A central bank is insolvent if its plans imply a Ponzi scheme on reserves so the price level becomes infinity. If the central bank enjoys fiscal support, in the form of a dividend rule that pays out net income every period, including when it is negative, it can never become insolvent independently of the fiscal authority. Otherwise, this note distinguishes between intertemporal insolvency, rule insolvency, and period insolvency. While period and rule solvency depend on analyzing dividend rules and sources of risk to net income, evaluating intertemporal solvency requires overcoming the difficult challenge of measuring the present value of seignorage.