Source

File: wp-includes/functions.php

function wp_timezone_override_offset() {
	$timezone_string = get_option( 'timezone_string' );
	if ( ! $timezone_string ) {
		return false;
	}

	$timezone_object = timezone_open( $timezone_string );
	$datetime_object = date_create();
	if ( false === $timezone_object || false === $datetime_object ) {
		return false;
	}
	return round( timezone_offset_get( $timezone_object, $datetime_object ) / HOUR_IN_SECONDS, 2 );
}