(1)    General limitation. The maximum retirement benefits payable to a participant in a calendar year, excluding benefits attributable to contributions subject to the limit under s. 40.32, may not exceed the maximum benefit limitation established under section 415 (b) of the Internal Revenue Code, as adjusted under section 415 (d) of the Internal Revenue Code and any applicable regulations or guidance adopted under the Internal Revenue Code, except that the limit for an individual who first became a participant before January 1, 1990, may not be less than the accrued benefits of the participant, as determined without regard to any changes to the retirement system after October 14, 1987.

   (3)   Treatment of defined benefit and defined contribution plans. For the purpose of determining whether a participant’s retirement benefits exceed the maximum retirement limitations under this section, all defined benefit plans of the employer, including defined benefit plans that are terminated, shall be treated as a single defined benefit plan and all defined contribution plans of the employer, including defined contribution plans that are terminated, shall be treated as a single defined contribution plan. The department may provide by rule additional limitations for participants who are participating in more than one retirement system.

   (4)   Division of benefits. For the purpose of determining whether a participant’s retirement benefits exceed the maximum retirement limitations under this section for a participant whose retirement benefits have been divided under s. 40.08 (1m), the participant’s retirement benefits shall be measured as if no division had occurred.