How to file GSTR-1
For anyone filing their own returns, or checking what their accountant filed.
GSTR-1 is the statement of what you sold. It is where your outward supplies are declared, invoice by invoice for B2B and in summary for B2C, and it is what your customers' input tax credit is built from - which is why an error here becomes their problem as well as yours.
What actually goes in it
GSTR-1 reports outward supplies for the period. B2B sales are reported invoice by invoice, with the customer's GSTIN, the invoice number and date, the taxable value and the tax. B2C sales are reported in summary, except for large inter-state B2C invoices, which are reported individually.
Also in it: credit and debit notes, exports, nil-rated and exempt supplies, advances received, and an HSN-wise summary of what you sold.
When it is due
Monthly filers file by the 11th of the following month. Businesses on the QRMP scheme - broadly, smaller turnovers that have opted in - file quarterly, by the 13th of the month after the quarter, while still paying tax monthly.
Due dates get extended by notification more often than anyone would like. Check the portal before you rely on a date you remember.
Filing it on the portal
The portal accepts a JSON file prepared by your accounting software, which is how most businesses with more than a handful of invoices do it. Typing invoices directly into the portal is possible and is a reasonable choice if you raise five bills a month.
- 1Prepare the JSON from your books for the return period.
- 2Log in at gst.gov.in and go to Returns Dashboard, then choose the financial year and the period.
- 3Open GSTR-1 and choose Prepare Offline, then Upload.
- 4Upload the JSON and wait for the processing status. Errors come back against the specific invoices that caused them.
- 5Go back to Prepare Online and check the tables - the counts and totals should match your own sales figure for the period.
- 6Submit, then file with DSC or EVC.
The mistakes that cost money later
Almost every GSTR-1 problem is one of a small handful, and all of them are easier to prevent than to correct.
- An inter-state sale billed as intra-state, or the reverse. The tax split is decided by place of supply, and getting it wrong means the return will not agree with the invoice you gave the customer.
- A wrong or missing GSTIN on a B2B invoice - the customer will not see the credit, and will call you in a few weeks.
- Invoice numbers that repeat, or a series that resets mid-year. The number must be unique within the financial year.
- Credit notes left out, which overstates your outward supply and the tax on it.
- The HSN summary not agreeing with the invoice lines, usually because HSN was typed per invoice rather than kept on the item.
How Zembook handles it
GSTR-1 is computed from the sale vouchers you already entered and exports as portal-ready JSON, so there is no second place to keep in step - correcting an invoice corrects the return. The tax split follows from the place of supply rather than being chosen by hand, and HSN lives on the item so the summary cannot drift from the lines.
Zembook produces the file; you upload it. It does not file on your behalf, and no software should claim to without holding your portal credentials.
Reviewed August 2026. This describes general GST practice and is not tax advice. Thresholds, due dates and rules change by notification, and several vary by state — confirm anything that decides a filing on gst.gov.in or with your accountant.
Questions people ask
- Can I revise a GSTR-1 after filing?
- No - a filed GSTR-1 cannot be revised. Corrections are made in a later period's return by amending the invoice there, and there is a cut-off after which amendments for a financial year are no longer allowed. That is why the checks before submitting matter.
- Do I have to file GSTR-1 if I had no sales?
- Yes. A nil return still has to be filed, and there is a simplified nil filing route on the portal.
- What is the late fee?
- There is a per-day late fee with a cap, and it differs for nil returns. The amounts are changed by notification, so check the current figures on the portal rather than trusting a number from an article.
Zembook does this part for you
GSTR-1 and GSTR-3B as portal-ready JSON computed from your own vouchers, GSTR-2B reconciliation against your purchases, reverse charge reported separately, e-Way Bill and e-Invoice files.