User839733648 posted
Hi JagjitSingh,
It seems that you've used something related to bootstrap datepicker, right?
In my opinion, you could use .daterangepicker() function to set the start date and end date.
When you choose any month's 1st day, then the txt_Date will show the end day of that month.
For more, you could refer to the code below.
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.css" rel="stylesheet" />
<script type="text/javascript" src="https://cdn.jsdelivr.net/bootstrap.daterangepicker/2/daterangepicker.js"></script>
<link rel="stylesheet" type="text/css" href="https://cdn.jsdelivr.net/bootstrap.daterangepicker/2/daterangepicker.css" />
<script type="text/javascript">
$(function () {
$('#txt_Date1').daterangepicker({
singleDatePicker: true,
locale: { format: "DD-MM-YYYY" }
}, function (start, end, label) {
if (start) {
var end = start.clone().endOf('month');
$('#txt_Date2').data('daterangepicker').setStartDate(end.startOf('day'));
$('#txt_Date2').data('daterangepicker').setEndDate(end.endOf('day'));
}
});
$('#txt_Date2').daterangepicker({
singleDatePicker: true,
locale: { format: "DD-MM-YYYY" }
});
})
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:TextBox ID="txt_Date1" runat="server" CssClass="form-control datepicker"></asp:TextBox>
<asp:TextBox ID="txt_Date2" runat="server" CssClass="form-control datepicker"></asp:TextBox>
</div>
</form>
</body>
</html>
result:

Best Regards,
Jenifer