JSFiddle - React, Tailwind, and code Playground

HTML

<select name="data[Finance][startdate][day]" id="FinanceStartdateDay" disabled>
    <option value="01" selected="selected">1</option>
    <option value="02">2</option>
    <option value="03">3</option>
    <option value="04">4</option>
    <option value="05">5</option>
    <option value="06">6</option>
    <option value="07">7</option>
    <option value="08">8</option>
    <option value="09">9</option>
    <option value="10">10</option>
    <option value="11">11</option>
    <option value="12">12</option>
    <option value="13">13</option>
    <option value="14">14</option>
    <option value="15">15</option>
    <option value="16">16</option>
    <option value="17">17</option>
    <option value="18">18</option>
    <option value="19">19</option>
    <option value="20">20</option>
    <option value="21">21</option>
    <option value="22">22</option>
    <option value="23">23</option>
    <option value="24">24</option>
    <option value="25">25</option>
    <option value="26">26</option>
    <option value="27">27</option>
    <option value="28">28</option>
    <option value="29">29</option>
    <option value="30">30</option>
    <option value="31">31</option>
</select>
<select name="data[Finance][startdate][month]" id="FinanceStartdateMonth">
    <option value="01">January</option>
    <option value="02">February</option>
    <option value="03">March</option>
    <option value="04">April</option>
    <option value="05">May</option>
    <option value="06" selected="selected">June</option>
    <option value="07">July</option>
    <option value="08">August</option>
    <option value="09">September</option>
    <option value="10">October</option>
    <option value="11">November</option>
    <option value="12">December</option>
</select>
<select name="data[Finance][startdate][year]" id="FinanceStartdateYear">
    <option value="2015">2015</option>
    <option value="2014" selected="selected">2014</option>
    <option value="2013">2013</option>
</select>
<br>
<input...

JavaScript

$(document).ready(function () {
    $('#FinanceStartdateMonth').on('change', setCardExpiry);
    $('#FinanceStartdateYear').on('change', setCardExpiry);

});


function setCardExpiry() {

    var startDate = new Date($('#FinanceStartdateYear').val(), $('#FinanceStartdateMonth').val() - 1, 1);
    console.log(startDate);
    var newEnddate = new Date(startDate.getFullYear(), startDate.getMonth() + 12, startDate.getDate());
    newEnddate.setDate(newEnddate.getDate() - 1);
    console.log(newEnddate);

    $('#enddate').val(newEnddate.getFullYear() + "-" + ('00' + (newEnddate.getMonth() + 1)).substr(-2, 2) + "-" + newEnddate.getDate());

}