Invoicing looks simple, and then a client pays three weeks late, an invoice has the wrong details or a VAT question appears. This guide is a complete walk-through for UK freelancers: what an invoice is, what goes on it, how to send and track it, what to do about late payment, and how long to keep your records. It is general information, not legal or tax advice.
What an invoice does
An invoice is a request for payment, and it is also your record of a sale. It tells your client what they owe and why, and it tells HMRC how much you earned. Every invoice you issue counts towards your income, so a clear invoicing process makes your tax return easier too.
What to include
- The word “Invoice”, a unique invoice number and the invoice date.
- Your name or business name, address and contact details.
- Your client’s name and address.
- A clear description of what you supplied, with quantities, rates and the period covered.
- The total due, with any discounts.
- The payment terms, due date and your bank details.
- Your VAT number and the VAT on each item, if you are VAT registered.
Our shorter guide, how to write an invoice as a freelancer, goes through each item. You can also create one in minutes with our free invoice generator.
Numbering your invoices
Use a simple, sequential number, for example 1001, 1002, 1003. Never reuse a number and avoid gaps, because gaps raise questions in an HMRC check. If you want to show the year, a format like 2026-001 works well.
VAT on invoices
Only charge VAT if you are registered. If you are, a VAT invoice must show your VAT number, the rate for each line, the VAT amount and the total including VAT. If you are close to the registration threshold, read our guide to VAT registration.
Choose sensible payment terms
Common terms are 7, 14 or 30 days. Shorter terms improve your cash flow, and large clients often insist on 30 days or more. Write the actual due date on the invoice, not just “30 days”, and agree the terms in your quote or contract before work starts.
Sending your invoice
Send a PDF by email to the person who approves payment, not just to your day-to-day contact. Use a clear subject line such as “Invoice 1042 from Jane Smith, due 14 November”. If the client uses a purchase order number, quote it on the invoice, since many finance teams reject invoices without one.
Track what is owed
Keep a list of every unpaid invoice with its due date. An ageing view groups unpaid invoices by how overdue they are, so you can see at a glance who to chase. Check it weekly.
Chasing late payments
- The day before it falls due: a short, friendly reminder.
- On the due date or a few days after: a polite email asking when payment will arrive.
- One to two weeks late: a firm email that states the amount, the due date and your payment terms.
- Still unpaid: a formal letter that mentions your right to statutory interest and compensation, and gives a final date.
Under the Late Payment of Commercial Debts legislation, businesses can charge interest on late business-to-business payments at 8% above the Bank of England base rate, plus fixed compensation of £40 for debts under £1,000, £70 for £1,000 to £9,999.99 and £100 for £10,000 or more. For more ideas, see nine ways to get paid faster.
Fixing mistakes with credit notes
Never delete or edit an issued invoice. Issue a credit note that cancels the original and raise a corrected invoice. Your records stay in order and the audit trail is clear.
Record keeping
Keep copies of every invoice you issue and receive. For Self Assessment, HMRC expects you to keep records for at least five years after the 31 January filing deadline for that tax year. VAT records generally need to be kept for six years. Store invoices digitally and attach them to the related transactions.
Common invoicing mistakes
- Missing or duplicate invoice numbers.
- Vague descriptions that invite questions.
- No due date, or terms that were never agreed.
- Sending to the wrong person.
- Forgetting to follow up until months later.
- Charging VAT when you are not registered.
How AvrioBooks helps
Create an invoice from your products or services, and AvrioBooks numbers and totals it for you. Download it as a PDF or email it to the client, record payments when they arrive and issue credit notes when you need to correct something. The aged receivables report shows what is overdue. See AvrioBooks for freelancers and the help guide Delete or correct an invoice.
Frequently asked questions
What must a UK freelance invoice include?
A unique invoice number, the date, your details, your client's details, a description of the work, the amount due, payment terms and your bank details. VAT-registered businesses must also show their VAT number and the VAT charged.
How long should I keep invoices?
For Self Assessment, at least five years after the 31 January filing deadline for that tax year. VAT records generally need to be kept for six years.
Can I charge interest on a late invoice?
For business-to-business debts you can claim statutory interest at 8% above the Bank of England base rate, plus fixed compensation of £40, £70 or £100 depending on the amount.
What should I do if I make a mistake on an invoice?
Issue a credit note to cancel it and raise a new, correct invoice. Do not delete or edit the original.
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