FTB will pay interest on corporate tax refunds
The FTB will pay 1% interest on corporate tax overpayments beginning July 1, 2017. (FTB Tax News (June 2017)) The interest rate for refunds had been 0% since July 1, 2009.
The FTB will continue collecting 4% interest on corporate underpayments, and the interest rate for overpayments and underpayments of personal income tax remains at 4%.
You can see historical interest rates going back to 1985 at: www.caltax.com/store/image/files/ORP-PDF/secondhalf20171.pdf