GST resources
GST Invoice Numbering Rules
Rule 46 of the CGST Rules says exactly how a tax invoice must be numbered. The rule is short, but breaking it shows up in your GSTR-1 and, for larger businesses, gets an e-invoice rejected.
The rule
- A consecutive serial number, in one or more series
- No more than 16 characters
- Only letters, numbers, the hyphen (-) and the slash (/)
- Unique for a financial year: the same number cannot be used twice in a year
- Credit notes and debit notes follow the same pattern in their own series
Series you can keep
You can run several series at once, as long as each is consecutive and the combination is unique: one per branch, one per counter, or one for each document type. Many businesses put the financial year in the prefix so numbering restarts on 1 April without clashing with last year. Every series is listed in the "documents issued" table of GSTR-1 with its first and last number and the count of cancelled documents.
Worked example
| Use | Series | Characters |
|---|---|---|
| Main counter invoices | SLS/26-27/0001 | 14 |
| Second counter | SLS2/26-27/0001 | 15 |
| Credit notes | CN/26-27/0001 | 13 |
| Too long (rejected) | SriLakshmiStores/26-27/0001 | 27 |
Sample series for Sri Lakshmi Stores, a kirana in Mysuru.
Reporting the series
In April 2026, the main counter issued SLS/26-27/0001 to SLS/26-27/1450 and cancelled three. GSTR-1 table 13 shows that range with 1,450 total and 3 cancelled, so 1,447 net. The cancelled numbers stay on record marked cancelled; they are not reused or deleted.
When to issue the invoice
| Supply | Time limit |
|---|---|
| Goods, when they are moved | Before or at the time of removal |
| Goods, other cases | Before or at the time of delivery or making them available |
| Services | Within 30 days of supply |
| Services by banks, NBFCs and insurers | Within 45 days of supply |
| Continuous supply of goods | On or before the date of the account statement or payment |
Common mistakes
- Numbers that restart every month, creating duplicates within the year
- Prefixes with spaces, dots or underscores
- Gaps from deleted invoices instead of cancelled ones
- Handwritten bill books running alongside software with an overlapping series
- Reusing last year's numbers without a year in the prefix
Moving from a bill book to software
If you switch from printed bill books to billing software mid-year, close the bill book series on the last day you use it and start the software on a new prefix, rather than continuing the same numbers. Both series are then reported in the documents issued table of GSTR-1, and nobody can confuse a handwritten SLS/0145 with a printed one.
Do not keep two systems running for the same counter. A second series for the same sales is allowed in law, but in practice it is where missing and duplicate invoices come from.
Credit notes, debit notes and other documents
Credit notes and debit notes need their own consecutive serial numbers of up to 16 characters, and must refer to the original invoice. Receipt vouchers for advances, refund vouchers and delivery challans are also numbered and reported in the documents issued table. A separate prefix for each document type, such as CN/, DN/ and DC/, keeps them apart.
Numbering on e-invoices
Businesses above the ₹5 crore e-invoicing threshold must report each B2B invoice to the Invoice Registration Portal. The portal rejects a document number that has already been used for the same type of document in the same financial year, so a duplicate is caught at once. The same 16-character rule applies to the document number sent to the portal.
How TripleBill helps
TripleBill numbers invoices, credit notes and other documents in sequence with your chosen prefix, never reuses a number, keeps cancelled documents with their number, and lists the series in the GSTR-1 documents summary.
This page is general information about GST in India, not tax advice. Rates, thresholds and rules change; confirm with the GST portal or a chartered accountant before acting.
Last reviewed and sources
Last reviewed: November 2026. Facts on this page were checked against:
- CGST Act, 2017, section 31
- CGST Rules, 2017, rules 46(b), 47 and 53
- FORM GSTR-1, table 13 (documents issued)
Frequently asked questions
How many characters can a GST invoice number have?
Up to 16.
Which characters are allowed?
Letters, numbers, the hyphen and the slash.
Can I have different series for different branches?
Yes. Each series must be consecutive and numbers must not repeat within the financial year.
Should numbering restart every financial year?
It may. Numbers only need to be unique within a financial year, so most businesses start a new series each April, often with the year in the prefix.
What do I do with a cancelled invoice?
Keep the number marked as cancelled and report it in the documents issued table. Do not reuse it.
Is the number case-sensitive?
Treat it as case-insensitive. Do not use "inv/1" and "INV/1" as two different invoices.
Does a cash memo need a serial number?
A tax invoice or bill of supply does. Use one consecutive series for counter bills.
Can two branches use the same number?
Not under the same GSTIN in the same year. Give each branch its own prefix, such as SLS1/ and SLS2/, so numbers never collide.
What if my software skipped a number?
Report the gap honestly: if the number was never issued, note it with your accountant; if an invoice was cancelled, keep it marked cancelled. Do not create a backdated invoice to fill the gap.
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