Key takeaways
What this article covers, in order:
- Start with the certificate, not the invoice book
- What about sales made before the certificate arrived?
- Monthly or quarterly? Pick before the first due date
- Set up your books before you raise invoice number one
- Your first GSTR-1
- Your first GSTR-3B
The approval email lands, you download the certificate, and for about ten minutes you feel very official. Then the question hits: what am I supposed to file, and by when? Short answer: your first GSTR-1 and GSTR-3B are due for the tax period in which your registration takes effect, even if you didn't sell a single thing. Here's how to get from GSTIN to a clean first filing without the usual panic.
Start with the certificate, not the invoice book
Open your registration certificate (Form REG-06) and look for two dates. They're not the same, and the difference matters more than people think.
The effective date of registration is when your GST liability starts. The date of issue is when the department actually approved you. If you applied within 30 days of crossing the threshold, the effective date is usually the day you became liable, which can be a couple of weeks before the certificate arrived.
While you're there, check the boring stuff: legal name, trade name, principal place of business, any additional godowns or shops. A missing additional place of business will bite you later when you generate e-way bills or receive a notice at the wrong address. Fix it now through a non-core amendment.
One more thing on the certificate: it tells you whether you're a regular taxpayer or under composition. This post is for regular taxpayers, the ones who file GSTR-1 and GSTR-3B. Composition dealers have a different rhythm (CMP-08 and GSTR-4).
What about sales made before the certificate arrived?
Take Anjali, who started a home-décor business in Jaipur. Her effective date is 2 Sep 2026, but the certificate is issued on 18 Sep 2026. In those 16 days she billed ₹1,80,000 to a few boutiques, on plain invoices without a GSTIN.
Those sales were taxable. The law lets her issue revised tax invoices for that gap, within one month of the date the certificate was issued. So by 18 Oct 2026 she should send the boutiques proper tax invoices, and those go into her first GSTR-1. Her buyers get their input tax credit, and she isn't under-reporting her first period.
Monthly or quarterly? Pick before the first due date
If your aggregate turnover is up to ₹5 crore, you can file under QRMP (Quarterly Return, Monthly Payment). Otherwise it's monthly. Here's how the two compare:
| Monthly filing | QRMP (turnover up to ₹5 crore) | |
|---|---|---|
| GSTR-1 | By the 11th of the next month | By the 13th after the quarter (optional IFF for B2B invoices in months 1 and 2, also by the 13th) |
| GSTR-3B | By the 20th of the next month | By the 22nd or 24th after the quarter, depending on your state |
| Paying tax | With each GSTR-3B | PMT-06 challan by the 25th for months 1 and 2, the rest with the quarterly 3B |
| Returns a year | 24 | 8, plus monthly payments |
The portal puts new registrants on a default option based on what you declared. You can see and change it under Returns, "Opt-in for Quarterly Return", within the windows it allows.
So which one? If your customers are mostly other businesses, they'll want your invoices showing up in their GSTR-2B every month. Monthly filing, or QRMP with IFF, keeps them happy. If you sell mostly to consumers and volumes are small, QRMP saves you a lot of evenings.
Set up your books before you raise invoice number one
Resist the urge to just start billing. Fixing a setup mistake across forty invoices later is miserable.
Pick an invoice series that's unique for the financial year, something like INV/26-27/001. GST expects consecutive numbers, up to 16 characters.
Map every product or service to its HSN or SAC code. Smaller businesses (turnover up to ₹5 crore) generally show 4-digit HSN on B2B invoices, larger ones 6 digits, but check the current requirement on the portal before you lock it in.
Then get the rates right. After the rate rationalisation that took effect on 22 Sep 2025, most goods now sit at 5% or 18%, with 40% for a small set of demerit goods. If you're copying rates from an old price list or a supplier's 2024 invoice, double-check every line.
And collect customer GSTINs before you bill. A B2B invoice without the buyer's GSTIN ends up reported as B2C, and your customer loses the credit. They'll call you about it, usually on the 19th.
The place-of-supply trap
Selling within your state? CGST plus SGST. Selling to someone in another state? IGST. Sounds simple. Yet charging CGST + SGST on an inter-state sale is easily the most common error we see on first returns. Correcting it means a credit note and a fresh invoice, and the tax you paid under the wrong head has to be sorted out separately.
