Wis. Stat. § 214.58: Payment of interest.

(1) The board of directors shall determine the rate and amount of interest to be paid on or credited to deposit accounts. The board of directors may establish reasonable classifications of accounts based on the types of accounts, the length of time accounts are continued in effect, the size of initial deposits into accounts, the minimum balances of accounts required for payment of interest, the frequency and extent of the activity on accounts, or on other classifications the division may approve.

(2) The board of directors shall determine by resolution the method of calculating the amount of interest on deposit accounts and the date on which interest is to be paid or credited.