How to number invoices correctly
Invoice numbering looks like the most boring decision on the invoice. It's also the one most likely to cause you a problem two years from now.
Why the sequence matters
The invoice number isn't for you. It's for everyone who has to verify later that your records are complete — a tax inspector, an accountant, your client's accounts payable, and future you, trying to work out which invoice a payment settled.
Most jurisdictions require invoice numbers to be unique and to form a continuous sequence with no unexplained gaps. The reason is simple: if you could freely delete invoices, you could remove income from the record and nobody could tell. A gap in a sequence is a question, and questions during an audit cost time even when the answer is innocent.
The practical failure modes are mundane:
- Duplicating last month's invoice and forgetting to change the number, so two different clients hold invoice 041.
- Deleting a mistake instead of voiding it, leaving a hole.
- Running two businesses through one sequence, so both sets have gaps.
- Restarting at 1 in January without the year in the number, creating duplicates a year apart.
Formats that work
| Format | Example | Good for |
|---|---|---|
| Plain sequential | 0042 | Very low volume; simple but says nothing |
| Year + counter | 2026-0042 | Most freelancers — sorts correctly, restarts cleanly |
| Prefix + year + counter | INV-2026-007 | Anyone running more than one company |
| Year + month + counter | 2026-07-004 | High volume, where finding by month helps |
Whichever you pick:
- Zero-pad the counter. Without padding,
10sorts before9in every file browser you'll ever use. - Put the year first within the identifier. Sorting alphabetically then equals sorting chronologically.
- Avoid slashes.
2026/07is a legal invoice number and an illegal filename on several systems. - Don't encode the client. Tempting, but it breaks the moment a client renames itself, and it leaks your client list into any filename you send around.
The rules worth following
- Never reuse a number. Not even for a corrected version of the same invoice — issue a new number and reference the old one.
- Never delete an issued invoice. Void it instead.
- One sequence per legal entity. Two businesses, two sequences. More on multiple companies.
- Pick a format and keep it. Changing format mid-year makes the sequence hard to demonstrate as continuous.
- Number at the point of issue, not when you start drafting — otherwise abandoned drafts eat numbers and create gaps.
Voiding and cancelling
You will, at some point, send an invoice with the wrong amount on it. The instinct is to delete it and pretend it never happened. Don't.
Mark it voided. The number stays in the sequence, the record shows the invoice existed and was cancelled, and there's no gap to explain. Then issue a corrected invoice with the next number, and — if it's already with the client — say plainly in the email that it replaces the earlier one.
Void vs delete, concretely
Deleting invoice INV-2026-007 leaves your records jumping from 006 to 008 with
nothing to show why. Voiding it leaves 007 present, clearly marked, unpaid, and
uncontroversial. The second version takes the same amount of effort and answers the
question before it's asked.
Setting it in the app
In Quick Invoice Generator PDF
- Settings → Invoice Customizations → Number Format. Pick a format; each option shows a live example of what your next number will look like.
- New invoices are numbered automatically from the sequence — you can override it on an individual invoice if you need to, but the default keeps the run intact.
- To cancel one, press and hold it in the invoice list and set its status to Voided rather than deleting it.
- Running two businesses? Each company keeps its own independent sequence, so they can't collide.
Let the numbering take care of itself
Pick a format once and every new invoice continues the sequence — with voiding instead of deleting.
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Frequently asked questions
Do invoice numbers have to be sequential?
In most jurisdictions, yes — invoice numbers must form a unique, unbroken sequence with no unexplained gaps. The rule exists so that a tax authority can tell whether an invoice has been quietly removed from the record. Requirements vary by country, so check yours.
What is a good invoice number format?
Something sortable, unambiguous and zero-padded — INV-2026-007 or 2026-0042. Include the year so sequences restart cleanly, pad the counter so files sort correctly, and avoid slashes, which break filenames on some systems.
What do I do if I need to cancel an invoice?
Don't delete it and don't reuse the number. Mark it as voided so the number stays in the sequence with a clear record of why. Deleting an invoice leaves a gap you'll have to explain later.
Can I restart numbering each year?
Yes, provided the year is part of the number so each invoice identifier stays unique overall — 2026-001 following 2025-118 is fine. Restarting at 001 with no year is not, because you'd have two invoices with the same identifier.