Recent scholarly research has studied past recessions to develop rainy day fund rules of thumb based on the average revenue shortfalls during an economic downturn. Wagner & Elder, for example, found that “the typical state can expect a revenue shortfall equal to 13 to 18 percent of revenue during a normal downturn." To achieve this during a typical period of economic expansion, states would need to save between 2.4 percent and 2.8 percent of each year’s revenues during good economic times.
In 2006, the peak year for state rainy day funds between 2001 and 2012, only Alaska and Wyoming had accumulated at least 13 percent of their annual general fund spending level in reserve funds (see Table 2). Aside from those two states, North Dakota, and Oklahoma, all states had accumulated less than 10 percent of their annual general fund spending amount in a reserve fund.
Admittedly, developing a rule of thumb is difficult, as state revenue systems vary in reliance on different types of taxes. States with highly progressive income-based tax systems tend to experience more volatility and should therefore have larger reserves to weather economic downturns. States that rely more on consumption taxes, which tend to be more stable, need not have as much in reserves to smooth over revenue declines.
Having a well-funded rainy day fund may not obviate the need for making difficult programmatic cuts during an economic downturn but it can cushion the fiscal system in the short-term. Well-designed rainy day funds should have set rules for filling and withdrawing the funds, a targeted amount to save that takes into account the state’s historical revenue volatility, and good transparency to ensure that citizens are informed about how the fund operates and is used.
They’re right.