How to Write an Invoice — The Complete Guide

What is an invoice?

An invoice is a formal document a seller sends to a buyer requesting payment for goods or services. It's a legal record of what was sold, how much it costs, and when payment is due. Invoices are essential for getting paid on time and keeping clean financial records — required for both tax purposes and accounting.

An invoice is different from a receipt (proves payment has been made), a quote (estimate before work begins), or a purchase order (request from buyer to seller).

What to include on an invoice

A professional invoice has 8 essential elements. Skip any of these and you risk delays, disputes, or simply not getting paid:

1. The word "Invoice" — clearly marked at the top so it's not mistaken for a quote.
2. Your business details — name, address, email, phone, and any tax ID (VAT, EIN, etc).
3. A unique invoice number — sequential like INV-001, INV-002. Never reuse a number.
4. Issue date — the day you send the invoice.
5. Client details — their full name (or company), address, and contact email.
6. Itemized list — each line shows description, quantity, unit price, and line total.
7. Subtotal, tax, and total — broken down clearly. Plus the currency.
8. Payment instructions — bank account, PayPal, Stripe link — wherever you want money sent.

A real invoice example

Here's what a properly structured invoice looks like:

Want to make one like this? Try our free invoice generator — fill in the form, download the PDF in 30 seconds.

Payment terms (Net 30, Net 15, etc)

"Net X" means payment is due X days after the invoice date. The most common terms are:

For most freelancers, Net 15 or Net 30 is the sweet spot — long enough that clients have time to pay, short enough that you don't wait forever for cash.

Tax, VAT, and sales tax

Tax rules depend on where you are and what you sell:

United Kingdom

If you're VAT-registered (currently required above £90,000/year turnover), you must charge 20% VAT on most goods and services. Show VAT separately on the invoice and include your VAT number.

European Union

VAT rates vary by country (19% in Germany, 21% in Spain, 25% in Sweden). For B2B sales between EU member states, the reverse charge rule often applies — you don't charge VAT, the buyer accounts for it.

United States

No federal VAT. Sales tax is charged at the state level (and sometimes city/county). Typically only required on physical goods, not services.

Morocco / North Africa

Morocco's TVA is 20% standard rate. Required if you're registered. Include your ICE and IF on B2B invoices.

How to send an invoice

Methods ranked by how fast they get paid:

1. PDF emailed with a Pay Now link — fastest. Client clicks, pays by card, you get notified instantly.
2. PDF emailed manually — works fine with clear bank/PayPal details on the invoice.
3. Through an accounting tool — Xero, QuickBooks, FreshBooks send invoices with payment integration.
4. Printed and mailed — only for old-school enterprise clients. Slow.

Always send a quick reminder 3 days before the due date. Most "late" payments aren't malicious — clients just forget.

How to chase late payments

The single biggest cause of cash flow problems for freelancers. Here's a proven follow-up sequence:

Day 1 after due date — Friendly reminder

Subject: Quick reminder: Invoice INV-001 is due

Keep it light. "Hi {name}, just a friendly reminder that invoice INV-001 was due yesterday. Could you confirm when payment will be made? Thanks!"

Day 7 — Firmer follow-up

Subject: Invoice INV-001 — 7 days overdue

Request a specific date. "Hi {name}, invoice INV-001 is now 7 days overdue. Please let me know when I can expect payment, or if there's an issue with the invoice."

Day 14 — Final notice

Subject: Final notice: Invoice INV-001 — please respond

Mention next steps. "Invoice INV-001 is now 14 days overdue. If payment is not received within 7 days, I will need to add a late fee and pause any ongoing work."

Day 30+ — Escalate

Options: small claims court, debt collection agency, or a Letter Before Action (UK) / Demand Letter (US). Most clients pay before this stage if you've followed up consistently.

Charging late fees

Late fees are legal — but only if:

• You stated them in advance (in your contract or on the original invoice)
• The amount is reasonable (not punitive)
• You give the client a chance to pay before applying the fee

Common structures:

• Percentage — 1.5% of unpaid balance per month is standard.
• Flat fee — $25–$50 per missed deadline.
• Statutory interest (UK) — for B2B sales, charge 8% above Bank of England base rate under the Late Payment Act, plus £40–£100 fixed compensation.

Pro tips to get paid faster

1. Send the invoice the day work is completed — not at month-end.
2. Make it easy to pay — Pay Now button via Stripe, not just bank details.
3. Set short payment terms — Net 15 instead of Net 30 unless required otherwise.
4. Send a reminder 3 days before the due date — heads off most late payments.
5. Use professional templates — sloppy invoices get pushed to the bottom of the AP team's pile.
6. Track everything — know who owes what and when.
7. Confirm receipt — ask the client to confirm. Removes the "I never got it" excuse.

Frequently asked questions

Do I need to be a registered business to send invoices?

No. Sole traders and freelancers can send invoices using their personal name and address. Once you scale up, registering as a sole trader / LLC / Ltd makes things cleaner for tax.

Can I send an invoice without VAT?

Yes — if you're not VAT-registered. Just don't include "VAT" or any VAT number on the invoice.

What if a client refuses to pay?

Try to resolve it directly first. If that fails, options include small claims court, a debt collection agency, or simply writing it off and never working with them again.

How long should I keep invoice records?

Most countries require keeping invoices: 6 years in the UK, 3 years federal in the US, 10 years in many EU countries. Keep PDFs backed up in cloud storage.