wordpress CF7 get current quarter in year with jQuery function

Question

this script calculate the correct quarter of the year, but i should calculate the value based on the selected first date :-( can you help me, please?

/* Javascript */
jQuery(function ($) {
   var now = new Date();
   var day = ("0" + now.getDate()).slice(-2);
   var month = ("0" + (now.getMonth() + 1)).slice(-2);
   var today = now.getFullYear()+"-"+(month)+"-"+(day);
   $('#MydatePicker').val(today);   
/*  $("#MydatePicker").attr("min", today); */
});

jQuery(function ($) {
    var now = new Date();
    var day = ("0" + now.getDate()).slice(-2);
    var month = ("0" + (now.getMonth() + 1)).slice(-2);
    var today = now.getFullYear()+"-"+(month)+"-"+(day);
    var quarter;
    if (month < 4)
    quarter = 1;
    else if (month < 7)
     quarter = 2;
    else if (month < 10)
    quarter = 3;
    else if (month < 13)
    quarter = 4;
    $('#trimestre').val(quarter);
});