The old pay system is made up of different remuneration components, such as basic salary, bonus and fringe benefits (travelling allowances, employer-owned vehicles etc), which will usually be different for employees within the same company.
With cost to company, on the other hand, all the different components (basic, bonus and fringe benefits) are added into one rand amount.
If you look at the definition for gross income for taxation purposes, you will find that all the basic, bonus and fringe benefits are included in the definition for gross income.
One of the main reasons to convert to the new system is because of the changes made to the Income Tax Act in the past years.
Read more about ~ucost to company and medical aid#www.businesslive.co.za/businessexchange/2011/10/08/q-a-choosing-a-way-of-paying-your-staff~