(1) All support orders shall be stated in monthly amounts payable on the first of each month in advance. A support obligation not paid by the last day of the month in which it accrues is past due. If a support order does not state the amount of support as a monthly amount, the support amount stated in the order shall be converted to a monthly amount using the formula established by the state court administrative office.

  (2) If payments under a support order are being made in the amount required, through income withholding, pursuant to an installment payment order, or otherwise, and there are no preexisting arrearages, the friend of the court shall not consider the payer as having an arrearage if a periodic temporary arrearage is created by the conversion of the monthly support order to an income withholding order or other payment schedule or results from a divergence between the cycle of payments under the income withholding or payment schedule and the cycle of charges.

  (3) If a support order takes effect on other than the first day of a month, the monthly amount is prorated based on the daily amount for that month. A monthly support order amount shall not be prorated for the last month in which the order is in effect.

  (4) If the title IV-D agency receives a support payment that, at the time of its receipt, exceeds a payer’s support amount payable plus an amount payable under an arrearage payment schedule, the title IV-D agency shall apply the excess against the payer’s total arrearage accrued under all support orders under which the payer is obligated. If a balance remains after application against the total arrearage, the title IV-D agency shall do 1 of the following:

  (a) If the payer designates the balance as additional support, immediately disburse that amount to the recipient of support.

  (b) If, at the time the payment is received, the payer is obligated under a support order for a future support payment and the balance is less than or equal to the monthly support order amount, retain the balance and disburse it to the recipient of support immediately when the amount is payable as support.

  (c) If, at the time the payment is received, the payer is not obligated for a future support payment, or the payer is obligated under a support order for a future support payment but the balance is greater than the monthly support order amount, return the balance to the payer.

  (5) After 1 year after the date the amendatory act that added this subsection is enacted into law, if a payer has paid money that has not been disbursed to the payee and the payer is entitled to a refund of all or a portion of the money because support has been abated in whole or in part, the refund shall be applied first to any support past due in the case and then to any past due support the payer owes in another case. Any balance after the application of the money to support arrearages shall be refunded to the payer.