Invoice Number Generator
Generate sequential invoice numbers with a custom prefix, date token, numeric counter, and suffix. Choose your separator, padding, and step size, then copy individual numbers or download the whole batch as TXT or CSV. Everything runs in your browser — no uploads, no signup.
Build your format
A short code that identifies your company or the document type.
What is an invoice number generator?
An invoice number is the unique identifier printed on every invoice you send. It is how you, your customer, and — if it comes to it — a tax auditor refer to a specific document years later. An invoice number generator produces these identifiers in a consistent pattern so you never have to think about them one at a time.
Most accounting systems expect you to supply your own invoice numbering sequence. Small businesses, freelancers, and consultants often do this in a spreadsheet, which is fine until two invoices accidentally get the same number. A pattern-based generator removes that risk: you pick the format once, generate a batch, and use the numbers one after another.
This tool gives you full control over the format. You can put a date token at the start, put a company prefix before that, add a suffix at the end, and pad the counter to any width. Every generated number is unique within the batch, and the counter advances by whatever step you choose.
How to use the generator
- Enter a prefix (optional). Most businesses use a short code like "INV", "INV-", or their company initials. This makes it obvious what the number refers to when someone reads it out of context.
- Choose a date token (optional). Adding the year and month makes it easy to spot how old an invoice is. YYYYMM is the most common choice for small businesses; YYYYMMDD is useful if you generate many invoices per day.
- Pick a separator. A hyphen is the most readable. Some accounting systems disallow certain characters, so check your software's rules if you're importing numbers into a system.
- Set the starting number. If you're picking up where you left off, use the Continue button — it will pre-fill the field with the number immediately after your last generated one.
- Set the padding. Padding means the counter is left-padded with zeros to a fixed width. Four digits gives you 0001 through 9999; five digits gives 00001 through 99999. Pick a width big enough that you won't outgrow it in a year.
- Pick a step size. A step of 1 gives consecutive numbers. A step of 10 or 100 leaves gaps that some businesses use to separate invoice series, or to leave room for manual insertions later.
- Set the quantity. Up to 200 numbers per batch. Each generated number is saved locally so you can come back and continue from the right place.
- Generate and copy. Click Generate, then copy individual numbers or the whole batch. Download as TXT for simple lists, or CSV for Excel and Google Sheets.
Invoice numbering best practices
Keep it sequential
Most tax authorities recommend gapless sequential numbering. If a number is missing, it looks like an invoice was lost or deleted — which invites questions you'd rather not answer.
Anchor it to time
Including the year (and often the month) in the number makes it easy to sort invoices chronologically and to see at a glance which tax period a document belongs to.
Never reuse a number
Once an invoice number has been assigned, it belongs to that invoice forever. If you cancel an invoice, keep the number and issue a credit note — do not reissue the original number to a different customer.
Be consistent
Pick a format and stick with it. Mixed formats across a single tax year cause accounting headaches, and some jurisdictions require a single continuous series per business entity.
Back up your log
Keep a spreadsheet or export of every invoice number you've issued, alongside the customer name, invoice date, and total. This is what auditors ask for, and it's much easier to maintain if you never had to reconstruct it.
Prefix for clarity
If you issue multiple document types — invoices, quotes, credit notes — give each a different prefix. INV, QTE, and CRN tell everyone what the document is before they read a single line of it.
Date token reference
Each token is replaced at generation time with the current date. The generated batch uses the same date for every number, so all invoices created today share the same YYYYMM segment.
| Token | Example (18 Oct 2024) | Best for |
|---|---|---|
YYYY | 2024 | Annual invoice series |
YYYYMM | 202410 | Monthly invoice series — the most common choice |
YYYY-MM | 2024-10 | Readable version of YYYYMM |
YYYYMMDD | 20241018 | High-volume invoicing where daily batches are common |
YYYY-MM-DD | 2024-10-18 | When the date needs to be visible in the number itself |
YY | 24 | Compact format for short invoice numbers |
YYMM | 2410 | Compact monthly series |
MMYY | 1024 | Regional format (used in some US workflows) |
DDMMYY | 181024 | Regional format (common in the UK and India) |
A note on legal requirements
Invoice numbering requirements vary by country. The EU, UK, India, Australia, and most US states all have their own rules about whether invoices must be numbered sequentially, whether gaps are allowed, and what other identifiers (tax ID, VAT number, business registration) must appear on the document. Check your local regulations before finalizing a format.
This tool generates the number itself — it does not check that your format is compliant with your jurisdiction. If you are unsure, the safest approach is a simple, gapless, sequential series with a consistent prefix, no gaps, and a separate log of every number you have issued.