How long will a starter keep in the fridge?

If I make a starter that contains approximately 223 billion cells for a beer that requires a starter of that size, and refrigerate it to decant and pitch in a week or so, is there a way to determine how much the yeast will degrade per day or per week? How long will a starter remain “fresh” before it starts to degrade?

The typical assumption for yeast stored under beer in the fridge is 25%/month viability loss. So after a week you’d lose roughly 7% of the yeast.