How to calculate interest on gst

Our GST Liabilities is Rs. 100000/-  -----

ITC Available Rs. 50000/- ----------

Balance to pay through E-Payment Rs. 50000/- --------

As per GST rules we have to pay total liabilities of Rs.100000/- at One Time ... There is no option to pay part by part

Question: If we make E-payment of Rs. 50000/- on 25th Day ... then how to calculate Interest on late payment ???

Which amount to be calculated  --- 1) Total Liablities Rs. 100000/- or 2) Balance E-payment Rs. 50000/-

Please reply and calculate

thanks,,,,, best regards