Your GSTIN Arrived Last Week. The Invoices You Sent Before It Are Already Taxable.
Your GSTIN came through. Somewhere in the certificate is a line called effective date of registration, and for most freelancers it is not the date the certificate was issued. It is the date you became liable — the day your aggregate turnover crossed the threshold, possibly six or eight weeks earlier.
Everything you invoiced between those two dates was, in the eyes of the law, supplied by a registered person. You just didn't have a number to put on the paper yet. Those invoices went out with no GST on them, and the tax on them is now yours to pay.
There is a mechanism for this. It is called a revised invoice, it lives in Section 31(3)(a) of the CGST Act read with Rule 53, and you have one month from the date on your registration certificate to use it. After that the window shuts and you are paying the tax without any document that lets your client share the cost.
Most freelancers find this out from their CA in October, for a gap that opened in June.
Not tax advice. This explains how the revised-invoice mechanism normally works so you can act quickly and talk to your CA from an informed position. Dates and amounts change the answer — verify yours before you file anything.
Find your effective date first
Open your REG-06 certificate on the GST portal. There are three dates in play and people routinely confuse them:
- The liability date. The day your aggregate turnover crossed ₹20 lakh (₹10 lakh in special category states). Not the day you noticed. The invoice that pushed you over is the marker. If you're unsure whether you've crossed at all, or what counts toward the number, start here — exports and exempt income both count, which is what catches most people out.
- The application date. When you filed REG-01 and got an ARN.
- The certificate date. When REG-06 was actually granted and your GSTIN appeared.
Rule 10 then decides your effective date, and it only has two answers.
| When you applied | Effective from | What that means for your old invoices |
|---|---|---|
| Within 30 days of the liability date | The liability date | Registration reaches backwards. Everything from that day on is a taxable supply by a registered person — including the weeks you spent waiting on the portal. |
| After 30 days | The date registration was granted | Nothing before it becomes a registered supply. |
The second row sounds like the better outcome and mostly isn't. The period you spent liable-but-unregistered is its own exposure, assessable with interest and penalty. You didn't dodge anything. You moved it somewhere with fewer procedural tools.
The rest of this post is about the first case, because that's where the one-month clock is running.
What a revised invoice actually is
It is not a corrected invoice. This is the single most common misreading of the term.
If you sent an invoice with a wrong amount or a wrong GSTIN, the fix is a credit note or a debit note — there's a separate guide on that. GST law does not let you reissue an invoice to correct an error.
A revised invoice does one narrow job: it regularises invoices you issued in the window between your effective date and your certificate date, so the tax on them can be documented and — if your client is registered — claimed as credit.
That last part matters more than it sounds. The reason this mechanism exists at all is so your client can take input tax credit on a supply that was invoiced without tax. Without a revised invoice, you owe the GST and your client has nothing to claim. With one, the cost has somewhere to go.
What goes on it
A revised invoice carries everything a normal tax invoice carries under Rule 46 — your name and address, your new GSTIN, the client's details, description, value, tax rate and amount, place of supply, signature. If you want the full field list, it's in the GST invoice format guide.
On top of that, Rule 53 adds four things:
- 1.The words "Revised Invoice" must appear prominently, alongside the word "Supplementary" where applicable.
- 2.A consecutive serial number, unique for the financial year. Run these as their own series —
REV-001and upward — rather than folding them into your regular numbering. Rule 46(b) only asks for uniqueness within the financial year, so a separate series is entirely legal and much easier to explain later. The same logic applies if you're changing your number series mid-year. - 3.The date of issue of the revised invoice.
- 4.The number and date of the original invoice it revises. This is the link that makes the document work. One revised invoice per original invoice, referencing it explicitly.
If some of those gap invoices went to clients who aren't GST-registered — individuals, or small businesses below the threshold — you can issue a single consolidated revised invoice covering all supplies to that recipient in the period, rather than one per invoice.
Now the awkward part: who pays the eighteen percent
You invoiced ₹1,50,000 in July with no GST. The client paid ₹1,50,000. Your certificate arrives in September with an effective date of 2 July. That supply now carries ₹27,000 of tax.
You have two honest routes.
| Ask the client for it | Absorb it | |
|---|---|---|
| Taxable value | ₹1,50,000 | ₹1,27,119 |
| GST at 18% | ₹27,000 | ₹22,881 |
| Invoice total | ₹1,77,000 | ₹1,50,000 |
| You keep | ₹1,50,000 | ₹1,27,119 |
| Client's real cost | Unchanged, if they're registered | Unchanged |
Ask the client for it. Issue the revised invoice for ₹1,50,000 plus ₹27,000 GST, and ask for the balance. If your client is GST-registered, this is a genuinely reasonable ask — the ₹27,000 becomes input tax credit for them, so their real cost is unchanged. That is precisely the situation the revised invoice was designed for, and a client with a competent accounts team will recognise the document for what it is. Explain it in one line: my GST registration was granted with effect from 2 July, so this invoice needed to be reissued as a tax invoice; the GST is fully creditable to you.
Absorb it. Treat the ₹1,50,000 you already received as tax-inclusive and gross down. The taxable value becomes ₹1,27,119 and the GST ₹22,881. You keep less, the client is undisturbed, and you don't have an uncomfortable conversation. Section 15 values a supply at the price actually paid, so this is a defensible position — but confirm the treatment with your CA before you commit a whole quarter's invoices to it, because it changes your declared turnover as well as your tax.
