As a freelancer or entrepreneur, you must assign a unique, sequential number to every invoice. This is not just a tax requirement—it also keeps your own records organized and clear.

What is an invoice number?

An invoice number is a unique code you assign to each invoice. It’s required—even if you’re not VAT-registered. It helps you and your client find invoices later and keeps your records in order.

Examples of good invoice numbers

• 2025-001
• 2025-002
• 2025-003

You can also use initials or project codes, as long as the system is logical and continuous:

• DEV-2025-001
• WEB-2025-001

What not to do

Never reuse an invoice number. Avoid skipping or reversing numbers (e.g., 2025-010 to 2025-004). These errors raise red flags during audits.

How to stay organized

Using a tool like InvoiceTimer? It automatically generates invoice numbers based on your settings (e.g., year + sequence). You never have to remember the last number—it’s all automated.

Extra tips

• Start a new sequence each year (e.g., 2025-001)
• Use prefixes per client or project
• Save invoices digitally and in the cloud

With InvoiceTimer, invoice numbers are auto-generated and follow a clear sequence. That’s handy for you—and your accountant.