WordPress show button if event start date is before today's date

register_button

function register_button() {
    $output = '';
    $current_date = date_i18n('Y-m-d');
    $date = DateTime::createFromFormat('jS F, Y', get_field('dmc_conference_date'));
    $moddate = $date->format('Y-m-d');
    if ( $moddate < $current_date ) : 
        $output .= '<a href="/pre-register-for-a-conference/" class="button radius large right">Pre-Register for 2015</a>';
    else : 
        $output .= '<a href="' . esc_url(get_field('dmc_conference_rego_link')) . '" class="button radius large right">Register Now</a>';
    endif; 
    return $output;
}