Articles on: Customer communication

Set your invoice numbering

Most countries require invoices to carry sequential numbers. Set the format under Features → Invoices → Numbering. Do this before you issue any invoices — once a format has produced numbers, its starting number is fixed.

What this does

An invoice number is not decoration. Accountants and tax authorities expect a sequence with no gaps and no repeats.

Set the format

Go to Features → Invoices → Numbering.
Turn on Turn on invoice numbering.
Set the parts:

Prefix — Letters at the start, like INV
Year format — Short year, full year, or none
Separator — Dash, slash, or others
Starting number — Where the sequence begins
Number length — How many digits, padded with zeros

Check the Preview and the Example sequence.
Save.

The part to get right first

Once a format has issued numbers, its starting number is fixed.

The page tells you which state you are in:

"This format has not issued any invoice numbers yet" — you can still change the start.
"This format has already issued invoice numbers, so its starting number is fixed" — you cannot.

To choose a new starting number after that, you have to change the prefix, year, separator or zero-fill. That starts a separate sequence.

So decide your format before your first invoice. Changing it later is possible, but you end up with more than one sequence running.

Each format keeps its own count

You can change the prefix, year, separator and number length at any time. Each combination keeps its own count.

Switching back to a format you used before resumes where it left off. That is deliberate — it stops you accidentally reissuing numbers.

Numbers already printed on invoices never change.

The repeat warning

If you re-use a prefix and set a starting number below what that prefix already reached, the page warns you:

"You have used the prefix INV before and reached 1240. Starting at 1000 can produce numbers that look like ones you have already issued."

Take that seriously. Duplicate invoice numbers cause real problems in an audit.

Good to know

Set this up before you go live. It is the one invoice setting that is awkward to change afterwards.

Include the year if you file annually. Many accountants prefer a sequence that restarts each year, and a year in the format makes that natural.

Zero-padding is cosmetic but expected. INV-0001 sorts and reads better than INV-1.

Check your local rules. Some countries require strict sequences with no gaps at all. What is acceptable varies.

Troubleshooting

The starting number is greyed out — Why: That format has already issued numbers — Fix: Change the prefix, year or separator to start a new sequence
Numbers restarted unexpectedly — Why: You changed the format — each keeps its own count — Fix: Switch back and it resumes
A duplicate-number warning — Why: The prefix was used before and reached higher — Fix: Start above the previous highest, or use a new prefix
Invoices have no number — Why: Numbering is off — Fix: Turn on Turn on invoice numbering
The preview does not match — Why: Changes are unsaved — Fix: Save, then re-check

FAQ

Can I change the starting number later?

Only if that exact format has not issued any invoices yet. Otherwise change the prefix, year, separator or zero-fill, which starts a separate sequence.

What happens to invoices already issued?

Nothing. Numbers already printed never change.

Should the year be in the number?

If your accounts run yearly, yes. It makes each year a natural sequence.

What if I re-use an old prefix?

The count resumes where that format left off, so you do not get duplicates. If you force a lower starting number, the app warns you.

Do I need invoice numbering at all?

In most countries, yes, if you issue invoices. Check your local rules.

Updated on: 21/08/2026

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