58. Where the return filed by an employer shows the amount of salary and wages on which an employee has made contributions for a year under this Act or a similar plan, the amount determined under the second paragraph for the year may, in prescribed circumstances, be substituted, in computing the amount determined under sections 56 to 56.5, for the amount shown in the return as the aggregate of the deductions at source for the year under this Act or the similar plan with respect to such employee.
The amount to which the first paragraph refers is equal to the aggregate of
(a) for an amount computed under section 56 or 56.1,i. an amount equal to the product of one-half of the base contribution rate for the year and the amount shown in the return as the salary and wages, less than or equal to the employee’s maximum pensionable earnings, on which the employee has made a base contribution for the year under this Act, and
ii. an amount equal to the product of the base contribution rate for employees for the year under the similar plan and the amount shown in the return as the salary and wages, less than or equal to the employee’s maximum pensionable earnings, on which the employee has made a base contribution for the year under the plan;
(b) for an amount computed under section 56.2 or 56.3,i. an amount equal to the product of one-half of the first additional contribution rate for the year and the amount shown in the return as the salary and wages, less than or equal to the employee’s maximum pensionable earnings, on which the employee has made a first additional contribution for the year under this Act, and
ii. an amount equal to the product of the first additional contribution rate for employees for the year under the similar plan and the amount shown in the return as the salary and wages, less than or equal to the employee’s maximum pensionable earnings, on which the employee has made a first additional contribution for the year under the plan; and
(c) for an amount computed under section 56.4 or 56.5,i. an amount equal to the product of one-half of the second additional contribution rate for the year and the amount shown in the return as the salary and wages, greater than the employee’s maximum pensionable earnings, on which the employee has made a second additional contribution for the year under this Act, and
ii. an amount equal to the product of the second additional contribution rate for employees for the year under a similar plan and the amount shown in the return as the salary and wages, greater than the employee’s maximum pensionable earnings, on which the employee has made a second additional contribution for the year under the plan.