Your first GSTR-1
GSTR-1 lists what you sold. For the first period, you'll report B2B invoices from the effective date (revised ones included), B2C sales (large inter-state ones individually, the rest summarised by rate and state), any credit or debit notes, exports or SEZ supplies if you made any, and two tables people often forget: the HSN summary and the document summary.
Made no sales? File a nil GSTR-1 anyway. It takes a minute. Skipping it blocks your GSTR-3B and racks up a late fee for nothing.
Your first GSTR-3B
This is the one where money moves. Your output tax in Table 3.1 is auto-filled from GSTR-1, so review it rather than retyping it.
Input tax credit comes from GSTR-2B, which the portal generates around the 14th of the following month. In month one, your 2B might look thin because your suppliers haven't all filed. That's normal. Claim only what's actually in 2B and genuinely eligible; the rest can come in a later month once it appears.
There's also a provision worth knowing about. If you applied within 30 days of becoming liable, you may be able to claim ITC on inputs you held in stock the day before your effective date, using Form ITC-01. It has its own conditions and a time limit, so it's worth a ten-minute call with your CA before you decide.
If there's tax to pay in cash, create a challan on the portal, pay by net banking or UPI, and offset it in 3B. Pay late, and Section 50 interest at 18% a year kicks in on the cash portion. The late fee is ₹50 a day (₹20 for a nil return), subject to caps based on turnover.
A practical tip: the portal slows to a crawl on the evening of the 20th, because half of India files then. If you can file on the 17th or 18th, do.
Your first-period checklist
- [ ] REG-06 downloaded; effective date and issue date noted
- [ ] Revised invoices issued for sales between those dates, within one month of issue
- [ ] Filing frequency confirmed (monthly or QRMP)
- [ ] Invoice series, HSN/SAC codes and current GST rates set up
- [ ] GSTINs collected for every B2B customer
- [ ] Purchase bills saved with supplier GSTINs
- [ ] GSTR-2B checked once it's generated
- [ ] GSTR-1 filed (nil if no sales)
- [ ] Tax paid and GSTR-3B filed before the due date
- [ ] ITC-01 for opening stock discussed with your CA
Mistakes we see in first returns
Counting from the certificate date instead of the effective date is the big one. Your liability starts on the effective date, full stop.
Next is not filing because "there was nothing to file". A nil return is still a return, and an unfiled period holds up the next one.
Then there's claiming ITC on a bill that isn't in GSTR-2B. It feels like your credit. But if your supplier hasn't filed, the portal won't back you up, and you'll be reversing it with interest later.
How HelloBooks helps
HelloBooks Free lets a newly registered business file GSTR-1 and GSTR-3B for one GSTIN directly to the GST portal from inside HelloBooks, at ₹0, with no credit card and no expiry. You raise invoices with HSN/SAC codes and the right CGST/SGST/IGST split, record purchase bills, and reconcile against GSTR-2B so you know which credits are safe to claim. Before you file GSTR-3B, you'll see the interest and late fee exactly as the GST portal calculates them. You can invite your CA into the same books to look over your first return. Free covers up to 200 transactions a year and 2 users; the pricing page shows what's on the paid plans if you outgrow that. Here's how the GSTR-1 filing and GSTR-3B filing flows work.
FAQs
Do I have to file for the month I got registered?
Yes. Returns start from the tax period in which your effective date falls. Registered on 25 Sep 2026? Your first returns cover Sep 2026, or the Jul–Sep 2026 quarter under QRMP.
I made no sales in my first month. Still need to file?
Yes, a nil GSTR-1 and a nil GSTR-3B. The late fee on nil returns is lower, but it's not zero.
Can I claim ITC on purchases made before registration?
Sometimes. If you applied within 30 days of becoming liable, you may claim ITC on inputs held in stock the day before your effective date through ITC-01. Capital goods and services follow different rules, so check with a CA.
I billed customers before my GSTIN came through. What now?
Issue revised tax invoices for those sales within one month of the certificate's issue date, and report them in your first GSTR-1.
Should a new business choose QRMP?
If turnover is up to ₹5 crore and most customers are consumers, QRMP cuts the paperwork. If business buyers depend on your invoices for their credit, go monthly or use QRMP with IFF.
That first return is the hardest one. After two or three cycles it becomes a routine you can do over a cup of tea.
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