Under GST, every tax invoice needs a consecutive serial number of not more than 16 characters, unique for the financial year, using letters, numbers, hyphens or slashes, in one or more series. That rule comes from the invoice provisions of the CGST Rules (Rule 46). For an exporter, a clean numbering system matters twice over: the same invoice number appears on your GST return, your export invoice, the client's payment reference and a row in Part 2B of your monthly EDF.
Key takeaways
- Maximum 16 characters, including separators like "/" and "-".
- Numbers must be consecutive within a series and must not repeat within a financial year.
- You can run several series — for example, one for exports and one for domestic invoices.
- Never reuse a cancelled number; cancel it, record why and move on.
- Pick a format before 1 April and stick to it for the whole year.
The rule in plain words
The GST invoice rules ask for a serial number that is:
| Requirement | What it means in practice |
|---|---|
| Up to 16 characters | "EXP/26-27/0041" (14) is fine; "EXPORT-INV/2026-27/00041" (24) is not |
| Consecutive | 0041 follows 0040; no jumps without a recorded reason |
| Unique for the financial year | No two invoices in FY 2026-27 carry the same number in the same series |
| Letters, numbers, "-" and "/" allowed | Avoid spaces, underscores and other symbols |
| One or more series | Separate series per business vertical, branch or type are fine |
This is a commonly misunderstood area, so ask your CA to confirm how it applies to your setup, especially if you are on e-invoicing.
Designing a numbering scheme that works for exports
A good invoice number does three jobs: it satisfies GST, it's easy for a foreign client to quote, and it tells you at a glance what kind of invoice it is.
Here is the scheme Asha Design Studio, a fictional Jaipur design firm with both Indian and overseas clients, adopted for FY 2026-27:
| Series | Format | Example | Length | Used for |
|---|---|---|---|---|
| Export | ADS/E/26-27/001 | ADS/E/26-27/014 | 15 | All foreign-client invoices under LUT |
| Domestic | ADS/D/26-27/001 | ADS/D/26-27/087 | 15 | Indian clients, GST charged |
| Credit notes | ADS/CN/26-27/01 | ADS/CN/26-27/03 | 15 | Adjustments to any invoice |
Why this works:
- The "E" makes export invoices instantly recognisable when Asha prepares the monthly EDF. She filters the register by "E" and every Part 2B row is right there.
- The financial-year segment resets uniqueness each April without confusion.
- Three-digit counters leave room for 999 invoices per series, which is plenty for a small studio. A busier firm would use four digits and shorten the prefix.
Why a separate export series helps with the EDF
Since 1 October 2026, every invoice to a foreign client goes into a monthly EDF, one row per invoice in Part 2B. Your bank enters those invoice numbers into EDPMS and later matches payments against them.
A separate export series gives you:
- A clean EDF list. In October 2026, Asha raised ADS/E/26-27/011 to ADS/E/26-27/014. The October EDF has exactly four rows, in order. Any gap would jump out.
- Easier matching. Clients quote "ADS/E/26-27/012" in their payment reference and your bank's matching team can find it immediately.
- Simpler GST reconciliation. Export invoices under LUT are reported differently from domestic taxable invoices. One series per type makes the return easier to prepare.
You can still run a single series for everything — the GST rules allow it. It just makes the monthly EDF a filtering exercise rather than a copy.
Handling cancelled, revised and split invoices
This is where clean numbering usually breaks.
Cancelled invoice. Don't reuse the number. Mark it cancelled in your register with a reason and keep a copy. If it was already listed on an EDF, tell your bank — our guide to a cancelled invoice after EDF submission covers the steps.
Revised amount. If the client disputes part of an invoice after it was issued, the usual route is a credit note rather than reissuing a new invoice with the same number. Our credit note generator has its own numbering field.
Invoice split across months. If a project is billed in milestones, each milestone gets its own number in sequence. Don't use suffixes like "014A" and "014B" unless your CA is comfortable with them; a fresh number is cleaner.
Proforma invoices. A proforma isn't a tax invoice. Number proformas in their own series (for example "ADS/PF/26-27/01") so they never break the tax-invoice sequence.
Common numbering mistakes
| Mistake | Why it causes trouble | Fix |
|---|---|---|
| Restarting at 001 mid-year after changing software | Duplicate numbers in the same FY | Carry the counter forward, or start a new clearly named series |
| Numbers longer than 16 characters | Non-compliant; may be rejected by e-invoicing systems | Shorten the prefix |
| Using dates as numbers ("20261014") | Two invoices on one day collide | Use a counter |
| Gaps with no explanation | Looks like missing invoices | Keep a register noting cancelled numbers |
| Reusing last year's numbers without a year segment | Confusion across years in EDPMS and GST | Include "26-27" or similar |
This article is general information, not legal or tax advice.
A short setup checklist for April
Before the new financial year starts:
- Decide your series and formats, and write them down in one line each.
- Check every format is 16 characters or fewer at the maximum counter.
- Configure your accounting software or invoice tool to start each series at 001.
- Make sure your LUT for the new year is filed before the first export invoice.
- Tell your team which series to use for which client.
If you use our free GST invoice generator or export invoice generator, you set the invoice number yourself, so keep your register alongside and fill the next number in sequence.
Frequently asked questions
How many characters can a GST invoice number have?
A GST invoice serial number can have up to 16 characters. Letters, numbers, hyphens and slashes count towards the limit. Check your longest possible number — at the highest counter — against the limit before you adopt a format.
Can I use different invoice series for export and domestic invoices?
Yes. The GST rules allow one or more series, as long as each is consecutive and unique within the financial year. Many exporters keep a separate export series because it makes the monthly EDF and GST reporting easier.
Do invoice numbers have to restart every financial year?
They must be unique within a financial year. Most businesses include the year in the number (for example "26-27") and restart the counter each April. Confirm your approach with your CA if your software handles it differently.
What do I do with an invoice number I cancelled?
Don't reuse it. Record the cancellation and the reason in your invoice register and keep the cancelled document. If the invoice was already listed on an EDF, inform your bank so its EDPMS record can be corrected.
Does the EDF require a particular invoice number format?
No. The EDF simply asks for the invoice number and date in each Part 2B row. Use exactly the number printed on the invoice so your bank can match the payment later.
Bottom line
Keep invoice numbers short, sequential and separate by type, and the GST return, the client's payment reference and your EDF all line up without effort. Start the next invoice in our free export invoice generator, then drop it straight into a Part 2B row in the EDF form generator.
This guide is general information for Indian businesses, not legal or tax advice. Rules and bank processes change — confirm specifics with your AD bank or chartered accountant.