Which one you choose usually depends on the client, not the law. Registered client with a finance function: ask. Individual who paid from a personal account and has gone quiet: absorb.
Either way, do it inside the month. Once the window closes the tax is still due — you've just lost the only document that could have moved it.
If your gap invoices were exports, this gets worse
Here is the part nobody writes about, and it's the one that hits freelancers billing abroad hardest.
Say you crossed the threshold on foreign income. Aggregate turnover includes zero-rated exports, so a freelancer billing entirely in USD can be pushed over ₹20 lakh without ever charging a rupee of GST to anyone. You register. Your effective date backdates to June. Your GSTIN arrives in August.
Exports of services are zero-rated, so in principle the gap invoices carry no tax. But zero-rating without paying IGST requires a valid LUT — and an LUT cannot be filed before you have a GSTIN, and it cannot be backdated. A Letter of Undertaking runs from its filing date to 31 March. There is no provision to make it reach behind itself.
So your June and July export invoices sit in a period where you were a registered person making zero-rated supplies with no LUT on file. The default treatment for a zero-rated supply without an LUT is export with payment of IGST, refundable under Rule 96. On ₹6 lakh of export invoices in the gap, that's ₹1,08,000 out and then reclaimed — a refund cycle that commonly runs two to six months.
There's a second view, and it has support: that a missing LUT is a procedural lapse rather than a substantive failure, particularly where the export genuinely happened and the foreign exchange was realised. Some practitioners regularise the period on that basis without routing money through the IGST-and-refund cycle. It is not a position to adopt from a blog post. It is a position to put to your CA with the actual dates and amounts in front of them.
What is not in dispute: file the LUT the same day your GSTIN arrives. Not the same week. The gap between certificate and LUT is a second, entirely avoidable window of uncovered exports layered on top of the first one. The LUT filing walkthrough takes about ten minutes and the ARN is generated instantly, so there is no reason for that date to slip.
Reporting the gap in your first return
Your first GSTR-1 and GSTR-3B cover everything from the effective date, not from the day your GSTIN was issued. The intervening supplies belong in that first return.
Report the revised invoices as the outward supplies. Your original gap invoices — the ones with no tax on them — don't get separately reported; the revised invoice is the document of record for that supply. Where you've issued a consolidated revised invoice to unregistered recipients, it goes in as a single B2C entry.
Get this wrong in the first return and you're amending it later. Amendments of a financial year's outward supplies have their own deadline, and it arrives sooner than most freelancers assume.
What to do this week
- 1.Pull your REG-06 and write down the effective date. Then list every invoice you issued from that date until the certificate date.
- 2.Count the days since the certificate was issued. That number against thirty tells you how much of the window is left.
- 3.Split the list: registered clients, unregistered clients, exports. Different treatment for each.
- 4.If there are exports on the list, check whether your LUT is filed. If it isn't, file it today and treat the gap exports as a separate conversation with your CA.
- 5.Send the revised invoices with one line of explanation each. Most clients accept this without friction once they understand the credit is theirs to take.
The invoices that come after the gap
Closing the gap is a one-month job. Getting the next two hundred invoices right is the part that repeats.
That's most of what Mavoin does. Once your GSTIN is on your profile, every invoice carries the CGST/SGST or IGST split, the place of supply, and — for exports — the LUT declaration, without you deciding any of it per invoice. A revised-invoice series is just a number series, so it follows the same Rule 46(b) rules as your regular one: your own prefix, your own starting number, consecutive for the year.
₹199/month after the trial, and your data stays exportable.
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Sources: Section 31, CGST Act 2017 (CBIC) · Rule 10, CGST Rules 2017 (CBIC) · Rule 53, CGST Rules 2017 (CBIC)
Mavoin is not a Chartered Accountant service. General information, current as of September 2026.
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Start 30-day trialFrequently asked questions
Can I just add the GST to my next invoice instead?
No. GST attaches to each supply at its own time of supply. Loading a later invoice with tax belonging to an earlier one misstates both, and it won't survive a reconciliation between your returns and your client's.
What if the one-month window has already closed?
The tax remains payable. You've lost the prescribed document for passing it on, so in practice you absorb it and declare the supplies in your return. Speak to your CA before deciding how to present the period — the options narrow but they don't vanish.
My client refuses to pay the extra GST. Now what?
Treat the amount received as tax-inclusive and gross down. You bear the tax, but the supply is correctly declared and your return is clean. It's a commercial loss, not a compliance one.
Do I issue revised invoices for invoices sent before my effective date?
No. Supplies made before you became liable to register are outside GST entirely. There is nothing to revise. That period stays exactly as it was — a non-GST invoice, correctly issued at the time.
Does the revised invoice replace the original, or sit alongside it?
Alongside. The original stays in your records and the revised invoice references it by number and date. Don't delete or renumber anything.
I registered voluntarily, before crossing any threshold. Does this apply to me?
Voluntary registration takes effect from the date registration is granted, so there's generally no backdated window and nothing to revise. Confirm the effective date on your own certificate rather than assuming.
Does the client's input tax credit have a deadline?
Yes, and it runs on the original supply's financial year — not on the date you issued the revised invoice. Another reason not to sit on the one-month window.