Two returns, filed by the same business, for the same month, describing the same sales. It is a fair question why both exist — and the answer explains most of what goes wrong with GST compliance in a small business.
GSTR-1 is a statement. GSTR-3B is a payment.
GSTR-1 is where you declare your outward supplies, invoice by invoice. It is detailed: every B2B invoice with the buyer's GSTIN, B2C sales in summary, credit and debit notes, exports, and an HSN-wise summary of what you sold. Nothing is paid when you file it.
GSTR-3B is the summary return where the money actually moves. Total outward tax, total input tax credit claimed, and the net amount you pay in cash. It is short — a single page of totals.
So GSTR-1 tells the department what you sold, and GSTR-3B settles what you owe. Both describe the same month, from two directions.
Why the matching matters more than the filing
Here is the part most business owners discover late: your GSTR-1 is not really for the department. It is for your customer.
When you file GSTR-1, every B2B invoice in it flows into your buyer's GSTR-2B — the statement that tells them how much input tax credit they are allowed to claim. If you have not filed, your invoice is not there, and your buyer cannot claim credit on a payment they have already made to you.
That is why a good buyer's accounts team chases you around the 12th of every month. They are not being difficult. Your delay is sitting on their working capital.
The three gaps that cause trouble
Reconciliation sounds like an accounting chore until you know what you are actually looking for. There are three gaps, and they mean different things.
1. GSTR-1 higher than GSTR-3B. You declared sales you did not pay tax on. Sometimes it is a genuine timing difference — an invoice raised on the 31st, recorded in the next period's 3B. Left uncorrected across months, it reads as under-payment.
2. GSTR-3B higher than GSTR-1. You paid tax on sales you did not declare invoice-wise. Less dangerous for you, but your buyers are missing credit they are entitled to, and they will find out.
3. Input credit claimed in 3B that is not in your 2B. This is the expensive one. Credit is restricted to what actually appears in your GSTR-2B — meaning a supplier who has not filed their GSTR-1 has effectively cost you that credit until they do. Claiming it anyway creates a liability with interest.
A reconciliation routine that takes ten minutes
You do not need software to do this well, but you do need to do it every month rather than every year.
- Before filing 3B, total your GSTR-1. Outward taxable value and tax should equal what you are about to declare in 3B. If they do not, find out why now, while you still remember the invoice.
- Download GSTR-2B and compare it to your purchase register. Anything in your books that is not in 2B is credit you cannot take this month. Make a list and chase those suppliers.
- Keep a running difference sheet. One row per month, three columns: declared, paid, credit taken. A year of that sheet answers a departmental query in minutes instead of weeks.
- Reconcile annually against your books before the annual return, not during it.
Where this goes wrong in practice
Almost every reconciliation problem we see in Kaushambi has the same root cause: invoices are raised on paper or in a plain billing app that does not produce a GSTR-1 summary, so the return is assembled from memory at the last minute. The numbers are close enough to file and wrong enough to fail scrutiny two years later, when nobody remembers the transaction.
Software fixes this by construction: if every invoice is raised in the same place, the summary is not assembled at all, it is just read.
That is exactly why we built BizGST Pro — invoices in, GSTR-1 and 3B summaries out, exportable as CSV for your CA. But the discipline matters more than the tool. A monthly difference sheet in a notebook beats sophisticated software nobody opens.
If you have already fallen behind
Late returns compound: fees accrue, buyers stop ordering, and credit gets blocked. It is recoverable, and the sooner it is dealt with the cheaper it is. Our GST and tax desk handles exactly this — bringing lapsed filings current, reconciling the difference, and answering the notice if one has already arrived.
This is general information, not tax advice. GST rules and rates change; have your chartered accountant confirm the treatment of your specific transactions before filing.