Calculate percentage function

October 2, 2022

Struggling to get the desired results, code to test
The first two functions work, but the third one for the discount does not.
Depending on the number I put in the input field it should apply a discount up to 20% max on increments of 5,(so 1 = 5%, 2 = 10%, etc). No matter the value I put in the input field (deadline) value is stuck in applying the 20% discount. Full bit for testing:

//Dropdown list calculation//
var service_prices = new Array();
service_prices["0"] = 0;
service_prices["1500"] = 1500;
service_prices["4000"] = 4000;
service_prices["8000"] = 8000;

function getServicePrice() {
  var serviceOptionPrice = 0;
  var form = document.forms["formulario"];
  var selectedOption = form.querySelector("#servicePrice");
  if (service_prices[selectedOption.value]) {
    serviceOptionPrice = service_prices[selectedOption.value];
  }
  return serviceOptionPrice;
}

//checkbox calculation//

function extraPrices() {
  var extraPrices = 0;
  var form = document.forms["formulario"];
  var selectedBoxes = form.querySelectorAll("#selectedBox");
  selectedBoxes.forEach((box) => {
    if (box.checked == true) {
      extraPrices += 400;
    }
  });

  return extraPrices;
}
//discount calc
const getDiscountPercent = (months) => (months < 4 ? months * 0.05 : 0.2);

const getTotal = (servicePrice, extraPrice, months) => {
  const disTotal = servicePrice + extraPrice;
  const discountPercent = getDiscountPercent(months);

  return disTotal - disTotal * discountPercent;
};

//total final calc//

function Total() {
  var finalPrice = (getServicePrice() + extraPrices()) * getDiscountPercent();
  document.getElementById("result").value = "€" + finalPrice;
}

<form action="" id="formulario" name="formulario">
  <p> Type of Service
  </p>
  <select name="serviço" id="servicePrice" onchange="Total()">
    <option value="none">Select a service
    </option>
    <option value="1500">1500€
    </option>
    <option value="4000">4000€
    </option>
    <option value="8000">8000€
    </option>
  </select>
  <br>
  <p>Deadline (months)
  </p> 
  <input type="number" class="InStyle" id="months" name="months" onkeydown="Total()">
  <br>
  <!--checkbox-->
  <h1>DESIRED EXTRAS
  </h1>
  <br>
  <input type="checkbox" name="selectedBox" value="4" id="selectedBox" onclick="Total()"> Who we are
  <input type="checkbox" name="selectedBox" value="5" id="selectedBox" onclick="Total()"> Where we are
  <br>
  <input type="checkbox" name="selectedBox" value="6" id="selectedBox" onclick="Total()"> Gun Gallery
  <input type="checkbox" name="selectedBox" value="7" id="selectedBox" onclick="Total()"> eCommerce
  <br>
  <input type="checkbox" name="selectedBox" value="8" id="selectedBox" onclick="Total()"> Internal Mangement
  <input type="checkbox" name="selectedBox" value="9" id="selectedBox" onclick="Total()"> News
  <br>
  <input type="checkbox" name="selectedBox" value="9" id="selectedBox" onclick="Total()"> Social Network
  <br> 
  <br> 
  <br>
  <!--result-->
  <h1>Estimated Total
  </h1>
  <input type="text" class="InStyle" disabled id="result">
</form>

>Solution :

You are not passing the months amount to getDiscountPercent function, neither taking months value from the input and also I advice you to use onChange event on month input .

function Total() {
  var months = parseInt(document.querySelector('#months').value);
  var finalPrice = (getServicePrice() + extraPrices()) * getDiscountPercent(months);
  document.getElementById("result").value = "€" + finalPrice;
}