calculation of gst

calculation of gst is not not complicated. you just need to find out the taxable value of goods or services through valuation rule and multiply the value with the rates prescribed. however finding taxable value is the real task.
in normal cases the taxable value is what you charge from customer for goods or services excluding tax.
For example you sold goods worth rs 50000 to someone excluding the tax than taxable value will be 50000 and you have to charge gst on that value, 5 %...hence you need to charge rs 2500 from customer for gst...total amount will be rs 52500.
however if you charge rs 50000 cum duty, meaning 50000 also include gst...than you have to pay 50000*5/105 = 2380.95 as gst to government.
if you are a composition dealer than you cannot receive gst from customer and you have to pay gst at the rate prescribed on the total turnover value.