For most American households, April showers bring May flowers and, even better, tax refunds. In 2018 roughly 73% of individual income tax filers received money back, averaging a refund of $2,899. In many ways, that’s a good thing. But it also means that millions of households are together missing out on billions of dollars.

Despite worries earlier this year about shrinking refund checks, the latest IRS statistics suggest that the share of taxpayers receiving refunds and the size of their checks are roughly in line with where those figures stood at the same time last year. This is encouraging news: our tax system functions much more smoothly when the majority of taxpayers are due a refund at filing time.

The catch is that the IRS does not pay interest to people who overpay–that is, who have more money withheld from their paychecks or who make larger estimated tax payments than what they actually owe. This means that overpaying your taxes is equivalent to depositing your money in a savings account with an interest rate of zero.

Read more at Time