Invoice numbering looks like an admin detail until an officer asks why invoice 214 is missing, or why two invoices in the same year carry the same number. Rule 46 of the CGST Rules sets out what a tax invoice must contain, and its numbering rule is short enough to learn once and get right forever.
What Rule 46 actually asks for
Every tax invoice needs a consecutive serial number that:
- is not longer than 16 characters;
- uses only letters, numbers, the hyphen
-and the slash/; - runs in one or more series — you may keep several;
- is unique for the financial year.
That last point is the one people trip over. A number can repeat across years (INV-001 in 2025-26 and again in 2026-27), but never twice inside the same April-to-March year. Most businesses avoid the question entirely by putting the year into the prefix.
| Example | Characters | Fine? |
|---|---|---|
INV/26-27/0001 | 14 | Yes |
BLR-INV-26-27-0001 | 18 | No — too long |
INV#0001 | 8 | No — # is not allowed |
0001 | 4 | Yes, but only if 0001 is never reused within the year |
When to keep more than one series
Separate series are allowed and often sensible:
- One per document type. Tax invoices, bills of supply, credit notes and debit notes each in their own series, so a credit note never sits between two invoices.
- One per branch or place of business. A Bengaluru counter and a Chennai counter can each run their own series without coordinating numbers, because different states mean different GSTINs. Within one GSTIN, give each series a distinct prefix.
- One per sales channel. Marketplace invoices and direct invoices kept apart makes reconciliation easier.
Each series must be consecutive, and the complete number must be unique across all your series for the year — so use a distinct prefix per series.
Gaps, cancellations and GSTR-1 Table 13
"Consecutive" does not mean nothing may ever be cancelled. It means every number is accounted for. GSTR-1 asks for a summary of documents issued in each series — the first and last number, the total, and how many were cancelled. A cancelled invoice keeps its number; it is reported as cancelled rather than reused or skipped.
A gap you cannot explain is worse than a cancellation you reported. Never delete an issued invoice to "free up" its number.
The start of a new financial year
On 1 April, start each series afresh — or carry on, if your numbers already include the year. Either works; what matters is that no number from the previous year is issued again in the new one.
How Books by finzko handles it
In Books by finzko, each numbering series carries its own prefix, its own counter per financial year, and the document title it prints (Tax Invoice, Bill of Supply and so on). Branches can have their own series, cancelled numbers are recorded rather than reused, and the series summary feeds GSTR-1 Table 13 directly. Keep the prefix short enough that the full number stays within 16 characters.
This article explains Rule 46 in general terms. Check the current text of the CGST Rules, and any notifications that apply to your business, before relying on it.