Service tax Calculation???

Hi All,

Our organization is doing construction and interial works, in this both service tax and Vat applicable. While we raise the invoice, total amounts 33.33% we calculate service tax @ 10.3% and for 66.66% of total amount we calculate vat @ 12.5%. Since service tax is only we need to pay while time of receipt, what is the calculation is to be done to know the service tax amount when we receive an amount of Rs.50000/-.

Please help me,

Thanks and Regards,

Biju