PHP echo日期：函数名必须是字符串错误

I'm writing registration form but when I need to print date to page just for them to be sure that they gave the right date it says:

Fatal error: Function name must be a string in [address]

Do you have any idea what's the problem? Here is the important part of the form:

<form action='/register.php' method='post'>
<input type='date' id='regdate' name='regdate'>
</form>

And here is the php to print it (in registration.php)

<?php
$bdate = $_POST("regdate");
$ebd = date("m-d-Y",$bdate);
echo $ebd;
?>

Try this code

<?php
$bdate = $_POST["regdate"];
$ebd = date("m-d-Y",strtotime($bdate));
echo $ebd;
?>