Invoice Number Settings
Choose a format
Result
Your output will appear here.
This invoice number generator creates a batch of invoice numbers from your prefix, starting number and digit length, in sequential, year, year and month, or random code formats. It suits freelancers and small businesses setting up or fixing a numbering system. It is free, needs no sign-up, and runs in your browser, so you can copy the list straight into your records.
Choose a format
Your output will appear here.
Start every number with your own letters, such as INV, a client code or a brand initial.
Continue from your last invoice instead of starting at 1, so the series stays unbroken.
Set the number of digits so INV-0009 sorts before INV-0010 in folders and spreadsheets.
Choose sequential, year plus sequence, year and month plus sequence, or a random code.
Three steps from a blank form to a result you can use.
Type a prefix and the first number you want, usually one more than your last invoice.
Pick how many numbers you need, the digit length, and one of four formats.
Click Generate Numbers, check the list, then copy it into your invoice log or spreadsheet.
An invoice number is the one detail every invoice needs and the one that causes the most trouble when it repeats or skips. This page explains which format to pick and the rules worth following.
| Format | Looks like | Best for | Watch out for |
|---|---|---|---|
| Sequential | INV-0001 | Most small businesses and freelancers | Pick enough digits for growth |
| Year + sequence | INV-YYYY-0001 | Businesses that file by tax year | Decide whether the counter resets each year |
| Year/month + sequence | INV-YYYYMM-0001 | High volume or monthly billing | Longer numbers for clients to quote |
| Random code | INV-A7K2QZ | Internal references or order codes | Not sequential, so not suited to VAT invoices |
We suggest plain sequential numbers unless you have a reason for dates. They are short, easy to quote on the phone, and gaps are obvious at a glance.
GOV.UK lists a unique identification number as the first item every UK invoice must include. For VAT invoices, HMRC goes further: VAT Notice 700/21 asks for a sequential number based on one or more series that uniquely identifies the document. Other tax authorities set similar rules, so a clean sequence protects you wherever you trade.
The Random code format creates unique codes, but they do not run in order. Use it for internal or order references, not for UK VAT invoices.
The right system depends on how many invoices you send and who needs to read the numbers. These are common set-ups we see, and the settings that produce them.
| Business | Set-up | Generator settings |
|---|---|---|
| Freelancer with a few clients a month | One simple series | Prefix INV, 4 digits, Sequential |
| Agency with retainer clients | One series with the year for filing | Prefix INV, 4 digits, Year + sequence |
| Online shop with many orders | Monthly blocks that stay unique | Prefix INV, 4 or 5 digits, Year/month + sequence |
| Business with two trading brands | One series per brand | Prefix per brand, such as NB and SW, Sequential |
| Any business issuing credit notes | Separate credit note series | Prefix CN, 4 digits, Sequential |
Some businesses put a client code in the prefix, such as ACME-0001. That helps when you look up one client, but it creates many short series. If you go this way, keep a master log so each number stays unique across the business. For most small teams, we prefer one main series and a client reference written on the invoice itself.
Example: a freelance copywriter has sent 41 invoices numbered 1 to 41 and wants a tidier format without breaking the series. This is an illustration.
The result runs from INV-0042 to INV-0051. The counter continues from 41, so there is no gap, and the four digits leave room for 9,999 invoices before the length changes.
If she later switched to Year + sequence, we would keep counting from the last number rather than restarting, unless her accountant prefers a yearly reset.
Quick answers about the Invoice Number Generator.
A short prefix plus a zero-padded sequential number, such as INV-0042, works for most small businesses. It is easy to quote, easy to sort, and any gap is obvious. Add a year or month only if you file invoices by period or send a high volume each month.
For UK VAT invoices, yes. HMRC asks for a sequential number based on one or more series that uniquely identifies each invoice. For other UK invoices, GOV.UK requires a unique identification number. We suggest sequential numbering everywhere, because it makes missing or duplicate invoices easy to spot.
Yes. A letter prefix such as INV, a client code, or a document type like CN for credit notes is common. Keep the prefix the same within a series. The Prefix field adds your letters to every number, and the Random code format mixes letters and digits for internal references.
It is a choice, not a rule. A continuous series is the simplest to manage. If you use the Year + sequence format, each number carries the year, so you can restart the counter annually without creating duplicates. Ask your accountant which they prefer for your records.
Do not reuse it. Keep the cancelled invoice on file marked as void, and if it was already sent, issue a credit note with its own number. Reusing numbers creates two documents with the same reference, which makes your records hard to audit and confuses clients.
No. It creates a list from your settings each time and does not save anything. Keep your own log or spreadsheet of numbers sent, and check it before you set the Starting number for the next batch so the series stays unbroken.
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