Invoice number generator

How to create an invoice numbering scheme

1. Pick a prefix. Use letters like INV, your initials or a client code. Leave it blank for plain numbers.
2. Choose the structure. Add the year, the month or both, choose a separator and a padding length such as 4 digits.
3. Set the first number. Enter the number to start from. If you already have invoices, continue from your last one.
4. Preview the sequence. The generator shows ten numbers in a row. Check they look right and are unique.
5. Copy a number into your invoice. Copy the next number and paste it in the invoice. The invoice generator can also increase the number automatically.

Why invoice numbers matter

An invoice number is a unique reference for one invoice. It lets you and your customer find the document, match a payment to it, and keep your records in order. Tax authorities also care about it: in many countries, the invoice number is a required element. In the EU, VAT rules require a sequential number that uniquely identifies the invoice, and it may use one or several series. The UK requires a unique identification number that follows on from the number of the previous invoice. The US has no federal numbering rule, but a consistent scheme helps with audits and accounting.

Whatever the rule, the principles are the same: every number is unique, you never reuse one, and gaps can be explained. If you need to cancel an invoice, issue a credit note rather than deleting the original.

Common invoice number formats

Pick a format that you can keep using for years. If you restart numbers each year, the year must be part of the number, or numbers will repeat.

Rules to follow

• Unique: never use the same number twice.
• Sequential: go up in order, which makes missing invoices easy to spot.
• Readable: avoid long strings of random characters and avoid characters that confuse, such as the letter O and the number 0.
• Don’t reveal your size: starting at 0001 shows that you are new. Some people start at 1000 for this reason. This is a choice, not a requirement.
• Separate documents: use different prefixes for quotes, credit notes and proforma invoices.
• Consistent: change a scheme only at the start of a new period, and keep a note of the change.

The legal specifics depend on the country. Check the page for your country: the UK, EU, Australia and Canada pages list what your invoice must contain. Our guide to invoice numbering best practices goes into more detail.

Gaps, mistakes and cancelled invoices

If you find a mistake after you have issued an invoice, do not edit the old one in place and do not reuse the number. Issue a credit note that cancels or reduces the original, then issue a new invoice with the next number. If a number was reserved but never sent, record the reason. Auditors prefer a documented gap to an unexplained one.

If you run more than one business or use several invoicing tools, keep one series for each business so numbers cannot clash. The invoice generator lets you save separate business profiles with separate numbering.

Tips for freelancers and small businesses

• Start simple, such as INV-0001. You can add the year later if your volume grows.
• Write the number in your bookkeeping record and on the bank reference so payments match.
• Use the invoice number as the payment reference you ask clients to quote.
• Keep a copy of every invoice, whether paid or not, for the legal retention period. See how long to keep invoices.

Glossary

Invoice number

A unique reference that identifies one invoice.

Sequential

Numbers that follow one another in order.

Prefix

Letters at the start of a number, such as INV.

Padding

Leading zeros that keep the number a fixed length.

Credit note

A document that cancels or reduces an earlier invoice.

Related topics

• invoice number generator
• invoice numbering
• invoice number format
• sequential invoice numbers
• invoice number examples
• INV-0001
• invoice series
• unique invoice number
• invoice reference
• invoice numbering rules