If the aforesaid annuity so fixed is not payable, but a larger amount is payable as a minimum annuity, such refund shall be reduced by 5/12 of the value of the difference in the annuity payable and the amount theretofore fixed, as the value of such difference may be at the date and as of the age of the employee when his annuity is granted; provided that if the employee was credited with city contributions for any period for which he made no contribution, or a contribution of less than 3 1/4% of salary, a further reduction in the refund shall be made by the equivalent of what he would have contributed during such period less his actual contributions, had the rate of employee contributions in force on the effective date been in effect throughout his entire service, prior to such effective date, with interest computed on such amounts at the effective rate.
If the employee was credited with city contributions for any period of service during which he was not required to make a contribution, or made a contribution of less than 3 1/4% of salary, the refund shall be reduced by the equivalent of the contributions he would have made during such period, less any amount he contributed, had the rate of employee contributions in effect on the effective date been in force throughout his entire service, prior to the effective date, with interest on such amounts at the effective rate; provided that if the employee was credited with city contributions for widow's annuity for any service prior to the effective date, any amount so refundable shall be further reduced by the equivalent of what he would have contributed had he made contributions for widow's annuity at the rate of 1% throughout his entire service; prior to such effective date, with interest on such amounts at the effective rate.
40 ILCS 5/8-154