GST Invoice Number Series Rules: How to Number Invoices Correctly

Invoice numbering looks like housekeeping, but under GST it is a legal requirement with a precise rule behind it. Get it wrong and you may face rejected e-invoices, mismatched returns or awkward questions about gaps in your sequence.

This guide explains Rule 46(b) in plain terms, shows how to design a series for single and multi-branch businesses, and covers the edge cases: cancelled numbers, year-end, credit notes and challans. General numbering habits that apply outside GST are covered in invoice numbering best practices.

What exactly does Rule 46(b) say?

Rule 46(b) requires a tax invoice to carry:

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 tests:

Test	What it means in practice
Consecutive	Numbers run in sequence (0001, 0002, 0003) without arbitrary jumps
Max 16 characters	Count every character, including prefixes, hyphens and slashes
One or multiple series	You may run separate series for branches, counters or document types
Allowed characters	A–Z, a–z, 0–9, hyphen (-), slash (/) only
Unique for a financial year	No number may repeat within 1 April to 31 March for the same GSTIN

The same wording appears in Rule 49 (bills of supply), Rule 53 (revised invoices, credit and debit notes) and Rule 55 (delivery challans), so every GST document you issue follows the same standard.

How do you count the 16 characters?

Every character counts. Take these examples:

Invoice number	Characters	Valid?
INV/26-27/0001	14	Yes
PUN-26-27-00451	15	Yes
2627/00001	10	Yes
MUM/RETAIL/2026-27/001	22	No: too long
INV#2026-001	12	No: "#" not allowed
INV 26-27 001	13	No: spaces not allowed
inv_0001	8	No: underscore not allowed

A common trap is a template that adds a full four-digit year plus a branch name plus a five-digit counter. That easily crosses 16. Use two-digit year codes and short branch codes.

How should you design an invoice number series?

A good series has three parts: a short prefix, a year code and a running counter.

1. Prefix (2–4 characters): identifies the document type or branch, such as INV, BOS, CN, DN, DC, or a branch code like PN for Pune.
2. Year code (5 characters): such as 26-27 for FY 2026-27.
3. Counter (4–6 digits): zero-padded, such as 00001.

Join them with slashes or hyphens: INV/26-27/00001 is 15 characters and leaves room.

Planning counter length

Estimate your peak yearly volume and add a margin:

• Up to 9,999 invoices a year: 4-digit counter
• Up to 99,999: 5-digit counter
• More: 6 digits, with a shorter prefix

Worked example: a multi-branch, multi-document setup

A Surat textile trader with one GSTIN in Gujarat has a head office and two shops, and issues tax invoices, bills of supply, credit notes and delivery challans. It expects around 18,000 invoices a year across all locations.

Document	Location	Series	Sample	Length
Tax invoice	Head office	HO/26-27/00001	HO/26-27/00001	14
Tax invoice	Shop 1	S1/26-27/00001	S1/26-27/00001	14
Tax invoice	Shop 2	S2/26-27/00001	S2/26-27/00001	14
Bill of supply	All	BS/26-27/0001	BS/26-27/0001	13
Credit note	All	CN/26-27/0001	CN/26-27/0001	13
Debit note	All	DN/26-27/0001	DN/26-27/0001	13
Delivery challan	All	DC/26-27/0001	DC/26-27/0001	13

Each series is unique within the GSTIN for FY 2026-27 because the prefixes differ. With five-digit counters, each shop can issue up to 99,999 invoices, comfortably above the 18,000 total. On 1 April 2027, every series switches to 27-28 and restarts at 1.

Can you run multiple series under one GSTIN?

Yes. Rule 46(b) explicitly allows "one or multiple series". Typical reasons:

• Separate counters or shops, so staff do not have to share a single counter in real time
• Different document types (tax invoice, bill of supply, export invoice)
• Online versus offline sales

The only condition is that no two documents under the same GSTIN carry the same number in the same financial year. Prefixes are the simplest guarantee.

Note that multiple registrations (different GSTINs, usually in different states) each run their own independent series. Uniqueness is tested per registration.

What should happen at the start of each financial year?

Rule 46(b) requires uniqueness "for a financial year". The GST portal advised taxpayers, from FY 2019-20 onwards, to start a new invoice series for each financial year. In practice:

1. Close the old series on 31 March.
2. Change the year code in every series on 1 April.
3. Restart counters at 1.
4. Make sure any invoice dated 31 March is not mistakenly numbered in the new series, and vice versa.

