Is there a formula for building a levain?

I want a 115g levain.

I'm maintaining a 60 gram 100% hydration dark rye starter at 20g:20g;20g starter:flour:water on a once-a-day feeding schedule.

I'm going to make a bread flour loaf on bake day and want the most active, healthy, and powerful levain I can use for an 800g total weight bread.

Is there a calculation or formula I should know about or do I just play around with numbers until I build something "close enough?"

Murph