Expire an entry according to a date field Ich have a concert entry which I want to expire after the concert is over.

How do I do that? 

I was able to hide past entries like this:

{% set present = now|date_modify("+1 day") %}
{% for entry in craft.entries.section('concert') %}
     {% if entry.konzertdatum &gt; present %}
       {{ entry.konzertdatum|date('d. M. Y - H:i')}} - Concert Bla
     {% endif %}
{% endfor %}


But ist it also possible to expire this entry altogether os its marked in the CP?

Or would it be better to use the post_date as a concert timestamp and then show somehow only future dates?
You can set the Expiration Date in the control panel. It is at the bottom of the column on the right (on wide screens), or at the bottom of the page (on narrow screens). I don't think there is any way to set the Expiration Date from the konzertdatum, so you would have to either use the Expiration Date as the concert date, or maintain both of them.