Invoice Number Generator
Generate a batch of sequential invoice numbers with your chosen prefix and format. Copy them into your spreadsheet, accounting software, or save them for reference — completely free.
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Frequently asked questions
Do invoice numbers have to be sequential?
HMRC requires that VAT invoices have a unique sequential number. The numbers do not need to be perfectly consecutive (gaps are acceptable) but they must be in sequential order and each number must be unique. Using a consistent numbering system such as INV-0001, INV-0002 makes it easy to identify missing numbers and maintain proper records.
What format should invoice numbers use?
There is no single required format. Common approaches include a simple prefix and sequence (INV-001), a year and sequence (INV-2025-001), or a full date and sequence (INV-20250305-001). Including the year or date in the number makes it easy to find invoices when you have been trading for several years. Use zero-padding (e.g. 001 not 1) so numbers sort correctly in spreadsheets.
Can I reuse invoice numbers?
No. Every invoice must have a unique number. Reusing numbers could create confusion, errors in your accounts, and problems with HMRC if you are VAT-registered. If you need to cancel an invoice, void it rather than reusing its number.
What prefix should I use for my invoice numbers?
Any short, consistent prefix works. Common choices are "INV" (invoice), your business initials, or a project code if you invoice multiple projects separately. Keep it short — 3 to 5 characters — so invoice numbers are not unwieldy.
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Never worry about invoice numbers again
InvoiceAdept automatically assigns the next sequential invoice number every time you create an invoice — no spreadsheets, no duplicates.
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