How to Invoice a Client as a Freelancer (UK)

When to Send Invoices

Timing is crucial when it comes to invoicing. Send your invoice too early, and you might seem presumptuous; leave it too late, and your payment gets pushed back even further. As a UK freelancer, understanding when to invoice can significantly impact your cash flow.

Upon project completion is the most common approach. Once you've delivered the final work and received client approval, send your invoice immediately. The work is fresh in everyone's mind, and clients are typically most receptive to paying straight after delivery.

For larger projects, consider milestone billing. Breaking a £5,000 project into three invoices of £1,500, £2,000, and £1,500 tied to specific deliverables helps manage your cash flow and reduces risk on both sides.

Retainer work should be invoiced consistently — either at the start of each month (payment in advance) or at the end (payment in arrears). Whichever you choose, stick to the same date each month so clients can plan for it.

What to Include on an Invoice

A UK invoice must contain specific information to be legally valid and to ensure you get paid without delays. Here's what every invoice needs:

Your business details:

• Your business name or your name as a sole trader
• Your business address
• Your contact details (email and phone)
• Your VAT number (if VAT registered)

Client details:

• Client's business name or individual name
• Client's address
• Contact person (helpful for larger organisations)

Invoice specifics:

• Unique invoice number (e.g., INV-2026-001)
• Invoice date
• Due date (based on your payment terms)
• Clear description of services provided
• Quantity or hours (where applicable)
• Unit price and total for each line item
• Subtotal, VAT amount (if applicable), and grand total

Payment information:

• Bank name and sort code
• Account number
• Payment reference (usually the invoice number)
• Alternative payment methods accepted

Step-by-Step Creation Process

Creating a professional invoice doesn't need to be complicated. Follow this straightforward process:

Step 1: Gather your information
Before you start, collect the client's correct business name, billing address, and any purchase order number they've provided. Getting these details wrong is a common cause of payment delays.

Step 2: Choose your invoice number
Use a consistent numbering system. Many freelancers use the format YEAR-NUMBER (e.g., 2026-001) or CLIENT-YEAR-NUMBER. Whatever system you choose, make sure each number is unique.

Step 3: List your services clearly
Be specific about what you're billing for. Instead of "Design work - £800", write "Homepage redesign including responsive layouts, hero section animation, and three revision rounds - £800". Clear descriptions reduce queries and speed up approval.

Step 4: Calculate totals correctly
Double-check your maths. If you're VAT registered, clearly show the net amount, VAT amount (at 20%), and gross total. If you're not VAT registered, you can include a simple statement: "Not VAT registered".

Step 5: Review before sending
Check spelling of names, verify amounts match your quote or agreement, and ensure your bank details are correct. A two-minute review can save weeks of chasing later.

How to Send Invoices

How you send your invoice can impact how quickly you get paid. Here are your main options:

Email attachment (PDF)
The most common method. Always send your invoice as a PDF rather than a Word document — PDFs can't be accidentally edited and look more professional. Include a brief, friendly email message referencing the project.

Online invoicing software
Tools like FreelancerHub let you send invoices directly, track when they're viewed, and accept online payments. This is the fastest route to getting paid and removes the need for manual follow-up.

Client portals
Some larger clients have their own systems where you'll need to submit invoices. Ask about this during onboarding to avoid delays.

Following Up on Invoices

Even with the best invoicing practices, you'll occasionally need to follow up. Here's a sensible timeline:

Day 1: Send the invoice with a clear due date.

3 days before due date: Send a friendly reminder if payment hasn't been received.

Due date: If unpaid, send a polite reminder that payment is now due.

7 days overdue: Send a firmer follow-up requesting immediate payment.

14+ days overdue: Consider a phone call and mention potential late payment interest.

Keep all communication professional and factual. Most late payments are due to oversight rather than unwillingness to pay.

Common Mistakes to Avoid

Even experienced freelancers make invoicing errors. Here are the most common pitfalls:

• Vague descriptions — "Consulting" or "Work done in January" invites queries. Be specific.
• Wrong client details — Misspelling a company name or using an outdated address causes delays.
• Missing purchase order numbers — Many corporate clients won't process invoices without their PO reference.
• Unclear payment terms — "Due soon" means nothing. Use specific dates or terms like "Net 14".
• Forgetting to invoice — Track your unbilled work religiously. Invoicing software helps with this.
• Inconsistent branding — A professional, branded invoice builds confidence. A plain text email does not.

Invoice Checklist

Before sending any invoice, run through this checklist:

Mastering invoicing takes practice, but once you establish good habits, it becomes second nature. The key is consistency — same format, same process, same timing. Your clients will appreciate the professionalism, and you'll enjoy faster payments.