add_filter("gform_confirmation", "custom_confirmation", 10, 4);
function custom_confirmation($confirmation, $form, $lead, $ajax){
$redirurl = $_POST["input_6"];
    if($form["id"] == "1"){
	$confirmation = array();
	$confirmation['redirect'] = $redirurl;
    }
    return $confirmation;
}

add_filter("gform_pre_render_1", "redirecturl");
add_filter("gform_admin_pre_render_1", "redirecturl");
function redirecturl($form){
 foreach($form["fields"] as &$field){
	if($field["id"] == 6){
		$field["defaultValue"] = $_SERVER['HTTP_REFERER'];
	}
 }
 return $form;
}