The reserve ratio formula is given as T=A*(1-r)^n. T is the amount of money the bank can loan out, r is the reserve ratio, A is the amount of money flowing in to the bank, and n is the period of time being evaluated. As an example, imagine a bank with an income of $10 billion and a reserve ratio of 10 percent in the second quarter of the business year. The reserve ratio formula for this bank would be T=10 billion*90².