Invoice number check
Rule 46(b) of the CGST Rules puts two hard limits on an invoice number: at most 16 characters, and letters and numerals with only a hyphen or slash besides. Break either and the GSTR-1 upload rejects the record. Check yours below — it runs in your browser and nothing is sent anywhere.
What Rule 46(b) actually requires
The rule asks for four things at once, and only two of them can be seen in a single number. It must be a consecutive serial number, it must be unique within the financial year, it must not exceed sixteen characters, and it may contain only alphanumerics, hyphen and slash.
Length and character set are visible in the number itself, which is what the checker above tests. Consecutiveness and uniqueness are properties of the whole series — they need the register, not one row, which is what the batch check is for.
Why sixteen characters catches people out
Almost nobody sets out to write a seventeen-character invoice number. It happens because the number is assembled from parts: a branch code, a financial year, a document type and a running sequence. Each is reasonable on its own and the concatenation quietly runs over.
INVOICE/MUMBAI/2026-27/00412 is twenty-eight characters and will be rejected. MUM/26-27/00412 is fifteen, carries the same information, and will not. The usual fix is shortening the branch token and the year rather than touching the sequence.
The one that is invisible
A leading or trailing space. It survives a copy-paste out of a spreadsheet, it looks like nothing on screen, and it makes the number fail the character-set test on upload. If a number looks correct and is still rejected, this is the first thing to check — the checker above flags it explicitly for that reason.
Common questions
What is the maximum length of a GST invoice number?
Sixteen characters. Rule 46(b) of the CGST Rules 2017 requires a consecutive serial number not exceeding sixteen characters. A longer number is rejected by the GSTR-1 upload with error RET191115.
Which characters are allowed in an invoice number?
Letters, numerals, hyphen and slash. Rule 46(b) permits alphanumerics with those two special characters and nothing else — no spaces, hashes, ampersands, dots or brackets.
Can I restart my invoice numbering each financial year?
Yes, and it is the normal practice. Rule 46(b) requires the series to be unique within a financial year, so starting again at 1 on 1 April is correct. What is not permitted is two invoices carrying the same number inside the same year.
Can I run more than one invoice series at the same time?
Yes. Separate series per branch, per place of business or per document type are allowed, provided each series is consecutive in itself and every number stays unique within the financial year across all of them.
What is error RET191115?
The GSTR-1 upload error returned when an invoice number breaches Rule 46(b) — most often because it exceeds sixteen characters. The record is rejected and the return has to be corrected and resubmitted.
The number is one of sixteen checks
Tax head against place of supply, HSN length against your turnover band, the arithmetic line by line, rounding at invoice level — an invoice fails on any of them. Running the whole thing takes about as long as this did.
General information about Indian GST, not tax advice. Rule 46 is amended by notification from time to time — confirm the current position with your CA before relying on it. See also error RET191115.