FY 2026-27 started on 1st April, and if your invoice number still reads something like "INV/2025-26/0847," you have a problem. The GST portal expects a fresh series for the new year. Miss this and you're looking at GSTR-1 mismatches, rejected e-invoices, and buyers who suddenly can't claim ITC on your bills.
This isn't a new rule. It's been in the CGST Rules since 2017. But every April, thousands of small businesses forget to reset, and every April, the same complaints show up on the GST helpdesk. Here's what the rule actually says and how to fix your numbering before it costs you a client.
What is Rule 46(b) of CGST Rules?
Rule 46(b) of the CGST Rules, 2017 says every tax invoice needs a consecutive serial number, capped at 16 characters, made up of letters, numbers, hyphens, and slashes. That number has to be unique for a financial year.
Here's the part most guides skip: the rule doesn't technically force you to restart at 1 every April. It only says the number can't repeat within the same year. Practically speaking, though, almost every business, and every accounting software including Tally, resets to 001 with a new financial-year prefix. It's cleaner for reconciliation, and it's what GSTN's own advisory recommended back in 2019. So while a strict legal reading gives you some flexibility, the safe and standard approach is: new year, new series.
Key Rules for GST Invoice Numbering in FY 2026-27
Before you touch your billing software, lock these three points in:
• Maximum 16 characters. Your entire invoice number, prefix, year, serial, everything, has to fit within that limit.
• Unique and sequential. No gaps, no repeats. If invoice 47 is followed by invoice 49, an officer will ask where 48 went.
• Allowed characters only. Letters (A-Z), numbers (0-9), hyphen (-), and slash (/). Nothing else. No dots, no spaces, no special symbols.
Case-insensitivity is worth knowing too: since mid-2025, the e-invoice portal treats "abc101" and "ABC101" as identical and auto-converts everything to uppercase before generating the IRN. So pick a case convention and stick to it.
Best Invoice Formats for FY 2026-27 (Examples)
You don't need anything fancy. A clear prefix, the financial year, and a sequential number covers it.
Example 1 (Standard): INV/2026-27/001
Example 2 (Branch-wise): DEL/26-27/001
|
Format Type
|
Example
|
Best For
|
|
Standard series
|
INV/2026-27/001
|
Single-location businesses, freelancers
|
|
Branch-wise series
|
DEL/26-27/001, MUM/26-27/001
|
Multi-branch traders, distributors
|
|
Document-type split
|
INV vs CN vs DN prefix
|
Businesses issuing frequent credit/debit notes
|
|
Numeric only
|
26270001
|
ERP systems needing pure numeric sorting
|
Whichever format you pick, keep it under 16 characters and don't mix conventions across invoices raised from the same GSTIN.
Why You Shouldn't Continue the FY 2025-26 Series
Carrying your old series into the new year isn't just untidy bookkeeping. It creates three real problems.
Reconciliation issues in GSTR-1. The portal expects your outward supply data to line up with a financial-year-specific series. Continuing last year's numbers makes matching purchase and sales registers harder, both for you and for the department during scrutiny.
Rejection in e-Invoicing (IRN generation fails). If your turnover crosses ₹5 crore, e-invoicing is mandatory from FY 2026-27. The IRP tracks document series by GSTIN and financial year. A number that doesn't reflect the year reset can trigger IRN generation errors, which means the invoice isn't legally valid until it's fixed.
Buyer's ITC gets blocked. This is the one that actually costs you clients. If your invoice numbering is inconsistent or duplicated, it can get flagged during reconciliation on the buyer's end, delaying or blocking their input tax credit. A buyer who loses ITC because of your invoice hygiene won't wait around to find out why.
A Jaipur Case Study
A textile trader in Jaipur's Johari Bazaar kept using his FY 2025-26 series, "JB/25-26/0412" and onward, straight into April 2026, just changing the date on each bill. By the third week of April, his accountant noticed something odd: two invoices, raised on different dates, had generated IRNs that conflicted in the e-invoice system because the year segment hadn't changed.
The result: 14 invoices worth roughly ₹9.6 lakh got stuck in "pending" status on the IRP. His largest buyer, a garment wholesaler in Chandpole, held back payment on three of those invoices until fresh, correctly numbered ones were issued. The fix took two days and one late-night call to his software vendor, a delay that was entirely avoidable with a five-minute settings change on 1st April.
“unique for a financial year” — Rule 46(b), CGST Rules, 2017
How to Update Invoice Series in TallyPrime / Accounting Software
If you're on TallyPrime, resetting your series takes a few minutes:
1. Go to Voucher Type. Gateway of Tally, then Create/Alter, then Voucher Type, and select "Sales" (or the relevant invoice type).
2. Turn on Automatic Numbering. Set "Method of Voucher Numbering" to Automatic, and make sure "Prevent Duplicates" is enabled.
3. Add Prefix/Suffix. Under "Set Starting Number," add your FY prefix, for example, prefix "INV/26-27/" with starting number 1.
4. Restart the numbering. Confirm the starting number resets to 1 (or continues from your last FY 2025-26 count, whichever format you're using) and save.
5. Test with a dummy invoice. Raise one test voucher and check the number generated correctly before you start billing for real.
For businesses using other software, Zoho Books, Vyapar, or a custom ERP, the steps are nearly identical: find the voucher/document numbering settings, update the prefix to reflect 26-27, and confirm the starting serial before your first real invoice goes out.
Related Guides
• GST Registration Amendments: What Changed in FY 2026-27
• GSTR-1 Filing Checklist for Small Businesses
• How to Fix IRN Generation Errors on the E-Invoice Portal
Conclusion
Resetting your invoice series isn't complicated, but skipping it is expensive. One five-minute settings change on 1st April saves you from GSTR-1 mismatches, rejected e-invoices, and buyers who lose patience waiting for a corrected bill. If you haven't reset yet, do it before your next invoice goes out, not after your first IRN rejection.
Get Help with GST Filing
Struggling with GST compliance or filing? Our GST Filing Services can help you stay on top of invoicing, returns, and reconciliation without the last-minute scramble.
Frequently Asked Questions
How do I reset invoice numbers in Tally for the new financial year?
Go to Voucher Type, alter your Sales voucher, set Method of Numbering to Automatic, then update the Starting Number and prefix under "Set Starting Number" to reflect FY 2026-27, and save.
What is the GST invoice format for FY 2026-27?
Any format works as long as it's within 16 characters, uses only letters, numbers, hyphens, and slashes, and stays unique within the year. A common format is INV/2026-27/001.
What is the maximum number of characters allowed in a GST invoice number?
16 characters, including the prefix, year, and serial number, as per Rule 46(b) of the CGST Rules, 2017.
Is it mandatory to restart invoice numbers from 1 every financial year?
No. Rule 46(b) only requires the number to be unique within a financial year, not that it restarts at 1. Most businesses reset to 1 anyway because it's simpler to track and matches how accounting software is configured by default.
What happens if I use the old invoice series in FY 2026-27?
You risk GSTR-1 reconciliation mismatches, e-invoice IRN generation failures if you're above the e-invoicing threshold, and delayed or blocked ITC for your buyers.