Nobody sets up numbering on day one. They raise the first invoice, notice it says INV-1, decide that looks unserious, change it, and by month four there are three prefixes in play and a CA asking why INV/41 follows INV/38.
What GST asks for
- Consecutive
- A serial number that does not jump
- Unique
- Within the financial year
- At most
- Sixteen characters
- Allowed
- Letters, numerals, hyphens, slashes — and more than one series, if each is consecutive
Why gaps matter more than format
The format is largely yours to choose. What is not negotiable is that the series runs without holes. A missing number invites the obvious question — was there an invoice there, and where did it go? — and answering it a year later means reconstructing what happened from memory.
This is why a deleted draft releases its number back for the next document to use. It looks like a small behaviour and it is the difference between a clean series and one with explaining to do.
Step by step
Settings → Numbering
One row per document type. Invoices, quotations, sales orders, credit notes, purchase orders, bills, delivery challans — each with its own series.
Set the prefix
Short and obvious. INV, QT, PO, CN. Remember the sixteen-character ceiling: a long prefix plus a financial year plus four digits gets there faster than you expect.
Add the financial year
INV/2026-27/0001. The count restarts each April, which is what auditors expect and what makes “unique within the financial year” true by construction rather than by care.
Padding, and the next number
Four digits is standard. If you are moving mid-year from another system, set the next number to carry on from where that one stopped — do not restart at 1, or you will have two documents with the same number in one year.
Set the ones you have not used yet
This is the step people skip. A series heals itself on first use — but not before, so the first credit note or delivery challan you ever raise carries whatever the default was, permanently.
The bit that trips people up. Numbering configures itself the first time you raise that kind of document, and not a moment earlier. Set every series on day one; it takes ten minutes and it is the only time you can do it without leaving a document behind with the wrong number on it.
More than one series
Billing from two branches, or keeping export invoices apart from domestic ones? More than one series is allowed, provided each is consecutive within itself. Set a per-branch series and each branch counts independently — INV/DEL/2026-27/0001 and INV/BLR/2026-27/0001 living side by side, both clean.
Common questions
What does GST actually require of an invoice number?
A consecutive serial number, unique for the financial year, no more than sixteen characters, using letters, numerals, hyphens or slashes. More than one series is allowed as long as each is consecutive.
Can I have a separate series per branch?
Yes, provided each series is consecutive within itself.
What happens to the number if I delete a draft?
It is released and reused by the next document, so the series stays consecutive.
Can I change the prefix mid-year?
You can, but treat it as starting a new series rather than renaming the old one — what is not wanted is a single series that jumps.
Correct as of September 2026. Invoice content rules sit in Rule 46 of the CGST Rules; check the current text before relying on this for a filing.
Next
See it with your own data
Start free, import a spreadsheet of your customers, and raise a real GST invoice in the first ten minutes. No card, no sales call.