(1) After December 31, 1986, on January 1 of each year a retirement allowance attributable to a member who first becomes a member on or before January 1, 1995, shall be increased 4% compounded annually.

    (2) Beginning January 1, 1995, each retirement allowance attributable to a member who first becomes a member after January 1, 1995, shall be increased each January 1. The amount of the annual increase shall be equal to 4% of the retirement allowance payable as of the retirement allowance effective date.

    (3) A retirement allowance that begins after January 1 of the immediately preceding calendar year shall be increased under this section on a pro rata basis by the applicable percentage amount from the time the retirement allowance begins to the date of the increase.