How they got multiplying factor of 0.1405
Let the Total amount worked out after 1% water charges : W
Let the multiplying factor for GST : f
Total after Water charges : w
Add GST amount : f x w ... ..................... (Fig A)
Total after GST : w + fw
Add CP & OH @ 15% : 0.15 (w + fw)
Amount after CP & OH : 1.15 (w+fw)
(Which is inclusive of GST)
GST = 12%
GST applicable amount : 1.15 (w+ fw)/1.12 (Reverse calculation)
GST amount : 0.12 x 1.15 (w +fw)/1.12 which is equal to figure A above
f x w = 0.12 x 1.15 / 1.12 x w(1 + f)
or
f=0.1232 (1+f)
f-0.1232f=0.1232
0.8768f = 0.1232
f= 0.1232/0.8768
f=0.1405
So, the multiplying factor for GST 12% and CP 15% is 0.1405
What we should adopt for 18% GST and 10% CP & OH is as follows :
Let the Total amount worked out after 1% water charges : W
Let the multiplying factor for GST : f
Total after Water charges : w
Add GST amount : f x w ... ..................... (Fig A)
Total after GST : w + fw
Add CP & OH @ 10% : 0.10 (w + fw)
Amount after CP & OH : 1.10 (w+fw)
(Which is inclusive of GST)
GST = 18%
GST applicable amount : 1.10 (w+ fw)/1.18 (Reverse calculation)
GST amount : 0.18 x 1.10 (w +fw)/1.18 which is equal to figure A above
f x w = 0.18 x 1.10 / 1.18 x w(1 + f)
or
f=0.1678 (1+f)
f-0.1678f=0.1678
0.8322f = 0.1678
f= 0.1678/0.8322
f=0.2016
Which is applicable for BSNL internal works (other than Quarters)
Regarding answer to Dilip Patil sir,
Basically BSNL does not frame any rules regarding this taxes and their applicability.
We have been being adopted the procedure laid down by CPWD only.
Previously they said CP & OH is not applicable on WCT and Service Tax, so we did not add.
But now they changed the procedure, so we have to.
If any circular is released by our C.O. in this regard, that may be quoted here.
I am attaching a circular of CPWD regarding rate analysis considering GST.