Calculate Interest Rate on Loan Formula
.mc-calculator-widget {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
max-width: 800px;
margin: 20px auto;
border: 1px solid #e0e0e0;
border-radius: 8px;
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box-shadow: 0 4px 6px rgba(0,0,0,0.05);
overflow: hidden;
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padding: 30px;
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gap: 30px;
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flex: 1;
min-width: 300px;
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flex: 1;
min-width: 280px;
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flex-direction: column;
justify-content: center;
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margin-bottom: 15px;
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.mc-input-group label {
display: block;
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font-weight: 600;
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.mc-input-group input {
width: 100%;
padding: 10px;
border: 1px solid #ccc;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box;
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.mc-input-group input:focus {
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outline: none;
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.mc-btn {
width: 100%;
padding: 12px;
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border-radius: 4px;
font-size: 18px;
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cursor: pointer;
transition: background-color 0.2s;
margin-top: 10px;
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.mc-btn:hover {
background-color: #219150;
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.mc-result-row {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px solid #e9ecef;
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.mc-result-row:last-child {
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margin-top: 15px;
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.mc-result-label {
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.mc-result-value {
font-weight: bold;
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.mc-content {
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.mc-content h3 {
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margin-top: 25px;
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.mc-content ul {
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.mc-content li {
margin-bottom: 8px;
}
function calculateMortgage() {
var homePrice = parseFloat(document.getElementById("mcHomePrice").value);
var downPayment = parseFloat(document.getElementById("mcDownPayment").value);
var annualRate = parseFloat(document.getElementById("mcInterestRate").value);
var years = parseFloat(document.getElementById("mcLoanTerm").value);
var annualTax = parseFloat(document.getElementById("mcPropertyTax").value);
var annualInsurance = parseFloat(document.getElementById("mcInsurance").value);
if (isNaN(homePrice) || isNaN(downPayment) || isNaN(annualRate) || isNaN(years)) {
alert("Please enter valid numbers for the primary loan details.");
return;
}
// Handle defaults for tax/insurance if empty
if (isNaN(annualTax)) annualTax = 0;
if (isNaN(annualInsurance)) annualInsurance = 0;
var principal = homePrice – downPayment;
var monthlyRate = (annualRate / 100) / 12;
var numberOfPayments = years * 12;
var monthlyPI = 0;
// Formula: M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
if (annualRate === 0) {
monthlyPI = principal / numberOfPayments;
} else {
var numerator = monthlyRate * Math.pow(1 + monthlyRate, numberOfPayments);
var denominator = Math.pow(1 + monthlyRate, numberOfPayments) – 1;
monthlyPI = principal * (numerator / denominator);
}
var monthlyTax = annualTax / 12;
var monthlyInsurance = annualInsurance / 12;
var totalMonthly = monthlyPI + monthlyTax + monthlyInsurance;
// Formatting currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
document.getElementById("resPrincipalInterest").innerHTML = formatter.format(monthlyPI);
document.getElementById("resTax").innerHTML = formatter.format(monthlyTax);
document.getElementById("resInsurance").innerHTML = formatter.format(monthlyInsurance);
document.getElementById("resTotal").innerHTML = formatter.format(totalMonthly);
}
// Run calculation once on load to show initial state
window.onload = function() {
calculateMortgage();
};