The monthly GSTR-3B checklist for a small business

Nine checks to run before you submit GSTR-3B: sales match, credit match, ineligible credit reversed, tax paid from the right ledger, then file and keep the proof.

Before you submit GSTR-3B, check nine things. Your sales match GSTR-1. Your credit matches GSTR-2B. Ineligible credit is reversed. Every sale is in the right tax head and the right period. You know what you owe, you pay it from the right ledger, you file with the right signature, and you keep the proof. GSTR-3B cannot be revised once filed, so the checking happens before you submit, not after.

Last reviewed: October 2026. Return periods, due dates, late fees and interest, and how much of a pre-filled GSTR-3B you can edit are set by GST law and the portal, and they change. Confirm the current position for your business on the GST portal or with your CA.

What is GSTR-3B and what does it settle?

GSTR-3B is the summary return in which you report the period's sales, claim your input tax credit, and pay the tax that is left. Unlike GSTR-1, it does not list invoices one by one. It gives totals, by table.

It is also the return where money moves. The tax you owe is paid through your electronic ledgers when you file. A GSTR-1 can be corrected after filing. A GSTR-3B generally cannot be revised, so an error carries forward into a later period.

This is why the order of work matters. Sales go into GSTR-1 first, credit is reconciled next, and GSTR-3B comes last, built on both.

1. Do your sales in GSTR-3B match GSTR-1 and your sales register?

Check this first. The portal can pre-fill your outward supply values from the GSTR-1 you filed, so any gap between GSTR-1 and your books can travel into GSTR-3B. Check the current portal process with your CA.

Take the period's sales register and compare three things: taxable value, tax charged, and the split between intra-state and inter-state sales. They should agree with GSTR-1 and with the GSTR-3B tables. Credit and debit notes raised in the period should be inside these numbers.

If they do not agree, find the cause before filing. The usual ones are a bill left out of GSTR-1, a bill in the wrong table, or a note not booked. See how to file GSTR-1 straight from your sales records, including how to correct it before GSTR-3B goes in.

2. Does the credit you claim match GSTR-2B?

The credit you claim should come from your purchase register, checked against GSTR-2B, and not from the pre-filled figure alone. GSTR-2B shows what your suppliers have reported. Your register shows what you have received and hold bills for.

Match the two, list the differences, and decide for each: claim it, hold it, or reverse it. The full method is in how to reconcile GSTR-2B with your purchase register.

Do this well before filing day. A supplier who needs to report a missed bill needs time, and a call on the last evening rarely fixes anything.

3. Have you reversed credit you are not entitled to?

Credit that GSTR-2B shows as available can still be ineligible, and you are the one who has to reverse it. Common cases are purchases on which the law blocks credit, goods or services used partly for exempt or non-business purposes, and bills not paid within the period the law allows.

Go through the period's purchases with one question: is there any bill where I should not take the full credit? Enter the reversal in the table the portal provides, and keep a note of the bill and the reason.

The rules on what is blocked and when credit is lost are in input tax credit: when you get it and when you lose it. Confirm the current rules with your CA.

4. Is every sale in the right tax head?

Check that intra-state sales carry CGST and SGST, and inter-state sales carry IGST. A bill with the wrong head shows up as a mismatch in your buyer's statement, and as a payment in the wrong ledger on yours.

The head follows the place of supply on the bill, not the buyer's address on a visiting card. If a bill looks wrong, check the place of supply first.

If you are unsure how the head is decided, see CGST and SGST or IGST: how to decide, every time.

5. Is every bill in the right period?

For most sales, the invoice date decides which month a bill belongs to. The time-of-supply rules have exceptions, so ask your CA about any bill raised well after delivery or payment. Bills raised late, or entered late, are the usual cause of a total that is out by a few documents.

Run your sales register for exactly the period, and check the first and last bill numbers against your invoice series. Cancelled bills should be marked cancelled, not deleted, so the series has no unexplained gaps.

The same applies to purchases. A bill dated in an earlier period does not become a current-period bill because it arrived late. Ask your CA how a late bill is to be treated.

6. Do you know what you owe, and what you will pay in cash?

Work out the figure before you open the payment screen. Your output tax for the period, less the credit you are entitled to use, gives the tax payable. Credit in the electronic credit ledger is used against your liability in the order the law sets. What the credit does not cover is paid from the electronic cash ledger.

So the question is whether the cash ledger holds enough. If it does not, you will have to make a challan payment first. That takes time, so plan for it earlier than you think you need to.

Which credit can pay which tax is fixed by law. Ask your CA if you are unsure.

7. Are you paying from the right ledger, and is the payment complete?

Payment is part of filing GSTR-3B. Before you submit, check the payment summary: how much is set off from the credit ledger, how much from the cash ledger, and whether the totals agree with your working.

Do not guess. Tax paid late can carry interest, and the rules for that are on the portal.

Keep the working on one sheet: output tax by head, credit used by head, cash paid by head. That sheet is your answer if the department ever asks how the return was built.

8. Are you filing with the right signature, in time?

Submitting the return and filing it are separate steps. After you submit, you file with a digital signature certificate or an electronic verification code, as applicable to your type of registration. Make sure the person who holds the signature is available.

The due date depends on your return scheme and is set by notification. Look up the current date on the portal, not in an old calendar, and plan to file a day or two early. Late filing can attract a fee and interest. Confirm the current amounts with your CA.

9. Have you kept the proof?

The filed return is not enough. Keep what shows how it was built: the sales register, the purchase register, the GSTR-2B you reconciled against, the reversal note, the payment working, and the acknowledgement of filing.

Save them together, with the period in the file name. When a notice or a query comes, you can answer from one folder, not from memory.

Run the same checklist every month. A routine catches the same kinds of mistakes early, and the month you skip it is the month the error appears.

FAQ

What is GSTR-3B? GSTR-3B is the summary return a registered business files on the GST portal for each return period. It reports your outward supplies, the input tax credit you claim, and the tax you pay. It is a summary, not an invoice-wise return, and the tax payable is settled when you file it.

Can I change the figures the portal pre-fills in GSTR-3B? It depends on the table and on the portal's current rules, which have changed over time. Do not plan to fix figures at filing. Reconcile your sales and purchases first, so the pre-filled values are already right, and check the portal's current advisory or ask your CA about what can still be edited.

What happens if I file GSTR-3B with a mistake? Once filed, GSTR-3B cannot be revised. A mistake is usually corrected in a later period's return, along with any interest or other consequence that applies to your case. Check the correction route that fits your mistake with your CA, and keep the working that shows what you corrected and why.

If you would rather your month-end workings came out of the bills you already raised, see how KillStock prepares GST return workings from your documents and what it costs.