US reader note. This page uses US English but discusses UK tax, VAT, CIS, or payment rules. Treat it as UK-focused educational content, not US legal, tax, or accounting advice. US requirements vary by federal, state, and local rules, so check with a qualified professional before applying anything to a US business.

What is an invoice?

An invoice is a formal request for payment. It tells your customer exactly what work you did, how much they owe, and how to pay you. For sole traders in the UK, invoicing is not just good practice -- it is how you get paid on time and keep clean records for your Self Assessment tax return.

You do not need special software or a qualification to send a valid invoice. You need the right details in the right place, and you need to send it promptly.

What must be on a sole trader invoice?

HMRC does not prescribe a rigid invoice template for non-VAT-registered sole traders, but there are details you should always include to avoid disputes and make sure your invoice holds up if you ever need to follow up on payment formally.

Every invoice you send should contain:

  • Your name or business name -- the trading name you use with customers.
  • Your address -- your business address or registered correspondence address.
  • A unique invoice number -- sequential numbers work well. Something like INV-001, INV-002, and so on. Each number must be different.
  • The invoice date -- the date you issue the invoice, not necessarily the date you did the work.
  • Customer name and address -- who you are billing and where they are based.
  • A clear description of the work -- what you did, where you did it, and any reference numbers the customer might need.
  • The amount due -- the total the customer needs to pay. If you break it down by line items, show a total at the bottom.
  • Payment terms -- when the invoice is due. For example, "due within 14 days of invoice date."
  • Your bank details -- routing and account details, or the payment instructions you use so the customer can pay by bank transfer or ACH.
VAT-registered? If you are registered for VAT, your invoice must also include your VAT registration number, the VAT rate applied, the VAT amount, and the gross total. The rules for VAT invoices are stricter. Check the HMRC guidance on VAT invoicing if this applies to you.

When to send the invoice

Send your invoice as soon as the work is finished. The same day if you can. The longer you wait, the less urgency the customer feels, and the easier it is for the job to slip down their list of things to pay.

Contractors who invoice on the day they finish a job consistently get paid faster than those who wait until the weekend or the end of the month to sort through their paperwork. It does not need to be complicated. A clear invoice sent within hours of completing the work sets the right tone.

If you are working on a larger project with staged payments, agree the milestones and invoice dates before you start. That way, neither you nor the customer is surprised when the invoice arrives.

Payment terms

Payment terms tell the customer how long they have to pay. Common terms for contractors in the UK include:

  • 7 days -- often used for small residential jobs. Gets money in quickly.
  • 14 days -- a reasonable middle ground that most residential customers are comfortable with.
  • 30 days -- standard for commercial clients, landlords, and letting agents. Some larger companies will expect this.

For residential customers, shorter payment terms are generally better. Most homeowners are happy to pay within a week or two. For business-to-business work, 30 days is often expected and may even be written into a contract.

Whatever you choose, state the terms clearly on the invoice. Do not leave it ambiguous. Something like "Payment due within 14 days of invoice date" is clear and professional.

What if they do not pay?

Late payment happens. It does not always mean the customer is trying to avoid paying -- sometimes they forget, or the email went to spam, or they are waiting for their own client to pay them first. A structured follow-up process helps you stay on top of it without damaging the relationship.

A sensible timeline looks like this:

  • Day 7 after due date -- send a polite reminder. Keep it friendly. A short email referencing the invoice number and amount is enough.
  • Day 14 -- follow up again, slightly firmer. Mention that the payment is now overdue and ask if there is an issue.
  • Day 28 -- send a formal overdue notice. State the amount, the original due date, and that you expect payment within a set number of days.
  • Day 30 and beyond -- if you have had no response, you may need to consider a letter before action. This is a formal letter giving the debtor 14 days to pay before you take the matter to court.

For debts under 10,000 pounds, the small claims court (Money Claims Online) is a straightforward process that does not require a lawyer. For larger amounts or more complex situations, it may be worth getting legal advice.

Important. This article is general information, not legal advice. For specific situations involving disputed invoices, contracts, or debt recovery, speak to a lawyer or contact Citizens Advice.

A faster way to handle invoicing

Writing invoices, remembering to chase, and keeping track of who has paid is a drag -- especially when you are busy with actual work. That is the problem WOPA was built to solve.

With WOPA, you send a WhatsApp message describing the job, the customer, and the amount. WOPA drafts the invoice with all the right details, asks you to confirm, and then emails a PDF to your customer. Reminders are sent automatically at 7, 14, and 28 days. When the customer pays, you tell WOPA and the reminders stop.

No app to download. No spreadsheet to maintain. Just WhatsApp.

Join the waitlist to get US beta access when WOPA launches.