JSFiddle - React, Tailwind, and code Playground

HTML

<div class="date-field required-field col-sm-6">
  <label for="dietaStart">Dieta od</label>
  <input placeholder="Wybierz" data-date-format="dd.mm.yyyy" id="datepicker" name="dietaStart" class="form-control calendar-icon" type="date" required />
</div>

<div class="date-field required-field col-sm-6">
  <label for="dietaKoniec">Dieta do</label>
  <input placeholder="Wybierz" data-date-format="dd.mm.yyyy" id="datepicker2" name="dietaKoniec" class="form-control calendar-icon" type="date" required />
</div>

<h3>Please enter the project Notice to Proceed (NTP) date: <input     id="NtpDate" type= "date" name="NtpDate"></h3>

<h3>Please enter the Report date: <input type= "date" name="ReportDate" id="abc">    </h3>

<span class="price"></span>

JavaScript

$("#datepicker2").on("change", function () {
              var startDate = $("input[name=dietaStart]").val();
              var startDateD = toDate(startDate, "DD-MM-YYYY");
							var startDateE = new Date(startDateD);
  
              var endDate = $("input[name=dietaKoniec]").val();
              var endDateD = toDate(endDate, "DD-MM-YYYY");
              var endDateE = new Date(endDateD);

              var timeDiff = Math.abs(endDateE.getTime() - startDateE.getTime());
              var diffDays = Math.ceil(timeDiff / (1000 * 3600 * 24));
              var dietPrice = diffDays * 75;
              $('.price').text(dietPrice);
            });