactly how your monthly payments are calculated. This Mortgage Calculator helps prospective homeowners estimate their monthly financial obligations by factoring in the home price, down payment, interest rate, and loan term.
How the Mortgage Formula Works
The calculation of your monthly mortgage payment generally follows the standard amortization formula used by lenders worldwide. The core formula determines the monthly Principal and Interest (P&I) payment required to fully pay off the loan by the end of the term.
The formula used is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
Where:
- M is the total monthly payment.
- P is the principal loan amount (Home Price minus Down Payment).
- i is the monthly interest rate (Annual Rate divided by 12).
- n is the total number of payments (Loan Term in years multiplied by 12).
Example Calculation
Let's assume you want to buy a house worth $350,000. You have saved a down payment of $70,000 (20%), leaving a loan amount of $280,000.
If you secure a 30-year fixed-rate mortgage at an interest rate of 6.5%:
- The principal (P) is $280,000.
- The monthly interest rate (i) is 0.065 / 12 = 0.005416.
- The number of payments (n) is 30 * 12 = 360.
Using the calculator above, this results in a monthly payment of approximately $1,769.79 (excluding taxes and insurance). Over the life of the loan, you would pay a total of $637,123, meaning the total interest cost is $357,123.
Why Down Payment Matters
The size of your down payment significantly impacts your monthly mortgage expenses. A larger down payment reduces the principal amount you need to borrow, which directly lowers both your monthly payment and the total interest paid over the life of the loan. Additionally, putting down less than 20% often triggers Private Mortgage Insurance (PMI), which is an extra cost not included in the standard P&I calculation above.
function calculateMortgage() {
// Get input values using var
var homePriceInput = document.getElementById("mcHomePrice").value;
var downPaymentInput = document.getElementById("mcDownPayment").value;
var interestRateInput = document.getElementById("mcInterestRate").value;
var loanTermInput = document.getElementById("mcLoanTerm").value;
var errorDiv = document.getElementById("mcError");
var resultDiv = document.getElementById("mcResult");
// Convert to numbers
var homePrice = parseFloat(homePriceInput);
var downPayment = parseFloat(downPaymentInput);
var interestRate = parseFloat(interestRateInput);
var loanTermYears = parseInt(loanTermInput);
// Validation logic
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(interestRate) || isNaN(loanTermYears) || homePrice <= 0 || interestRate < 0) {
errorDiv.style.display = "block";
resultDiv.style.display = "none";
return;
}
// Reset error
errorDiv.style.display = "none";
// Calculate Loan Details
var principal = homePrice – downPayment;
// Handle edge case where principal is 0 or negative
if (principal 0) {
if (interestRate === 0) {
monthlyPayment = principal / numberOfPayments;
} else {
// M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1 ]
var x = Math.pow(1 + monthlyRate, numberOfPayments);
monthlyPayment = (principal * x * monthlyRate) / (x – 1);
}
totalCost = monthlyPayment * numberOfPayments;
totalInterest = totalCost – principal;
}
// Formatting currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2
});
// Update UI
document.getElementById("resLoanAmount").innerText = formatter.format(principal);
document.getElementById("resMonthlyPayment").innerText = formatter.format(monthlyPayment);
document.getElementById("resTotalInterest").innerText = formatter.format(totalInterest);
document.getElementById("resTotalCost").innerText = formatter.format(totalCost);
// Show results
resultDiv.style.display = "block";
}