An Invoice ID is a unique number or code assigned to each invoice you send. It is how you and your client reference a specific bill, track payment status, and keep your bookkeeping organized.

Why every invoice needs an ID

Without a unique identifier, matching incoming payments to the right job becomes difficult, especially when you send multiple invoices to the same client. An Invoice ID solves that instantly. When a client pays and references INV-2026-0042, you know exactly which invoice cleared.

Tax authorities in most countries require sequential or unique invoice numbering. Gaps or duplicates in your numbering can raise questions during an audit, so pick a system and stick with it.

How to structure invoice IDs

Common formats include:

• Sequential numbers: 001, 002, 003

• Year-based: 2026-001, 2026-002

• Prefix plus number: INV-0042, FACT-2026-15

The format matters less than consistency. Choose one approach, never reuse a number, and include the Invoice ID on every invoice you issue.

Invoice IDs and payment tracking

When a payment arrives in your bunq Business Account, compare the amount and reference against your invoice list. Instant notifications mean you can mark invoices as paid the moment money lands, keeping your records current without delay.

Common questions

Can I skip numbers in my invoice sequence?

Avoid gaps when possible. If you void an invoice, keep a record of why the number was skipped. Some tax authorities require continuous numbering with documented exceptions.

Should the Invoice ID appear on the payment reference?

Yes, ask clients to include it when they pay. It makes reconciliation automatic and saves time on both sides.