JSFiddle - React, Tailwind, and code Playground

HTML

<form action="" method="post" id="theForm">
        <fieldset>
            <p>Use this form to calculate your paycheck.</p>                                                     
            <div><label for="hours">Hours Worked</label><input type="text" name="hours" id="hours" value="0.00"></div>
            <div><label for="rate">Pay Rate</label><input type="text" name="rate" id="rate" value="0.00"></div>
            <div><label for="withholding">Withholding</label><input type="text" name="withholding" id="withholding" value="0.20"></div>
            <div><label for="total">Total</label><input type="text" name="total" id="total" value="0.00"></div>
            <div><label for="withheld">Withheld</label><input type="text" name="withhheld" id="withheld" value="0"></div>
            <div><label for="realTotal">Final Total</label><input type="text" name="realTotal" id="realTotal" value="0"></div>
            <div><input type="submit" value="Calculate" id="submit"/></div>
        </fieldset>
    </form>

JavaScript

function calculate() {
    'use strict';
    var totalPay;
    var withheld;
    var realPay;
    var hours = document.getElementById('hours').value;
    var rate = document.getElementById('rate').value;
    var withholding = document.getElementById('withholding').value;

    totalPay = hours * rate;
    withheld = totalPay * withholding;
    realPay = totalPay - withheld;

    document.getElementById('total').value = totalPay;
    document.getElementById('withheld').value = withheld;
    document.getElementById('realTotal').value = realPay;

    return false;
}

function init() {
    'use strict';
    document.getElementById('theForm').onsubmit = calculate;
}

init();