All added value is increased on the supply of goods and service with an indirect tax method. For calculating GST, the rate slab is to be understood by the taxpayer initially. GST amount = Actual cost of an item / Product with the percentage of GST imposed is divided by 100.
When GST is Rs. 1,000 and the estimated slab is 18% GST then 1,000+ 1,000 X (18/100) 1,000+180 = Rs. 1,180.