The interest rate for tax over/under payments

"Revenue Ruling 2018-32 provides the interest rates for underpayments and overpayments. The rates for interest determined under Section 6621 of the code for the calendar quarter beginning January 1, 2019, will be 6 percent for overpayments (5 percent in the case of a corporation), 6 percent for underpayments,"

Yikes! At least, you can get > 2% interest on a <= 2 year bank savings CD (certificate of deposit) these days. Remember the good old days when the IRS rate = 3%, for something like >= 2.9 && <= 3.1 years in a row? Lowest extended run, ever.

The IRS rate is the rate paid on three month US Treasury Notes plus 3% rounded. For a long time the fed rate was less than 1/2% so the IRS rate was 3%. The fed rate is now 3% so the IRS rate is 6%.