My formula spreadsheet dutifully factors in starter hydration to determine final dough hydration. For example, if 100g of 100% hydration starter is added to my dough, my spreadsheet counts that as 50g flour and 50g water toward overall dough hydration.
But metabolic activities of starter culture by definition break down sugars in flour into CO2 and H2O. Thus, a jar of starter after 12 hours of metabolic activity will have a higher hydration than it started with.
Has anyone grappled with this question and come up with a more accurate method for determining starter contribution to dough flour and water? By visual comparison, I would estimate a 100% hydrated starter near its end has about the consistency of a 125% hydrated starter near its beginning.