Loan Interest Calculator
:root {
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line-height: 1.6;
background-color: var(–light-background);
color: var(–text-dark);
padding: 20px;
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.loan-calc-container {
max-width: 700px;
margin: 30px auto;
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border-radius: 8px;
box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
overflow: hidden;
display: grid;
grid-template-columns: 1fr;
gap: 30px;
padding: 30px;
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.calculator-header {
text-align: center;
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color: var(–white);
padding: 25px 0;
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margin: -30px -30px 0 -30px;
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.calculator-header h2 {
margin: 0;
font-size: 2em;
font-weight: 700;
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.input-section, .result-section {
padding: 20px;
border: 1px solid var(–gray-border);
border-radius: 6px;
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.input-group {
margin-bottom: 20px;
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.input-group input[type="number"],
.input-group input[type="text"] {
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.input-group input[type="text"]:focus {
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.input-group .currency-symbol {
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color: var(–text-light);
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.input-group.currency .currency-symbol {
left: 12px;
top: 37px;
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.input-group.currency input[type="number"] {
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.input-group.percent .percent-symbol {
right: 12px;
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.input-group.percent input[type="number"] {
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/* Responsive adjustments */
@media (max-width: 600px) {
.loan-calc-container {
padding: 20px;
margin: 20px auto;
}
.calculator-header h2 {
font-size: 1.7em;
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}
$0.00
Total Interest Paid
Understanding Loan Interest Calculation
Calculating the total interest paid on a loan is crucial for understanding the true cost of borrowing. This calculator helps you determine this amount based on the loan principal, interest rate, and repayment term. Loans typically involve paying back both the principal amount borrowed and the interest accrued over time. The interest is essentially the fee charged by the lender for the use of their money.
How the Calculation Works
The most common method for calculating loan payments and interest is using the annuity formula. While this calculator focuses on the total interest, it's derived from the monthly payment calculation. The formula for the monthly payment (M) is:
M = P [ i(1 + i)^n ] / [ (1 + i)^n – 1]
Where:
P = Principal loan amounti = Monthly interest rate (Annual Rate / 12)n = Total number of payments (Loan Term in Months)
Once the monthly payment (M) is calculated, the total amount paid over the life of the loan is simply M * n. The total interest paid is then the total amount paid minus the original principal:
Total Interest = (M * n) - P
Example Calculation
Let's illustrate with a realistic example:
- Loan Amount (P): $20,000
- Annual Interest Rate: 6%
- Loan Term: 5 years (which is 5 * 12 = 60 months)
First, we convert the annual rate to a monthly rate:
i = 6% / 12 = 0.06 / 12 = 0.005
Next, we calculate the monthly payment (M):
M = 20000 [ 0.005(1 + 0.005)^60 ] / [ (1 + 0.005)^60 – 1]
M = 20000 [ 0.005(1.005)^60 ] / [ (1.005)^60 – 1]
M = 20000 [ 0.005(1.34885) ] / [ 1.34885 – 1]
M = 20000 [ 0.00674425 ] / [ 0.34885 ]
M = 20000 * 0.0193328
M ≈ $386.66
Now, we find the total amount paid:
Total Paid = $386.66 * 60 months = $23,199.60
Finally, we calculate the total interest:
Total Interest = $23,199.60 - $20,000 = $3,199.60
So, for a $20,000 loan at 6% for 5 years, you would pay approximately $3,199.60 in interest.
When is this Calculator Useful?
- Mortgages: Estimating the interest on a home loan.
- Auto Loans: Understanding the cost of financing a vehicle.
- Personal Loans: Planning for the repayment of unsecured loans.
- Business Loans: Assessing the financial impact of borrowing for a business.
- Debt Comparison: Comparing the total interest costs of different loan offers.
By using this calculator, you gain a clearer financial picture and can make more informed borrowing decisions.
function calculateTotalInterest() {
var loanAmount = parseFloat(document.getElementById("loanAmount").value);
var annualInterestRate = parseFloat(document.getElementById("annualInterestRate").value);
var loanTermMonths = parseInt(document.getElementById("loanTermMonths").value);
var resultSection = document.getElementById("result-section");
var totalInterestDisplay = document.getElementById("totalInterestDisplay");
if (isNaN(loanAmount) || isNaN(annualInterestRate) || isNaN(loanTermMonths) ||
loanAmount <= 0 || annualInterestRate < 0 || loanTermMonths 0) {
monthlyPayment = P * (monthlyInterestRate * Math.pow(1 + monthlyInterestRate, n)) / (Math.pow(1 + monthlyInterestRate, n) – 1);
} else {
monthlyPayment = P / n; // Simple division if interest rate is 0
}
var totalAmountPaid = monthlyPayment * n;
var totalInterest = totalAmountPaid – P;
// Format to currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
minimumFractionDigits: 2,
maximumFractionDigits: 2
});
totalInterestDisplay.textContent = formatter.format(totalInterest);
resultSection.style.display = "block";
}