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Invoice Number Generator

Pick a format, type your prefix and starting number, and this generator builds up to 100 unique invoice numbers such as INV-0001, INV-202610-0001 or INV-2026-0001. Copy the list or download it as a CSV. Everything runs in your browser and nothing is saved.

Best for: Freelancers and small businesses setting up a numbering scheme, or moving from ad-hoc numbers to one consistent series.

Add a client code here (INV-ACME) or leave it blank.

Your Invoice Numbers

INV-0001
INV-0002
INV-0003
INV-0004
INV-0005
INV-0006
INV-0007
INV-0008
INV-0009
INV-0010

The year and month come from your device's date. Numbers are unique within this list only: the tool does not remember numbers you generated or issued before.

Which invoice number format should you use?

Use a plain sequential series unless you have a reason not to. It is the shortest, and it never has to change. Add the year if you want each year's invoices to group together, and the month only if you send many invoices a month and file them monthly.

FormatExampleBest forTradeoff
SequentialINV-0042Most freelancers and small businessesShows roughly how many invoices you have sent
YearINV-2026-0042Filing and tax returns by yearYear in the number must match the invoice date
Year and monthINV-202610-0042High volume, monthly reconciliationLongest to read out on a phone call
Client code in the prefixINV-ACME-0042A few clients with many invoices eachOne series per client to keep unique and in order

How the generator builds each number

Each number is your prefix, then the date part for the format you picked, then a counter padded with zeros to four digits, all joined with hyphens: PREFIX-[YYYY or YYYYMM]-NNNN.

Worked example: prefix INV-ACME, Year format, starting number 42, three numbers, generated on 27 October 2026. The counter 42 is padded to 0042, the year 2026 is inserted, and the result is INV-ACME-2026-0042, INV-ACME-2026-0043 and INV-ACME-2026-0044. The same inputs with the Year and month format give INV-ACME-202610-0042 onwards.

  • Past 9999 the counter simply grows a digit: INV-9999 is followed by INV-10000. Nothing is cut off.
  • Blank prefix: the number starts with the date or counter (0001), with no leading hyphen.
  • Decimals and negatives in the starting number are rounded down to a whole number of 0 or more.

What UK, EU and US rules say about invoice numbers

The UK and the EU set a rule on uniqueness and sequence, not on format. The US federal tax agency sets no numbering rule at all.

JurisdictionRuleOfficial source
United KingdomEvery invoice needs "a unique identification number". A VAT invoice needs a sequential number, based on one or more series, that uniquely identifies it.GOV.UK invoice rules; HMRC VAT Notice 700, 16.3.1
European UnionA VAT invoice must show "a sequential number, based on one or more series, which uniquely identifies the invoice". Member states can add detail.VAT Directive 2006/112/EC, Article 226(2)
United StatesNo federal invoice numbering rule. The IRS lists invoices among the supporting documents you should keep in an orderly way.IRS: What kind of records should I keep

"One or more series" means you can run separate sequences, for example one per year or per client, as long as each number is unique. This is general information, not legal or tax advice; check with your tax authority or an accountant. Last reviewed 27 October 2026.

What this generator can and cannot guarantee

Every number in one generated list is unique. That is the only guarantee, because the page stores nothing. Run it twice with the same inputs and you get the same numbers again, so if you generate a fresh list next month, set the starting number to one after the last invoice you actually sent.

  • No shared counter. Two people generating lists on two laptops can produce the same number. If more than one person invoices, keep a single counter in your invoicing software or a shared sheet.
  • Date from your device. The year and month formats use today's date on your computer, not the invoice date. Generate monthly numbers in the month you will use them.
  • Up to 100 at a time. Enough for a year of weekly invoices; generate another batch when you run out.

How InvoiceQuickly numbers invoices for you

If you create invoices in InvoiceQuickly, you do not need this generator. In Settings you choose a prefix (up to 10 letters, numbers, hyphens or underscores) and the next invoice number, and every new invoice gets PREFIX-0001, PREFIX-0002 and so on automatically, on the Free plan too. The next number cannot be set lower than the current one, and the same number cannot be saved twice in one account, which closes the two most common routes to a duplicate. Estimates are numbered EST- and credit notes CN-, and they share the same counter as invoices, so your invoice series can skip numbers where a quote or credit note was issued. Those gaps are explained by the matching EST- or CN- document. See pricing for what each plan includes.

When this isn't the right fit

Your invoicing or accounting software already numbers invoices. Keep its counter; pasting numbers from a second source is the usual way duplicates start.

You need to renumber invoices you have already sent, for example after an audit query. Talk to your accountant first: changing the number on an issued invoice breaks the link to payments and returns that already reference it.

Several people issue invoices at the same moment. A list made in a browser cannot reserve numbers; you need one shared counter that hands out the next number as each invoice is saved.

Frequently asked questions

Are invoice numbers legally required?

In the UK, GOV.UK lists a unique identification number as something every invoice must include, and a VAT invoice needs a sequential number that uniquely identifies it. In the EU, Article 226 of the VAT Directive requires a sequential number based on one or more series. The IRS has no federal rule on invoice number formats, but your invoices are supporting records, so a unique number makes them far easier to match to payments.

Can I start invoice numbering at any number?

Yes. Neither GOV.UK nor the EU VAT Directive sets a starting number, so INV-1001 is as valid as INV-0001. What matters is that each number is unique and the series continues in order from wherever you start.

Can I restart invoice numbers each year?

Usually, yes, as long as every number stays unique. Putting the year in the number (INV-2026-0001, then INV-2027-0001) keeps each yearly series distinct. Restarting at INV-0001 without the year would repeat numbers you already issued, so avoid that. Some EU countries add their own rules, so check with your tax authority if you are VAT-registered there.

What should I do if I issued two invoices with the same number?

Keep the first invoice as issued. Cancel the duplicate with a credit note or a void record, then reissue it under the next unused number and tell the client which number to pay against. Do not delete the duplicate from your records; a documented correction is easier to explain than a missing document.

Is it a problem if my invoice numbers have gaps?

A gap you can explain is normally fine. Gaps usually come from voided drafts or from software that shares one counter across invoices, quotes and credit notes. Keep a record of what happened to each skipped number so you can answer an accountant or tax officer quickly.

How do I auto-generate invoice numbers in Excel?

Put your prefix and a running counter in separate cells and join them. For example, with the counter in A2, the formula ="INV-"&TEXT(A2,"0000") returns INV-0001, and each new row uses the previous counter plus 1. Excel does not stop you from typing the same number twice, so check the column for duplicates before you send.

Is this invoice number generator free?

Yes. It runs entirely in your browser, needs no account and stores nothing. Copy the list or download it as a CSV file and paste the numbers into whatever you use to send invoices.

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