Invoice numbering policy: what works, what causes chaos?

Number sequences in 2026 might sound futuristic, but in practice I see an SMB struggling with missing or duplicate invoice numbers every single week. Here are the three patterns that actually work.

The Dutch Tax Authority requires invoices to be "consecutively numbered" per invoice series. In practice, that leaves room for three workable patterns.

Pattern 1: one running sequence per year

2026-0001, 2026-0002, 2026-0003… Reset at the start of each calendar year.

Pro: simple, perfectly fine from a tax perspective.

Con: the jump in numbering at the turn of the year can look confusing to clients.

Pattern 2: one ever-running sequence

000001, 000002, …, 003847, 003848. Never reset.

Pro: no year-end jump, visually consistent.

Con: numbers become unwieldy at high values. After a few years you end up with numbers that have spiralled out of hand.

Pattern 3: a sequence per product type

SUB-2026-0001 for subscriptions, PROJ-2026-0001 for project work, CON-2026-0001 for consultancy hours.

Pro: easier analytics per series.

Con: more complex during a tax audit — you must be able to demonstrate that each series is consecutive.

What you should never do

• Separate numbering per client. Not permitted.
• Random numbers or codes with no chronological logic.
• Entering numbers manually — always generate them automatically.

When mistakes happen

Sent an invoice with the wrong number? Raise a credit note against that invoice and issue a new one with the correct number. Never skip a number or use one twice.

See also: invoicing complete guide.