Interest on gst

As per the proviso to section 50 of cgst act w.e.f , interest on GST can be calculated on Net Liability , ie, for the amount paid through cash ledger.

So my question is , if for a particular month, I have paid cgst rs.300000/- and the same month paid sgst rs.50000/- in that, I believe that 18% interest should be calculated on cgst amount and sgst amount separately.is it correct,?

Because, some persons are calculating interest on total amount of RS.350000/- and divide it's interest by 2. I think it's wrong. Isn't it?