Invoice numbering rules in India under GST: series, characters and FY reset

Under Rule 46(b) of the CGST Rules, every tax invoice must carry a consecutive serial number of up to 16 characters, containing only letters, numbers, hyphens and slashes, that is unique for the financial year. You can run more than one series, you should not reuse cancelled numbers, and gaps or duplicates show up in GSTR-1 and, for larger businesses, get rejected by the e-invoice portal. This guide explains how to set up numbering that stays clean all year.

What Rule 46(b) actually says

The wording is short but every part of it matters. A tax invoice must contain "a consecutive serial number not exceeding sixteen characters, in one or multiple series, containing alphabets or numerals or special characters, hyphen or dash and slash symbolised as '-' and '/' respectively, and any combination thereof, unique for a financial year".

Break that into five requirements:

1. Consecutive. Each number in a series follows the previous one. 0041, 0042, 0043. Not 0041, 0045, 0042.
2. Not exceeding 16 characters. Count every character including slashes and hyphens.
3. One or multiple series. You may have as many series as you need, but each must be consecutive on its own.
4. Only letters, numerals, hyphen and slash. No spaces, no full stops, no underscores, no brackets, no hash symbol.
5. Unique for a financial year. No two invoices issued under the same GSTIN in the same April-to-March year may share a number.

The same wording is repeated for bills of supply (Rule 49), receipt vouchers (Rule 50), refund vouchers (Rule 51), payment vouchers (Rule 52), credit and debit notes (Rule 53) and delivery challans (Rule 55). So the rules below apply to all your GST documents, not just tax invoices.

Counting to 16: which formats fit

Because slashes and hyphens count, a format that looks compact can overflow once you add a year and a branch. Here is how common patterns measure up.

The safe pattern for most small businesses is a short prefix, a two-digit financial year pair, and a four- or five-digit padded number: INV/26-27/0042. That leaves room for a two- or three-letter branch or channel code if you later need one, as in KOL/26-27/0042.

Padding the number (0042 rather than 42) keeps the length constant and makes the list sort correctly in Excel. Five digits (00042) allows 99,999 invoices a year, which is more than enough for almost any business reading this.

Why the financial year belongs in the number

The rule only requires uniqueness within a financial year. That means INV-0042 in FY 2025-26 and INV-0042 in FY 2026-27 are technically two different, legal invoice numbers. In practice this causes problems:

• Your customer's accounts team sees two invoices from you with the same number and asks which one is which.
• A payment received in April against "invoice 42" cannot be matched without checking the date.
• If you are ever under e-invoicing, the IRN is a hash of your GSTIN, document type, document number and financial year, so the portal handles it, but your own reconciliation still has to.
• Search in any software becomes ambiguous.

Putting the year pair inside the number (26-27) removes the ambiguity at a cost of five characters. If you prefer a running number that never resets (100042, 100043, and so on across years), that is also fine and equally compliant; you just lose the at-a-glance year indicator.

Resetting on 1 April

On 1 April the financial year changes and you have a choice: restart at 0001 with a new year code, or keep counting. Either way, plan it before 31 March.

If you restart:

• Set the new series to INV/27-28/0001 for the first invoice dated on or after 1 April 2027.
• Invoices dated 31 March or earlier stay in the old series even if you print them on 2 April.
• Credit notes issued in April against March invoices belong to the new year's credit note series but reference the old invoice number.

If you continue counting, nothing changes on 1 April. Just make sure your GSTR-1 Table 13 for April reports the correct "from" number.

Do not change your series mid-year without a reason. If you must (for example, you moved to new software in September), close the old series at its last number, start the new one, and report both ranges in Table 13 for that month.

Multiple series: when they help and how to structure them

Rule 46(b) explicitly permits multiple series. Sensible reasons to use them:

• Separate document types. Tax invoices (INV), quotations (QT), proforma invoices (PI), delivery challans (DC), credit notes (CN) and debit notes (DN) should each have their own series. A quotation should never consume a tax invoice number.
• Separate branches under the same GSTIN. KOL/26-27/0042 and HWH/26-27/0042 are different numbers because the prefix differs.
• Separate sales channels. A retail counter (RT) and a B2B desk (B2B) that issue invoices independently.
• Exports versus domestic, since export invoices need extra fields and often a different template.

What multiple series do not allow is the same full string appearing twice. If your Kolkata and Howrah branches both use INV/26-27/0042, that is a duplicate even if two different people issued them. The prefix is what keeps them apart.

One series per GSTIN is a separate point. A business with registrations in West Bengal and Odisha has two GSTINs and each one runs its own series. A number issued under the Odisha GSTIN is not counted for the West Bengal one.

