Financial year invoice numbering: why April–March breaks your ERP

Here's a subtle thing that gets most imported ERPs and SaaS tools in trouble the moment an Indian customer files their first GSTR-1:

Invoice numbers in India must sequence within the financial year (01 April — 31 March), not the calendar year. The sequence resets on 1 April. If you run on a Jan–Dec calendar, GSTR-1 will flag mismatches and your CA will spend a weekend un-doing the damage.

What CGST Rule 46 actually says

Rule 46 of the CGST Rules mandates that every tax invoice carry a consecutive serial number, unique for a financial year. The format is at your discretion — alphanumeric, prefixed, dashed, anything — but it must be:

1. Unique within the financial year.
2. Strictly consecutive (no gaps).
3. No more than 16 characters.

That's it. Three rules. Most teams get one wrong.

The common mistakes

Mistake 1: Calendar year reset

If your SaaS numbers invoices as INV-2026-0001 and resets at the start of the calendar year, it will reset on 1 January. You'll issue INV-2026-0001 on 1 Jan — but your FY 25–26 still has three months left, and you already issued INV-2025-9834 in December. Now on your 1 January invoice, you have a number that's lower than December's. GSTR-1 flags it.

Mistake 2: Gaps

If an invoice is deleted (not cancelled — actually deleted from the record), the sequence has a gap. Gaps are not legal under Rule 46. You must cancel, not delete, and even a cancelled invoice keeps its number in the ledger.

Mistake 3: > 16 characters

BLUEPRINT-FY2025-2026-0001 is 25 characters. It won't pass GSTN validation. Use something short: BP/26/0001 is 10 characters and still unambiguous.

A scheme that works

{prefix}/{FY}/{sequence} where FY is the starting calendar year of the financial year (so FY 2025–26 = 25).

Examples:

• BP/25/0001 through BP/25/1846 — FY 25–26, sequential.
• BP/26/0001 onwards — FY 26–27, resets on 1 April 2026.

10–11 characters, readable, GSTN-compliant, reset-safe.

How Blueprint handles this

Blueprint's invoice module numbers RA bills and invoices sequentially within the April–March financial year automatically. Counter resets at 00:00 IST on 1 April. Prefixes are configurable per organisation. Cancellations leave the number in the ledger with status cancelled — no gaps.

If you're migrating from a calendar-year ERP, the billing module's migration tool imports your historical sequence with its original numbers preserved; new invoices number from where the FY sequence left off.

Further reading

• RA bills in construction
• CGST vs SGST vs IGST