How can I adjust the date of a post so that it shows how many days have passed since it was published?

The following adjustment must be made in functions.php:

add_filter('get_the_date', 'convert_to_time_ago', 10, 1);
add_filter('the_date', 'convert_to_time_ago', 10, 1);
add_filter('get_the_time', 'convert_to_time_ago', 10, 1);
add_filter('the_time', 'convert_to_time_ago', 10, 1);
    function convert_to_time_ago($orig_time) {
		if ( ! is_admin() ) {
            global $post;
            $orig_time = strtotime($post->post_date);
            return human_time_diff($orig_time, current_time('timestamp')) . ' ' . __('ago');
        } else {
            return $orig_time;
    }
}