Why the HSN summary in GSTR-1 is the table most likely to be quietly wrong, how to check it in a minute, and what a mismatch costs you later.
What Table 12 is for
Tables 4 to 9 of GSTR-1 say who you supplied and what tax you charged. Table 12 says what you supplied, grouped by HSN code and rate. They describe the same month from two directions, so their totals have to agree.
From the May 2025 return period Table 12 is split into two halves, one for supplies to registered buyers and one for everything else. The split changed the shape of the table; it did not change the rule that the two halves together must account for every outward supply.
Why it goes wrong so often
Most tools build the return section by section. B2B invoices come from one path, the B2C aggregate from another, credit notes from a third. If the HSN summary is built from only one of those paths, it comes out short, and nothing in the file says so: the JSON is well formed, the portal accepts it, and the summary the portal generates looks reasonable at a glance.
We have seen a real filed return where Table 12 covered 580.58 rupees while the liability tables carried 3,614.45. The 3,033.87 rupee gap was the entire B2C half of the month.
How to check yours in under a minute
Add up the taxable value across Tables 4A, 5, 6 and 7, then subtract the taxable value of every credit note in Table 9B. Add up the taxable value in both halves of Table 12. The two figures should be identical, to the paisa.
- Tables 4A + 5 + 6 + 7, less Table 9B credit notes
- compared against Table 12 B2B + Table 12 B2C
- difference should be exactly zero, not approximately zero
What a mismatch costs
Nothing happens immediately, which is the problem. The gap surfaces when the annual return is prepared and the HSN summary for the year does not tie to the turnover already declared, or when a notice asks for a reconciliation you now have to construct from twelve months of marketplace files.
Fixing it in the month it happens costs a few minutes. Fixing it in year three costs a professional fee and a written explanation.
How fynxIQ handles it
Table 12 is derived from the whole ledger and then asserted against the sum of every other outward table, in integer paise, with no tolerance. If the difference is not exactly zero, the return cannot be downloaded and the app names the amount and the rows behind it.
Try it on your own figures with the free HSN code checker.
Which file to download, and from where: the list for each marketplace and the GST portal.
By Raunak Pathak, founder of fynxIQ, who files GST returns on it. Last updated 30 August 2026. This is general information about how GST returns work, not advice about your particular return.