Free Invoice Number Generator

This invoice number generator builds a clean run of invoice numbers from your prefix, date and starting number. Copy the list in one click.

Number Format

Prefix

Separator

Date

Starting Number

Number of Digits

How Many to Generate

Your Invoice Numbers

INV-0001
INV-0002
INV-0003
INV-0004
INV-0005
INV-0006
INV-0007
INV-0008
INV-0009
INV-0010

How to generate invoice numbers

The generator above builds the whole list as you type, so you can try a few styles before you pick one. Each list is a run of sequential invoice numbers with no gaps.

Type a short prefix such as INV, or a client code, and choose a separator.
Choose whether to add the year or the year and month, then set the starting number and how many digits to pad it to.
Choose how many numbers you need, then copy the list in one click and paste it into your records or your invoicing tool.

Already sending invoices? Set the starting number to one more than your last invoice, so the new list carries straight on from the old one.

Invoice number formats with examples

Most small businesses use one of three invoice number formats. Each invoice number example below comes straight from the generator, and the date-based style takes its year and month from today's date:

Three common invoice number formats
Format	Example	When it suits
Plain sequence	INV-0001, INV-0002	Most small businesses. Simple, short and easy to read out on the phone.
Date based	2026-10-001, 2026-10-002	Businesses that restart the count each month or year, or file invoices by date.
Client code	ACME-001, ACME-002	Freelancers with a few regular clients who want each client's invoices grouped.

Whichever format you choose, keep it for good. Switching styles halfway through a year makes your records harder to follow and raises questions from your accountant.

Avoid styles that cause trouble later. A number made only from the date clashes as soon as you send two invoices on one day, and a random number makes a missing invoice impossible to spot.

Rules for numbering invoices

Every number is unique. No two invoices may share a number, even for different clients.
The numbers run in order. Each new invoice takes the next number, so a gap stands out straight away.
A number is never reused. If you cancel an invoice, keep its number on record as cancelled and give the replacement a new one.
The number travels with the invoice. Quote it on any credit note, receipt or reminder for that invoice, so each one can be matched to the right bill.

If you also number quotes or credit notes, give each series its own prefix, such as QUO or CN, so the series never overlap.

These rules let you, your client and a tax inspector find any invoice quickly and see that none are missing. For more on setting up and fixing a numbering scheme, read our guide to choosing an invoice numbering system.

Frequently Asked Questions

Is this invoice number generator free?

Yes. It is free with no sign-up, and you can generate as many lists as you need.

Do invoice numbers have to be sequential?

Every number must be unique. Tax rules in many countries also expect the numbers to follow a sequence, so keep them in order and do not skip or reuse any.

Can invoice numbers have letters?

Yes. A short prefix such as INV, or a client code, is common and makes the numbers easier to recognise.

Should I restart invoice numbers each year?

You can, as long as the year is part of the number, for example 2026-001. That keeps every number unique.

What number should my first invoice be?

Any number you like. Many businesses start at 1001 instead of 1. Just carry on in order from there.