Every UK invoice needs a unique number, your details and your customer's, a description, the supply date, the invoice date and the amount owed, and VAT-registered businesses need a fuller VAT invoice. Whether you're paid on time depends mostly on what happens after that: who receives the invoice, how easy it is to pay, how consistently it's followed up and how cleanly the payment is matched back.
In this article
The short version
- Every UK invoice needs a unique number, both parties' details, a description, the supply date, the invoice date and the total.
- VAT-registered businesses invoicing each other need a VAT invoice, normally within 30 days of the supply.
- Getting paid depends on reaching someone who can approve the invoice and giving them an easy way to pay.
- On business invoices you can charge statutory interest at 8% above base rate plus £40 to £100 compensation.
- From April 2029, VAT invoices will have to be issued as e-invoices.
What a UK invoice must include
Whether or not you're VAT registered, every invoice you send needs:
- a unique identification number
- your business name, address and contact details
- your customer's name and address
- a clear description of what you're charging for
- the supply date, meaning when you provided the goods or did the work
- the invoice date
- the amount or amounts charged
- the VAT amount, if VAT applies
- the total owed
The supply date and the invoice date are separate fields, and you need both on the invoice even if you aren't VAT registered.
Your business structure adds a little more, and so does VAT:
| If you're | You also need |
|---|---|
| A sole trader | Your own name and any business name you trade under, plus an address where legal documents can reach you if you use a business name |
| A limited company | The full company name exactly as it appears on your certificate of incorporation, and the names of all your directors if you choose to name any of them |
| VAT registered and invoicing another VAT-registered business | A VAT invoice, which adds your VAT number, the time of supply, the VAT rate and net amount for each line and the total VAT in sterling, normally issued within 30 days of the supply |
For VAT invoices of £250 or less including VAT, HMRC lets you issue a simplified invoice with fewer details, as long as nothing on it is exempt.
Invoice numbers can follow any scheme you like, as long as no number is ever used twice. VAT invoices need a sequential number from one or more series, so a separate series for each brand or company is fine. A count that starts again for every new client puts duplicate numbers in your ledger and makes payments harder to match later.
You don't need a particular format today, so a PDF or an invoice from your accounting software is valid. That's due to change for VAT invoices: the government has said that from April 2029 they'll have to be issued as e-invoices, meaning structured data that another system can read without anyone retyping it.
How to get an invoice paid once it's sent
Payment terms are easiest to enforce when they're agreed before the work starts and written on the invoice as a date. If you never agreed terms with a business customer, the law gives them 30 days, counted from the later of the day you did the work and the day they were told the amount. So an invoice raised two weeks after the job finishes pushes your own due date back by two weeks.
Next, get it in front of someone who can approve it. Larger customers often pay through a shared inbox and a weekly or monthly payment run, and they're unlikely to pay an invoice that doesn't quote the purchase order number or reference they gave you. Ask who approves invoices when you take on the work, not after an invoice has gone overdue.
Then make paying easy. An invoice that asks your customer to open their banking app, add you as a payee and type a reference is asking them to do a small job, and that's easy to put off. A payment link on the invoice lets them pay by card, Apple Pay, Google Pay or pay by bank in a few taps, with the reference filled in for them. For work you bill every month, a direct debit mandate collects on the due date without anyone having to decide to pay.
If you'd rather not run several tools for this, Adfin sends each invoice with a payment link by email, SMS or WhatsApp, and your customer can pay by card, Apple Pay, Google Pay, pay by bank or bank transfer from the same page. Customers who've signed a direct debit mandate are collected on the due date instead.
What to do when an invoice goes overdue
Chasing late payers can take up a surprising amount of time. Government-commissioned research published in 2025 found that businesses chasing late payments spend an average of 86 hours a year on it.
A short, consistent sequence tends to work better than an occasional stern email: a friendly reminder a few days before the due date, another on the day, then follow-ups at set intervals with the payment link in every message. A phone call or a formal letter can wait until the gentler steps have run.
For business customers, the law also lets you charge for lateness, whether or not your contract mentions it:
- interest at 8% above the Bank of England base rate, which is 11.75% a year while the base rate is 3.75%
- fixed compensation of £40 on invoices under £1,000, £70 from £1,000 to £9,999.99 and £100 on £10,000 or more
These rights cover business-to-business invoices only, not consumers, and a contract can replace them with its own remedy if that remedy is substantial. Few businesses use them, partly because working out the interest and raising a second invoice by hand is tedious.
That's admin that software can take off your hands. Adfin's collection agents chase overdue invoices on the schedule you set, over email, SMS and WhatsApp from your own email domain, and can add statutory interest and compensation to overdue business invoices, with grace periods and waivers for the customers you'd rather not charge.
How payments get matched back to invoices
An invoice isn't finished until the payment is matched to it in your books, and that step tends to break in the same few ways:
- the reference is missing or mistyped
- the customer pays part of the invoice, or slightly too much
- one transfer covers several invoices
- your payment provider deducts its fees before paying you, so the amount in the bank never equals the invoice
The last one costs the most time, because every payout has to be split into invoice value and fees, usually through a clearing account, with the VAT on the fees handled separately. Being paid in full, with fees invoiced to you separately, removes that work.
Corrections need care too. If an invoice turns out to be wrong after it's gone out, issue a credit note against it and a fresh invoice, and keep both. Editing or deleting the original leaves you and your customer holding different versions of the same document.
Adfin matches payments to invoices automatically, including part payments and payments with missing references, and syncs both ways with Xero and QuickBooks. It pays out every weekday with nothing deducted and invoices its own fee separately, so each payout adds up to the full value of the payments in it.
Common questions
What must a UK invoice legally include? A unique number, your business name, address and contact details, the customer's name and address, a description, the supply date, the invoice date, the amounts charged, any VAT and the total owed. Sole traders, limited companies and VAT-registered businesses each add a few details.
Do invoice numbers have to be sequential? VAT invoices need a sequential number from one or more series. For other invoices the number just has to be unique, though one continuous sequence makes it easiest to keep that way.
How long do I have to issue a VAT invoice? Normally within 30 days of the date of supply. You only have to issue one when you and your customer are both VAT registered.
Can I send invoices if I'm not VAT registered? Yes. Send a standard invoice with the required details and no VAT, and don't charge or show VAT until you're registered.
Is a PDF invoice still valid? Yes, for now. The government has said VAT invoices will have to be issued as structured e-invoices from April 2029, and a PDF isn't an e-invoice in that sense.
How long does a business customer have to pay? As long as you agreed. If you agreed nothing, 30 days from the later of the day you did the work and the day they were told the amount owed.
Sources
- GOV.UK - Invoicing and taking payment from customers: invoices, what they must include (accurate as of October 2026) https://www.gov.uk/invoicing-and-taking-payment-from-customers/invoices-what-they-must-include
- HMRC - Record keeping (VAT Notice 700/21) (accurate as of October 2026) https://www.gov.uk/guidance/record-keeping-for-vat-notice-70021
- GOV.UK - Late commercial payments: charging interest on commercial debt (accurate as of October 2026) https://www.gov.uk/late-commercial-payments-interest-debt-recovery/charging-interest-commercial-debt
- Department for Business and Trade - Late payments research: impact on the UK economy (accurate as of October 2026) https://assets.publishing.service.gov.uk/media/688a089a6478525675738ff9/late_payments_research_impact_on_uk_economy.pdf
- HM Treasury - Budget 2025 (accurate as of October 2026) https://www.gov.uk/government/publications/budget-2025-document/budget-2025-html
- Adfin - Pricing (accurate as of October 2026) https://www.adfin.com/pricing
