D8 Views Argument Default

I'm trying to determine how I can add a Views default argument similar to "Calendar Current Date" in Drupal 8. Specifically I would like my view to show me events in the coming month, not the current,. In the past I would have provided a PHP snippet something like this return date("Ym", now() + 2592000); . But there is no longer a PHP option in D8, only "Calendar Current Date" and others including "Fixed". Can anyone point me in the right direction? Thanks.