Need to display a date that recurs every 6 months

Hi, so I'm looking to calculate the next repeating 6 month event in order to display the next event plus an automation to notify people.

So every June and December we schedule a preventative maintenance event. How can I calculate the next event in the future in order to display that as a widget on a dashboard as well as trigger an automation?

This doesn't sound too difficult, I just can't quite get there. Thanks.