Coming up with upper and lower bounds for a KPI

We’ve been tasked with creating a “safe range” for several of our KPIs that will make it easier for leadership to understand when metrics are performing as relatively expected. These KPIs are usually tracked weekly and monthly.

We have carte blanche in terms of methodology. Not sure where to start. How would you approach this initially? Some sort of moving average and the upper and lower bounds being a standard dev from that average? Something more complex?