date_modify relative time I'd like to reopen this question: 

The answer was a plugin called Nice Time

But This plugin is depricated and the creator stats that this functionality is acheivable via the date_modify filter.

Yes okay, but how?

I have a event archive where I want to show "This event happend xy days ago".

There is a time_diff filter in twig. But it seems as if this is not activated in craft.
You could use the diff method to get the number of days between two dates. So for example:

{{ date(entry.dateCreated|date('c')).diff(now).days }} days ago


In my example between today (using now) and the entry.dateCreated.

There is a explanation as to why you need to wrap the first date in the date filter here, which is where I got the answer from!