Invoiceo

Free tool · India

Invoice number format checker and generator

A GST invoice number has to be short, tidy and never repeat. Check one you already use, or lay out a scheme with the financial year in it and see the first numbers before you commit.

Check a number

Up to 16 characters: letters, digits, “-” and “/”.

Plan a numbering scheme

  • INV/26-27/000114 characters
  • INV/26-27/000214 characters
  • INV/26-27/000314 characters
  • INV/26-27/000414 characters
  • INV/26-27/000514 characters

This style fits. A prefix of up to 5 characters would still fit.

The rule in one list

  • At most 16 characters.
  • Letters, digits, hyphen and slash only.
  • Consecutive and never repeated within the financial year.

Questions people ask

What is the GST rule for invoice numbers?

Under Rule 46 of the CGST Rules, an invoice carries a consecutive serial number of not more than sixteen characters, in one or more series, containing only letters, numbers, a hyphen and a slash, and unique for the financial year. Check the current rule on the CBIC site.

Can I use spaces or other symbols?

No. Only letters, digits, '-' and '/' are allowed. A space, an underscore, a dot or a hash sign makes the number invalid for a GST invoice.

Must the numbers be strictly in order?

They must be consecutive within a series, with no repeats. Skipping numbers without a reason invites questions, so if an invoice is cancelled, keep its number and mark it cancelled rather than reusing it.

Do I have to restart at the new financial year?

The number must be unique within a financial year, and putting the year in the number (INV/26-27/0001) makes that easy: the serial restarts at 0001 each April while the full number stays unique.

Does this apply outside India?

The 16-character limit is a GST rule. Other countries have their own, usually lighter, rules: a unique, sequential number is the common thread. The tool is built for the GST rule.

Checked against the official sources

Last reviewed on 11 October 2026. Tax rules and limits change, and we cannot see your whole situation, so treat this page as a guide, not advice. If something here looks out of date, the official pages below are the ones to trust, and we would be grateful if you told us.

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