How to number invoices
An invoice number is how you and your client refer to a specific invoice. A simple system keeps records easy to search and easy to audit.
Why numbers matter
Numbers let both sides find an invoice quickly, match payments to invoices, and spot anything missing. Many accounting systems and clients' payables teams use them to track what has been paid.
Systems that work
- Running number: 0001, 0002, 0003
- Year and number: 2026-001, 2026-002
- Client code and number: ACME-001, ACME-002
- Date based: 20261013-1
Rules to keep
- Make every number unique
- Do not reuse numbers, even for cancelled invoices
- If you void an invoice, keep the number and mark it void
- Use the same format across all your invoices
Do you have to start at 1?
No. Some freelancers start at a higher number so a new business looks established. Whatever you choose, keep it consistent and do not fabricate history.
Questions
Can I change my numbering system?
Yes, but do it at a clean break, such as the start of a year, and keep a note of the change.
Should receipts use the same sequence?
Many people use a separate series for receipts, such as RCT-0001, so the two stay easy to tell apart.
Free tool: Invoice Number Generator
Free, no signup. Download as a PDF.
General information, not legal, tax, or accounting advice. Rules vary by place.