Cancelled numbers: what to do and what not to do

Every business cancels invoices: a customer changes the order before dispatch, a typo is spotted, a duplicate is raised by mistake. The rules are simple.

Do not reuse the number. If INV/26-27/0042 is cancelled, the next invoice is 0043. Reusing 0042 for a different sale means two documents with the same number exist, and one of them may already be with the customer.

Keep the cancelled document. Mark it "Cancelled" and retain it with your records. Section 35 requires you to keep records for 72 months from the due date of the annual return.

Report it in GSTR-1 Table 13. This table asks for, per document type and series: serial number from, serial number to, total number, cancelled, and net issued. A cancelled number is how you explain a gap.

If the invoice has already been reported or the goods have left, you cannot simply cancel. Issue a credit note for the full value and, if needed, a fresh invoice. The rules for that are in the credit note and debit note guide.

If you are under e-invoicing, an IRN can be cancelled on the portal within 24 hours of generation. After that, only a credit note works. The number itself is still consumed.

Why gaps and duplicates cause problems in returns

Officers and software both look at your invoice series to check that every sale has been reported. A series that runs 0041, 0042, 0044 with no cancelled 0043 in Table 13 raises the obvious question: where is 0043?

Three specific consequences:

1. GSTR-1 Table 13 mismatch. If the "net issued" count does not match the invoices you actually uploaded in Tables 4 to 7, the discrepancy is visible on the portal. It does not block filing, but it is a flag in scrutiny under Section 61.
2. Duplicates are rejected. The GSTR-1 upload rejects a document number that already exists for that GSTIN in that financial year. If the same number was used twice, one of the two sales cannot be reported until you fix it.
3. Buyer-side confusion. Your customer reconciles their purchases to their GSTR-2B by invoice number. A duplicate number on your side means their software matches the wrong document, and they may withhold payment until it is sorted out.

Date-based numbers (20260619-001) are legal but generate large gaps every day, because the "series" restarts each morning. Some officers accept this, some ask for an explanation. A single running series with the year is easier to defend.

A worked example: Bengaluru cloud kitchen with two channels

Tandoor Tales runs a cloud kitchen in Bengaluru with a single Karnataka GSTIN. It sells to individual customers through food delivery apps and also caters corporate lunches for registered companies. Here is how it sets up numbering for FY 2026-27.

Each string is under 16 characters (APP/26-27/0001 is 14). In June 2026 the kitchen issues corporate invoices INV/26-27/0031 to INV/26-27/0047, cancels 0039 because the event was postponed, and re-issues that order as 0048 when it happens. In GSTR-1 for June, Table 13 shows for tax invoices: from 0031, to 0048, total 18, cancelled 1, net issued 17. That matches the 17 invoices uploaded in Table 4, and the cancelled 0039 is retained in the file. No gap, no question.

On 1 April 2027 all five series restart at 0001 with the prefix changed to 27-28.

Common mistakes

1. Handwritten bill books with pre-printed numbers that collide with a software series. Pick one system, or give the bill book its own prefix.
2. Using the same series for quotations and invoices. Every quote that does not convert leaves a hole in your invoice series.
3. Spaces in numbers, as in "INV 26-27 0042". Many people do not notice until a GSTR-1 upload fails.
4. Exceeding 16 characters by adding a full four-digit year on both sides, a branch, and a product code.
5. Editing an issued invoice's number to close a gap. The customer already has the original; now two versions exist.
6. Forgetting Table 13 entirely. It is optional for some filers on the portal, but filling it consistently is the easiest way to explain gaps later.
7. Backdating an invoice into the previous year after the series has reset, which creates a number that was never in that year's range.

How VyaparKit helps

VyaparKit numbers documents in a financial-year series automatically, so an invoice created in FY 2026-27 gets the next consecutive number in the 26-27 series and the series resets on 1 April. The GST invoice, quotation, delivery challan and credit note tools each keep their own series, so a quotation never consumes an invoice number, and converting a quotation to an invoice assigns a fresh invoice number while keeping the link. Cancelled documents stay on record. VyaparKit does not file GSTR-1 for you; use the series information it shows when you fill Table 13.

Next steps

• Write down your series for every document type for FY 2026-27 and check each format is 16 characters or fewer.
• Search last year's invoices for duplicates or spaces in numbers and fix the pattern going forward.
• Decide whether to reset on 1 April or run a continuous number, and put a reminder in your calendar for 31 March.
• Start filling Table 13 in GSTR-1 every month if you do not already.
• Keep a "cancelled" folder, physical or digital, and never reuse a number.