Repeating patterns like weekly or monthly are quite common. With Teamup, it's also possible to set a repeating pattern for every X number of months. For example, every 3 months (quarterly) or every 6 months (biannually).
Here's how to do this on the Teamup app:
Open or create the event.
Tap the Does not repeat option to open the repeating menu.
Tap Repeats monthly.
Set the Every option to the number of months desired between recurrences, e.g. 6 months: