Formula that can calculate Year to Date % success across multiple years

Hi guys,

I was wondering if you could help me. I have been able to calculate a % success rate of steps within a particular month, but haven't found a way to average the monthly success rates so far (year to date).
Issue is that the averaging needs to restart when a new year begins.
Would any of you know what formula to use for this?

Attached is a sample of what I'm trying to achieve.

Thanks for your help,
Allard