Free invoicing tool · no signup
Invoice number generator
Build a series you can defend two years from now: pick a prefix, a year segment and a padded counter, then copy the batch or export it as CSV. Deterministic, gap-free, and generated entirely in your browser.
Your series
10 numbers · next will be INV-0011
- INV-0001
- INV-0002
- INV-0003
- INV-0004
- INV-0005
- INV-0006
- INV-0007
- INV-0008
- INV-0009
- INV-0010
Nothing is stored or uploaded — closing the page discards the batch.
Which invoice numbering scheme should you use?
There are only three schemes worth considering, and all of them share one property: from the last number, the next one can be calculated. That is what makes a series searchable and auditable.
| Scheme | Looks like | Best for | Watch out for |
|---|---|---|---|
| Continuous | INV-0042 | Small businesses that want the simplest possible trail | Nothing — as long as the counter never resets |
| Year-prefixed | INV-2026-0042 | Businesses that search records by period | Deciding at year-end whether the counter restarts, then doing it inconsistently |
| Type-prefixed pair | QUO-0042 / INV-0031 | Anyone who sends quotes before invoices | Assuming quotes and invoices share a counter — they should not |
Whichever you pick, generate the batch before you need it and start at a number higher than anything you have previously issued. Starting at 1001 to look established is harmless; starting at 1001 and later issuing 42 is not.
Padding, separators and sorting
Padding exists so numbers sort correctly as text. Without it, a spreadsheet or file listing puts 10 before 9, and 100 before 11. Four digits covers 9,999 documents; five covers 99,999. Pick a width you will not outgrow, because widening later changes every subsequent number.
The separator is cosmetic but should be consistent: a hyphen is safe in filenames and URLs, while a slash is not — INV/2026/0042 becomes a path in a filename and a broken link in a URL. Avoid spaces and ampersands for the same reason.
Gaps, voids and year-end resets
If an invoice is cancelled before it is sent, keep the number and mark the document void. A documented gap is normal; a reused number is not. The test an auditor applies is simple: can each number in the series be explained? “Voided — duplicate of 0041” is an explanation. Silence is not.
At year-end you have two safe options: keep counting (INV-2027-0188 in January) or restart with the new year visible in the prefix (INV-2027-0001). What makes either option safe is that the last number of the old year is recorded and the first number of the new year is issued before any work begins. Retro-numbering a busy January is where duplicates are born.
The full set of rules — including what to do when two invoices accidentally share a number — is in our guide to how to number invoices.
Frequently asked questions
Do invoice numbers have to be sequential?+
In most jurisdictions there is no rule that every integer must appear, but a tax invoice issued by a registered vendor usually needs a unique, unbroken serial number. Sequential is the simplest scheme that satisfies both the legal requirement and your own ability to find a document later.
Can I restart invoice numbers every year?+
Yes, if the year is part of the number — INV-2027-0001 makes the reset visible. Restarting the counter without changing the label is what creates duplicates, because two documents end up with the same number in the same series.
What should I do if an invoice number is skipped?+
Leave the gap visible and note why. A number can be skipped because an invoice was voided, a draft was abandoned or a document was cancelled. Quietly reusing the number is the mistake; auditors can reconcile a documented gap, but not two invoices claiming the same number.
Should quotes and invoices share a number series?+
No. Use a separate prefix and counter — QUO-0042 and INV-0031 — so a client can tell what kind of document they are holding without opening it. It also means converting a quote does not consume an invoice number that was never sent.
How many digits should an invoice number have?+
Enough that you will not run out and that sorting works as text. Four digits covers 9,999 documents; five covers 99,999. Padding matters more than length: 0042 sorts correctly, while 42 sorts before 7 in a spreadsheet.
Does the invoice number need a prefix?+
No, but a prefix helps. INV, TAX or a short business code tells you at a glance what the document is, and prevents a quote number from colliding with an invoice number when both are searched together.