Inconsistent Summary Tax Handling in Purchase Invoice (isSOTrx = N) – iDempiere 12,GST setup (India)

[Nisha John]

Hello Team,
I would like to report a possible inconsistency in summary (parent-child) tax handling in iDempiere 12.
Parent tax: SGST+CGST 18% (Summary Level = Y)
Child taxes: SGST 9% and CGST 9% (linked to parent)
Sales Invoice (isSOTrx = Y):
Parent tax explodes correctly
Two child tax lines (9% + 9%) are created in C_InvoiceTax
Amounts are calculated correctly
Purchase Invoice (isSOTrx = N):
Child tax lines are created in C_InvoiceTax
However, the full 18% amount is applied to each child
Instead of splitting correctly into 9% + 9%
It appears related to the logic in MInvoiceTax.calculateTaxFromLines():
if (!documentLevel && amt.signum() != 0 && !isSOTrx) // manually entered
;
else if (documentLevel || baseAmt.signum() == 0)
amt = Env.ZERO;
else // calculate line tax
amt = tax.calculateTax(baseAmt, isTaxIncluded(), getPrecision());
//
taxAmt = taxAmt.add(amt);
Because of the !isSOTrx condition, recalculation is skipped for Purchase invoices when an amount is already present, leading to incorrect distribution of summary tax.
From a GST perspective, consistent splitting is expected.

[Shiju TP]

In Purchase Transaction in order to match with Vendor Invoice, tax is not calculated by calling tax.calculateTax

In Indian context Tax is split between Federal/Union/Central government   and  State/Regional government

For example SGST/CGST-18% is a parent tax which is split between the 2 governments  as follows

SGST 9% is Paid To  by State/Regional Goverment

CGST 9% is Paid To  by Central/Federal/Union Goverment

This is applicable in both Purchase and Sales Transaction

But because of the below code

 if (!documentLevel && amt.signum() != 0 && !isSOTrx) // manually entered

the splitting of Tax into 2 Child Tax is blocked in Purchase Transaction which is a bug  or oversight

How To:

1) Create a Parent Tax 

    

   SGST+CGST-18%  Rate is 18% and  set True as Summary / Parent

2) Create 2 Child Tax

     

  SGST-8%  Rate is 8% and set SGST+CGST-18% as Parent Tax 

  CGST-8% Rate is 8% and set SGST+CGST-18% as Parent Tax

3 Create a Tax Category GST-18% and assign to a Product PlumTree

4) Now create a Purchase Invoice / Vendor Invoice for the Plum Tree  

5) Now create a Sale Invoice / Customer Invoice for the Plum Tree  

6) Process the both Purchase Invoice and Sales Invoice and check Tax Invoice Tab of both Invoices

 7) In Purchase Invoice Tax calculation is wrong     18% SGST + 18% CGST  = 36%

8) In Sales Invoice Tax Calculation is right    8% SGST + 8% CGST  = 18%