Invoice numbering rules under GST

What the rule actually says

Rule 46 of the CGST Rules asks for a consecutive serial number, in one or multiple series, containing alphabets, numerals, the hyphen or dash (-) and the slash (/), not exceeding 16 characters, and unique for a financial year. The same rule applies to bills of supply, credit and debit notes, receipt vouchers and delivery challans.

Four points follow from that:

• Length: count every character, including slashes. 16 is the maximum.
• Characters: no spaces, underscores, hashes or brackets.
• Consecutive: numbers run in order within a series; gaps need an explanation, such as a cancelled invoice.
• Unique per financial year: the same number cannot appear twice between 1 April and 31 March. Starting again from 0001 in a new year is allowed.

This is general information, not tax advice.

Sample formats and their length

Putting the financial year in the number is not required, but it makes the number unique across years at a glance and helps when a buyer quotes an old bill.

When to use more than one series

Multiple series are allowed and often sensible:

• By branch or godown: JPR/ for Jaipur, AJM/ for Ajmer, so each counter numbers its own bills without clashing.
• By document: INV/ for tax invoices, BOS/ for bills of supply, CN/ for credit notes, DC/ for delivery challans.
• By channel: a separate series for counter sales and for field orders.

Every series you use is reported in the documents-issued table of GSTR-1 with its from and to numbers, the total issued and the number cancelled. Too many series make that table tedious, so keep it to what you need. More on that in what is GSTR-1.

Extra care if you issue e-invoices

If your business is under e-invoicing, the Invoice Registration Portal rejects a document number already used by your GSTIN in the same financial year, even if the earlier IRN was cancelled. Its validation also does not accept numbers starting with 0, a slash or a hyphen, so begin your series with a letter or a non-zero digit. Cancelling and reissuing under the same number is therefore not possible; you issue a fresh number. See e-invoicing and IRN and confirm current validations on the e-invoice portal.

Gaps, cancellations and year change

Cancelled numbers

Do not reuse a cancelled number. Keep the cancelled invoice (all copies, marked cancelled) and report it in the cancelled count in GSTR-1.

Missing numbers

A jump from 0412 to 0415 with no record of 0413 and 0414 invites questions during audit or scrutiny. Find out why: a software glitch, a voided draft or a book left at another counter.

1 April

Reset the series or change the year part of the prefix. If you leave a number like INV/0001 running across years without a year marker, you must not restart it, or you will have two INV/0001 bills in different years that are hard to tell apart.

A quick numbering checklist

1. Decide the series before 1 April and write them down.
2. Count the characters of the longest number you will reach, not the first one. INV/25-26/9999 is 14; INV/25-26/10000 is 15.
3. Use leading zeros so numbers sort correctly.
4. Give each counter or salesperson their own series instead of sharing one paper book.
5. Check the documents-issued summary every month before filing.

Doing this with Tally and Cashflow OS

In TallyPrime, each voucher type has its own numbering method, prefix and suffix, and you can set numbering to restart from a date such as 1 April. When a salesperson creates a sales voucher from Cashflow OS, the entry goes into Tally through the connector, so it follows the numbering you have set there; you do not maintain a second series in the app. Quotations, proformas, purchase orders and challans made as documents in Cashflow OS carry their own numbers separate from your tax invoices.