Compound interest is the interest calculated on the initial principal amount as well as the accumulated interest from previous periods. The formula to calculate compound interest is:

where: A = the amount after the specified time period P = the principal amount (the initial amount of money) r = the annual interest rate (as a decimal) n = the number of times the interest is compounded per year t = the time period in years

To calculate compound interest, follow these steps:

- Determine the principal amount (P).
- Determine the annual interest rate (r) and the number of times the interest is compounded per year (n).
- Determine the time period (t) in years.
- Plug in the values into the formula above
`A = P(1 + r/n)^(nt)`

. - Solve the equation to find the amount (A).

For example, let’s say you invest $5,000 at an annual interest rate of 5% compounded monthly for 3 years. Using the formula above:

P = $5,000 r = 5% = 0.05 n = 12 (monthly compounding) t = 3 years

Building a loan calculation form using HTML can be a very useful tool. Here is a step-by-step tutorial on how to build a simple loan calculation form using HTML and NittiJS.

## Step 1: Create the HTML Form

The first step is to create an HTML form that will collect user input for the loan amount, interest rate, and loan term. To create the form, you will need to use a combination of HTML form elements such as input, label, and button. Here is an example HTML code for the loan calculation form:

```
<div >
<form>
<div class="mb-3">
<label for="amount" class="form-label">Amount:</label>
<input class="form-control" type="number" id="amount" name="amount" required>
</div>
<div class="mb-3">
<label for="rate" class="form-label">Rate:</label>
<input class="form-control" type="number" value="12" id="rate" name="rate" required>
</div>
<div class="mb-3">
<label for="term" class="form-label">Term:(years)</label>
<input class="form-control" type="number" value="5" id="term" name="term" required>
</div>
<div>
Monthly Payment: <span r-calc="calculateLoanMonthlyPayment" r-format="currency|usd"> </span>
</div>
</form>
</div>
```

To do the calculation, we use NittiJS a free, opensource small library that does calculations based on the input elements in a form.

The Javascript function that does the calculation is this:

```
function calculateLoanMonthlyPayment({amount, rate, term}) {
let interestRate = rate / 100 / 12;
let loanTerm = term * 12;
let monthlyPayment = (amount * interestRate * Math.pow(1 + interestRate, loanTerm)) / (Math.pow(1 + interestRate, loanTerm) - 1);
return monthlyPayment;
}
```

Note that the function `calculateLoanMonthlyPayment`

receives the amount, rate and term as parameters. All that the function has to do is to calculate the monthly payment using the formula above.

Also notice that we don’t have any “calculate” button. The calculation is run as you type the input values or as you update the values.

NittiJS is very useful in building such calculation forms. Read the documentation here.

Here is a complete demo. Try changing the values and/or the code:

See the Pen Loan calculation form (Using NittiJS) by Prasanth (@prasanthmj) on CodePen.

### See Also

- How To Add A Mortgage Calculator To Your Website For Lead Capture: Free Sample Code And Step-By-Step Guide And Live Demo
- How to create a useful calculator widget in plain HTML quickly: sample code and live demo
- BMR (Basal Metabolic Rate) calculation HTML sample code - simple calculation widget HTML code with live demo
- Implementing an Interactive BMI Calculator Using HTML Code for Your Website
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