InvoiceGenerator

How to Number Invoices (and Never Break the Sequence)

Invoice numbers look trivial until an audit, a duplicate, or a VAT inspection. One simple sequence rule prevents all three.

Quick answer: Number invoices sequentially without gaps — a year prefix (2026-001) is the simplest system that scales. Never reuse or renumber, and keep proformas, credit notes and receipts in their own sequences.

Systems that work

  • 2026-001, 2026-002 — year prefix, simplest
  • INV-2026-0001 — adds a document-type tag
  • Client code + sequence (ACME-014) — only if you never mix tax entities

What breaks sequences

  • Drafts sent before numbering — number at send time, not before
  • Deleted invoices — cancel with a credit note instead of deleting
  • Multiple legal entities on one sequence — one sequence per entity, always

Proformas and credit notes

Give proformas their own PI- sequence so they never collide with real invoices. Credit notes get a CN- sequence and reference the invoice they correct.

Frequently Asked Questions

Are gaps in invoice numbering a problem?
Yes — tax authorities read gaps as deleted invoices. If you cancel, issue a credit note; never just delete.
When exactly do I assign the number?
At the moment the invoice leaves you (printed or sent). The generator assigns numbers in your sequence and keeps the last one in browser storage.

Related Tools & Guides

Invoice GeneratorBlank Invoice Template