The adjusted interest rates for underpayments and overpayments of California personal income tax and corporate franchise and income tax will decrease for the period July 1, 2025, through December 31, 2025. The rate will drop to 7% (from 8% for the prior period) for personal income tax underpayments and overpayments and corporate tax underpayments. The rate will drop to 4% (from 5% for the prior period) for corporation tax overpayments. Memorandum, California Franchise Tax Board, January 9, 2025