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TapTax
Invoice numbering

Number your
invoices right

Build a numbering format, list your next invoice numbers, or find the number after the last one you sent.

Your first invoice number

INV-0001

Then INV-0002, INV-0003 and so on: one sequence, never reused.

Optional. Your initials or business name make numbers easy to recognise, for example AB or SMITH.

Separator
Date in the number

A year shows at a glance when an invoice was raised. The count carries on across years unless you choose to restart it.

4 digits gives 0001 to 9999; the number keeps growing past that rather than wrapping.

Next 10 numbers
  1. INV-0001
  2. INV-0002
  3. INV-0003
  4. INV-0004
  5. INV-0005
  6. INV-0006
  7. INV-0007
  8. INV-0008
  9. INV-0009
  10. INV-0010

Already invoicing? Find your next number

Any format. The last run of digits counts up by one and keeps its zeros.

Your next invoice number

INV-0042

Never reuse or skip a number. If you cancel an invoice, keep its number and issue a credit note, so the sequence stays complete.

Put this calculator on your site

Free to embed on any website or blog. It needs no script, sets no cookies and works in any page builder that accepts an iframe.

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<iframe
  src="https://taptax.co.uk/invoice-number-generator/embed"
  title="Invoice number generator"
  width="100%"
  height="600"
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></iframe>
<p style="font-size:12px">
  <a href="https://taptax.co.uk/invoice-number-generator">Invoice number generator by TapTax</a>
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Unique
every invoice needs its own identifying number
Sequential
a VAT invoice number must follow on from the last
Any format
letters, dates and numbers are all allowed
Invoice number
The unique reference that identifies one invoice. GOV.UK lists it first among the details every invoice must include, and for a VAT invoice it must be part of a sequence that uniquely identifies the document.

What the rules say

Every invoice needs a unique identification number. A VAT invoice needs a sequential number, based on one or more series, that uniquely identifies it. Nothing prescribes the format, so a plain count, a prefix, your initials or a date part all work, as long as no number is ever used twice and each sequence only goes up.

More than one series is allowed, for example one per shop or one per year, provided each is sequential and a number cannot appear in two of them.

Common formats

FormatExampleGood for
Plain sequence0042Simplest. Fine for a small business with one sequence.
Prefix and sequenceINV-0042Tells an invoice apart from a quote or credit note at a glance.
Initials and sequenceJS-042Useful when customers receive invoices from several suppliers.
Year and sequenceINV-2026-0042Shows the year an invoice was raised. Many restart the count each year.
Year, month and sequence202604/042Easy to file by month, if you invoice often.

Mistakes to avoid

  • Reusing a number.Two invoices with one number confuse your records and your customer’s, and break the sequence HMRC expects.
  • Deleting a mistake. Keep the wrong invoice and its number, and cancel it with a credit note, so the sequence has no gap to explain.
  • Starting at 0001 to look established. You can start anywhere, and many businesses start at 100 or 1000. Just keep counting up from there.
  • Too few digits. A number that outgrows its padding still works, but 0999 followed by 1000 sorts oddly in a spreadsheet. Allow room for growth.
Key takeaways
  • Every invoice needs a unique number; a VAT invoice needs one from a sequence.
  • Any format works: a prefix, your initials or the year are all fine.
  • Never reuse or delete a number: cancel a wrong invoice with a credit note.
  • Use one sequence, or several that can never overlap.

Setting the due date too?

The due date on each invoice follows from your payment terms; the invoice due date calculator works it out.

  • Invoice due date

    When an invoice is due under its payment terms, and when interest can start.

  • Late payment interest

    The statutory interest and fixed compensation you can add to a late business invoice.

  • VAT

    Add VAT to a price or take it out, at 20, 5 or 0 percent.

  • Reverse charge checker

    Whether the VAT domestic reverse charge applies to a construction invoice.

Frequently asked questions

What should my first invoice number be?

Anything you like, as long as every later number follows on from it. INV-0001 is common; starting at 100 or 1000 is fine too.

Do invoice numbers have to be sequential?

Every invoice needs a unique number, and a VAT invoice needs a sequential number from one or more series that uniquely identifies it. Numbering every invoice in sequence is the simple way to meet both.

Can I put letters or the year in an invoice number?

Yes. A prefix, your initials or a date part are all allowed. What matters is that each number is used only once and each series only counts upwards.

What if I make a mistake on an invoice?

Keep the invoice and its number and issue a credit note to cancel or correct it, then raise a new invoice with the next number. Deleting it leaves a gap in the sequence.

Can I restart numbering each year?

Yes, if the year is part of the number, so 2027-0001 can never be confused with 2026-0001. Restarting a plain sequence would repeat numbers.

Numbered, sent and tracked.

TapTax creates and sends your invoices, tracks which ones are paid and files your quarterly updates to HMRC. Start on the free plan, no card needed.

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Where these figures come from

Rates from GOV.UK.