16
Maximum length
Keep the full invoice number within 16 characters, including the prefix and separators.
Core checklist
Main information to capture on a tax invoice.
Rule 46 requirements and transaction-specific conditions can vary. At a practical level, businesses should prepare the following details and confirm special cases with a CA.
- Supplier name, address and GSTIN
- Consecutive invoice number
- Date of issue
- Recipient name and address
- Recipient GSTIN/UIN when registered
- HSN code for goods or SAC for services
- Description and quantity where applicable
- Taxable value after discount
- GST rate and tax amount
- Place of supply for inter-state supply
- Reverse-charge indication when applicable
- Authorised signature or digital authentication as required
Numbering check: Keep invoice numbers unique and sequential within the financial-year series. Avoid changing or reusing a number after the invoice has been issued.
GST invoice number format
Maximum 16 characters, unique for the financial year.
Rule 46 of the CGST Rules requires a consecutive serial number that does not exceed 16 characters. It may use alphabets, numerals, the hyphen or dash and slash, and can be maintained in one or multiple series as long as the number is unique for the financial year.
A/1
Allowed structure
Letters, numbers, hyphen/dash and slash can be combined. Example formats include INV/26-27/042 or N26/00421.
FY
Unique series
Use a consecutive series that stays unique within the financial year. Multiple series can be used where your process requires them.
Official reference: See CBIC invoice rules. For goods, Rule 48 also describes original, duplicate and triplicate copies; e-invoice rules can change how those copy requirements apply.
Tax split
When to show CGST/SGST and when to show IGST.
IN
Intra-state supply
When supplier location and place of supply are in the same state, the GST rate is normally split into CGST and SGST/UTGST.
OUT
Inter-state supply
When the place of supply is in another state, the invoice normally shows IGST instead of separate CGST and SGST.
POS
Place of supply
This is not always the customer's billing address. Service and special-transaction rules can differ, so verify uncertain cases.
Common mistakes
Checks to perform before sending the PDF.
- Wrong customer GSTIN or state
- Duplicate invoice number
- HSN/SAC omitted where required
- Tax-inclusive rate treated as tax-exclusive
- IGST used for an intra-state transaction
- Incorrect invoice or due date
- Taxable value not matching line totals
- Missing supplier contact or payment details
GST invoice format questions
Is a GST invoice number required to be sequential?
Yes. The invoice number should follow a consecutive series and remain unique for the financial year. Billorex generates increasing numbers using your chosen prefix.
What is the maximum length of a GST invoice number?
Under Rule 46, the serial number must not exceed 16 characters. Alphabets, numerals, hyphen/dash and slash may be used in the series.
Are invoices for goods prepared in triplicate?
Rule 48 describes original, duplicate and triplicate copies for goods invoices. Where the e-invoice provisions of Rule 48(4) apply, the normal copy provisions in sub-rules (1) and (2) do not apply in the same way, so check the current e-invoice requirements for your business.
What is the difference between HSN and SAC?
HSN classifies goods, while SAC classifies services. Use the code that applies to the item or service supplied.
Can I use a PDF invoice?
Businesses commonly issue invoices electronically as PDFs. The required invoice particulars still need to be present, and e-invoicing rules may add IRN or QR requirements for notified taxpayers.
Does Billorex generate an IRN?
No. Billorex can prepare e-invoice JSON and store returned IRN/QR details. IRN generation and submission require an authorised IRP or GSP; Billorex does not submit directly to the IRP.
Let the invoice form do the arithmetic.
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