Invoice Numbering Rules Under GST (With Format Examples)

Invoice numbers look like a small detail, but under GST they are a compliance requirement. Here are the rules in plain language and some formats that work well.

The rules

• Consecutive serial number: numbers must run in sequence, with no gaps or repeats within a financial year.
• Maximum 16 characters.
• Allowed characters: letters, numbers, a hyphen (-) and a slash (/). Avoid other symbols and spaces.
• Unique for the financial year (1 April to 31 March). You can restart from 1 each April.
• You may use separate series for different branches, locations or document types, as long as each series stays sequential and unique.

Good formats

Keep it short enough to fit even when the serial grows. If you use a year code, remember the limit of 16 characters.

Common mistakes

• Deleting an invoice and skipping the number. Cancel it and keep the record instead. Mention it as cancelled.
• Using the same number twice in different months.
• Mixing quotation and invoice numbers. Keep a separate series for each document type. Our tools use QT-, INV-, PI-, PO-, DC- and RC- prefixes so you can keep them apart.
• Editing an issued invoice. Use a credit note or debit note for corrections.

Numbering other documents

Delivery challans also need consecutive serial numbers of up to 16 characters. See delivery challan rules. Proforma invoices and quotations are not tax invoices, but a clear series helps tracking. Read quotation vs invoice vs proforma.

Create numbered documents quickly with the invoice generator. It remembers your last number in your browser. See also GST invoice format.