Michigan interest rate increased for second half of 2017 — MICHIGAN — Interest Rates The annual rate of interest due on Michigan tax deficiencies and overpayments for the period from July 1, 2017, through December 31, 2017, is increased from 4.5% to 4.7%. The effective annual rate of 4.7% was established at one percentage point above the adjusted prime rate charged by three commercial banks to large businesses. (Revenue Administrative Bulletin 2017-9, Michigan Department of T