Software that resets series automatically on the financial-year boundary avoids the late-night 31 March scramble.

How are invoice series reported in GSTR-1?

Rule 48(3) requires the serial numbers of invoices issued during a tax period to be furnished in GSTR-1. In the return, the documents-issued table asks, for each document type, the series' starting and ending numbers, the total number issued and how many were cancelled.

That is why gaps matter: if your range for October is INV/26-27/00401 to INV/26-27/00500, the portal expects 100 documents issued, and any shortfall should appear as cancelled. A full walkthrough of the return is in GSTR-1 filing guide.

What about cancelled, voided and skipped numbers?

• Cancelled before supply: keep the number in the sequence, mark it cancelled, and count it in the cancelled column of GSTR-1.
• Printed in error: same treatment; never delete and reuse.
• E-invoice cancelled on the IRP: the IRN can be cancelled within the allowed window, but the invoice number cannot be reused for a new IRN. Issue the replacement with a new number. See cancel e-invoice.
• Software crash leaving a gap: document what happened and report the gap as cancelled.

Do e-invoices have extra numbering checks?

Yes. When you report an invoice to the IRP, the document number is validated against the permitted pattern and against duplicates. A number already used for an IRN under your GSTIN for that financial year is rejected as a duplicate. That makes discipline in your series even more important if you are an e-invoice taxpayer.

Which other GST documents need their own numbering?

Tax invoices are only one of the documents GST asks you to number. Section 31(3) lists several others, and each needs a serial number that follows the same discipline. A full set for a typical trader looks like this:

Document	When it is issued	Suggested prefix
Tax invoice	Taxable supplies	INV
Bill of supply	Exempt supplies or composition dealers	BS
Export invoice	Exports and SEZ supplies	EXP
Receipt voucher	Advance received before supply (Section 31(3)(d))	RV
Refund voucher	Advance refunded when no supply follows (Section 31(3)(e))	RF
Self-invoice	Purchases from unregistered suppliers taxed under reverse charge (Section 31(3)(f))	SI
Payment voucher	Payment to a supplier under reverse charge (Section 31(3)(g))	PV
Credit note / debit note	Corrections under Section 34	CN / DN
Delivery challan	Movement of goods without an invoice (Rule 55)	DC

Keeping these apart has a practical payoff. The documents-issued table in GSTR-1 asks for each document type separately, so a clean prefix per type turns that table into a copy-and-paste job instead of a manual count. It also helps when a tax officer asks for "all self-invoices for the year": you can pull one series rather than filter a mixed one. Receipt vouchers for advances are explained in advance payment under GST.

How should online stores and POS counters number invoices?

Shops that sell both at a counter and online often run into clashes because two systems generate numbers independently. Three rules keep you safe:

1. Give every system its own prefix. For example, POS invoices as P1/26-27/000001 and website orders as WB/26-27/000001. Both are 16 characters or fewer and cannot collide.
2. Do not let a marketplace number become your invoice number unless it fits Rule 46(b). Marketplace order IDs are often longer than 16 characters or contain characters such as underscores. Map each order to your own invoice number and keep the order ID in a reference field.
3. Check offline mode. POS systems that keep billing during an internet outage must not reuse numbers when they sync. Test this before peak season, not after.

If you issue a consolidated tax invoice at the end of the day for small B2C sales under ₹200 (as Rule 46 allows when the buyer is unregistered and does not want an invoice), that daily invoice also takes a number from a series, so plan a prefix such as DCN for it.

Common mistakes

• Prefixes that push numbers past 16 characters, such as full branch names or four-digit years twice.
• Using #, spaces, dots or underscores.
• Two counters under one GSTIN starting from the same number with the same prefix.
• Reusing a cancelled number for the next sale.
• Forgetting to change the year code on 1 April, so numbers clash with last year's series.
• Numbering credit notes inside the invoice series, which confuses GSTR-1 reporting.
• Manual invoice books at a second counter without a distinct prefix.

Key takeaways

• Max 16 characters; only letters, numbers, hyphen and slash.
• One or many series are allowed, but each number must be unique within the financial year for a GSTIN.
• Use prefix + year code + counter, such as INV/26-27/00001.
• Restart every series on 1 April.
• Never reuse cancelled numbers; report them in GSTR-1.

Billing Software by Betterwork lets you set separate series per branch and document type, checks the 16-character limit, and switches the year code on 1 April automatically. If you want to see it with your own series, you can book a demo.

This guide is general information, not tax advice. Rules last checked on 20 October 2026; confirm with your tax professional for your situation.