dear Sonali,
Retro active accounting is basically the standard procedure of SAP-HCM which caters the changes in the last period.
For example: You have run the payroll for the month of SEpt 2014. After posting this payroll management want to pay the incentive amount to the employees from Sept , Here what u have to do is simple maintain the amount of incentive in wage type and it will automatically take impact in October s payroll.
Hope your question is answered
Regards,
Jainab