Wazi Invoices · Practical guide
Invoice numbering: a simple system you can maintain
Use one distinct reference for each invoice you issue. Pick a format you can maintain, keep a register, and check the next reference before sending. A quote number, purchase order and payment reference each have a different job.
By Jonty Stander · Updated · General business workflow guidance
Pick a format that stays clear as you grow
Start with the simplest format that separates your invoice records reliably. Adding a year can help when you review older work; extra codes are only useful if everyone issuing invoices understands them. Keep the written convention with your records.
| Example format | How to read it | What to decide |
|---|---|---|
| INV-0001 | One continuous invoice sequence | How many digits to reserve as the sequence grows. |
| INV-2026-0001 | Year plus sequence | Whether the sequence restarts each year; the full reference must stay distinct. |
| STUDIO-2026-0001 | Business or team prefix, year and sequence | Who controls each sequence and how duplicate references are prevented. |
Fictional numbering example
After INV-2026-0041, the next reference in the same sequence is INV-2026-0042. If your documented convention restarts each year, INV-2027-0001 is distinct from INV-2026-0001 because the full reference includes the year.
Keep a small invoice register
A register makes a numbering convention useful. Before issuing a document, check what has already been used. This is especially important if two people, multiple browser tabs or more than one tool can issue invoices.
- Record the complete invoice reference, issue date, customer or job reference, amount, due date and status in your own appropriate business records.
- Assign the next reference using a single controlled process. A shared register or invoicing system is safer than independent counters on several devices.
- Keep the issued PDF with its record. Record the associated quote or purchase order separately so you can trace the job.
- Track cancelled, superseded or corrected records rather than reusing an old number for a different invoice. Seek accounting advice about how to correct an issued invoice in your jurisdiction.
Keep these references separate
| Reference | Purpose |
|---|---|
| Invoice number | Identifies your request for payment. |
| Quote number | Identifies the proposed work and price. |
| Customer purchase order | Identifies the customer’s internal authorisation or order. |
| Payment reference | Helps match a payment to your records. It can use the invoice number when appropriate. |
A second PDF is not automatically a second invoice
Downloading the same invoice again should not create a new claim for the same payment. Keep the reference when you resend an unchanged issued document, and make clear that it is a copy. A genuinely different invoice needs its own reference.
Do not assume that a number displayed in an empty builder has been reserved for your business. Check your existing records before sending, including documents made in other tools.
Check the number before downloading in Wazi
The builder lets you edit the document number. Replace the suggested reference with the next reference from your own records and check it again in the PDF. The payment reference can follow the document number, so verify that it is the reference you want the customer to use.
A free Wazi account can save invoices and quotes. It does not remove the need to reconcile references across other tools and your business records. This guide does not claim that Wazi reserves guest numbers globally or checks every external invoice for duplicates.
Sources and scope
Sources checked on 18 October 2026. The examples and suggested record-keeping steps are Wazi’s practical guidance. Legal and tax requirements depend on your location and circumstances; use the relevant authority or a qualified adviser for those decisions.
Business Victoria: Write an invoice
Practical background on distinct invoice references and customer/order information. Australian tax rules are outside this guide’s scope.
GOV.UK: Invoice information
UK guidance includes a unique identification number. The examples here are a suggested workflow, not a statement of South African tax compliance.
Put it into practice
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