Random Invoice Number Generator
Example ID, drawn when this page was built
70403642 Tap an ID to copy it.
Random or sequential: which can go on an invoice?
| Where | What the text says (verbatim) | Source | Last verified |
|---|---|---|---|
| EU (VAT) | a sequential number, based on one or more series, which uniquely identifies the invoice | Council Directive 2006/112/EC, Art. 226(2) EU law; EUR-Lex consolidated text of 14 April 2025 | |
| UK (VAT) | a sequential number based on one or more series which uniquely identifies the document | HMRC VAT Notice 700/21, section 4.1 HMRC notice; the same words are in VAT Regulations 1995, reg. 14(1)(a) | |
| UK (VAT) | The ‘invoice number’ can be numerical, or it can be a combination of numbers and letters, as long as it forms part of a unique and sequential series. | HMRC internal manual VATREC5010 HMRC internal guidance | |
| UK (all invoices) | a unique identification number | GOV.UK, Invoices: what they must include Official guidance | |
| India (GST) | a consecutive serial number not exceeding sixteen characters, in one or multiple series, containing alphabets or numerals or special characters- hyphen or dash and slash symbolised as "-'' and "/" respectively, and any combination thereof, unique for a financial year; | CGST Rules 2017, Rule 46(b) Law; CBIC tax information portal | |
| US (federal) | Supporting documents include sales slips, paid bills, invoices, receipts, deposit slips, and canceled checks. | IRS Publication 583 (Rev. December 2024) IRS publication; it sets no invoice-number format |
How many different IDs your settings allow
With your current settings: — possible IDs (—).
Calculated chance that 1 random draw contains a repeat:—.
If you keep issuing IDs with these settings, the calculated chance of at least one repeat is — among 1,000 IDs and — among 10,000 IDs.
| Settings | Possible IDs | Repeat chance, 100 IDs | 1,000 IDs | 10,000 IDs |
|---|---|---|---|---|
| 6 digits | 1,000,000 (106) | 0.49% | 39.33% | more than 99.9999% |
| 8 digits | 100,000,000 (108) | 0.0049% | 0.5% | 39.34% |
| 8 hexadecimal characters | 4,294,967,296 (168) | 0.00012% | 0.012% | 1.16% |
| 8 letters and digits | 2,821,109,907,456 (368) | less than 0.0001% | less than 0.0001% | 0.0018% |
| 10 letters and digits, no look-alikes | 819,628,286,980,801 (3110) | less than 0.0001% | less than 0.0001% | less than 0.0001% |
| 12 letters and digits | 4,738,381,338,321,616,896 (3612) | less than 0.0001% | less than 0.0001% | less than 0.0001% |
About this page
The tool removes repeats within a batch, so every ID in a batch is different. Numbers you issued earlier need to be checked, for example by pasting them into the exclude box.
Numbering real invoices? Use the sequential Invoice Number Generator.
For VAT and GST invoices, the EU, UK and Indian texts below ask for a sequential (or consecutive) number, so a random ID on its own does not match their wording. HMRC’s internal manual allows letters and numbers, but only “as long as it forms part of a unique and sequential series”. The general GOV.UK list for all UK invoices asks for “a unique identification number”. For the US, the IRS publication below lists invoices among the records to keep and sets no invoice-number format.
Numbering lines only, not a full list of invoice requirements. Other countries have their own rules; check your tax authority. Full table: invoice numbering rules by country. General information, not legal or tax advice.
The number of possible IDs is the number of characters in the set raised to the length of the random part. A prefix and a date do not add any variety, because they are the same for every ID you make that day.
Pure arithmetic from the settings: possible IDs = characterslength; chance of at least one repeat among n draws = 1 − ∏(1 − i/N) for i = 0 … n−1, where N is the number of possible IDs. A chance above zero is never shown as 0%; very small values show as “less than 0.0001%”.
Using an ID in our free invoice generator: the Invoice # field is free text up to 50 characters, a pasted ID is used as typed, and nothing auto-increments.
When a random ID fits and when to use a sequential series
A random ID fits sample or test invoices, internal order or booking references, and documents where no sequential-number rule applies.
For VAT or GST invoices, use a sequential series. HMRC’s VATREC5010 answers the questions people usually have when they want a number that looks less like a count:
- Starting above 1 so the business does not look new (the question in HMRC’s manual uses Invoice no 1135):
Yes, as long as the invoice series runs consecutively from that point.
- A customer reference plus a consecutive number:
Yes, this would have the affect of creating a unique and sequential series.
[sic, as published] - Several series at the same time, for example per customer or per division:
Yes, it is acceptable to operate more than one sequence at the same time.
Source: HMRC internal manual VATREC5010 (internal guidance, UK VAT), last verified 2026-09-25.
To build the next number in a series (for example INV-2026-001), use the Invoice Number Generator. For how UK rules treat letters, gaps and credit notes, see how to number invoices in the UK.
How the IDs are generated
Everything runs in your browser and the IDs are not sent to us. The exclude list is compared in this page only and is not saved. Google Analytics receives the page view, an event saying the tool was used and, when you press a copy button, an event naming the kind of button; these events carry no ID, no setting and nothing from the exclude list. In the EEA, the UK and Switzerland, analytics cookies are set only if you accept them, and while consent is denied Google’s tag can still send cookieless measurement pings; elsewhere they are on by default and you can turn them off in Cookie Settings (see our Privacy Policy). If you click “Use this number in a free invoice”, the first ID travels in that page’s web address (?number=…), so it reaches us and Google Analytics as part of that page address.