How to create an invoice? The ultimate guide for freelancers

You've closed the client, completed the task, and now it's time for the most fun part of being self-employed: Getting paid for your work.

But how do you actually create an invoice that looks professional and complies with all strict legal requirements?

Many new freelancers, developers, and consultants fall into the first major trap: They google for a free Word template. It might work the first time, but it costs you hours in administration and increases the risk of errors, which ultimately means the client might not pay you on time.

In this guide, we review exactly what a valid invoice must contain, what mistakes you absolutely must avoid, and how to build a professional image from day one.

What must an invoice contain? (The 9 legal requirements)

According to bookkeeping and VAT laws, there are specific requirements for the content of your invoice. If just one of these is missing, your client – especially if it's a larger company (B2B) – can refuse to pay it until you've sent a new one.

Here is your checklist. Your invoice must contain:

1. Invoice number: Must be sequential (e.g., 1, 2, 3 or 1001, 1002). You cannot skip numbers.
2. Invoice date: The day you issue the invoice.
3. Seller's information: Your name/company name, address, and VAT/company registration number.
4. Buyer's information: The client's name, address, and their registration number if it's a company.
5. Delivery date: The date the goods or services were delivered (if different from the invoice date).
6. Description of the service: What did the client buy? Be specific (e.g., "Web development: Landing page setup, 10 hours").
7. Price per unit: The price excluding VAT for each line.
8. VAT: The applicable VAT rate and the total VAT amount.
9. Total amount: The full amount the client must pay, including VAT.

Remember the payment details! It's not a direct legal requirement from the tax authorities, but it is quite essential for you to get your money: Remember to include your bank registration and account number as well as your payment terms (e.g., "Net 14 days").

Word and Excel are a trap for modern independents

When you google "how to make an invoice", you will find thousands of free Excel and Word templates.

Don't do it.

As a modern freelancer or "vibe coder", you build digital, scalable solutions. Why manage your own business with outdated, manual files?

When you use Word, you have to remember the invoice number yourself (remember the rule about sequential numbers!). You have to calculate the VAT yourself without making typing errors, and you have to save every single invoice as a PDF in neat folders for your accounting.

What happens if you use the same invoice number twice? Then you have a problem with the tax authorities.
What if you forget to save a copy? Then you have a problem with the bookkeeping act.

How to create an invoice in 1 minute (Without admin hassle)

Why spend time on manual templates or pay expensive percentages to umbrella organizations to "handle it for you", when good software does it all automatically?

With a system like Fakturify, you can send your first invoice in under a minute.

1. Sign up for free: You enter your company details once.
2. Create the client: Enter the client's name or company number, and the system automatically fetches the address details.
3. Add your service: Write what you've done and specify the price.
4. Approve and send: Fakturify calculates the VAT, generates a unique sequential invoice number, sets it all up in a razor-sharp, professional design, and sends it directly to the client's inbox.

You appear highly professional, you comply with legislation, and the system automatically saves a copy so your accounting always adds up.

Typical mistakes that delay your payment

Even experienced consultants and designers make mistakes. Here are the three biggest you must avoid:

• Too vague description: If it just says "Consulting", you risk the client's accounting department rejecting it and asking for a specification. Write exactly which project it concerns.
• Wrong reference: Large companies often require a "PO code" (Purchase Order) or the name of a specific contact person to be able to pay. Make sure to get this information before invoicing.
• Short payment deadlines without agreement: Do you write "Net 8 days", but the client has a standard policy of current month + 30 days? Align expectations beforehand.

How do you send the invoice to the client?

For B2B and B2C (companies and private individuals), a PDF attached to an email is the standard. Remember to write a short, polite message in the email itself: "Hi [Name], Thank you for a good collaboration. Attached you will find the invoice for [Task]."

Are you invoicing a public authority (municipality, state, region)? Then a PDF is not enough. Here, it is mandatory to send an electronic invoice via the EAN/Peppol system (OIOUBL format in Denmark).

With an invoicing program like Fakturify, you simply enter the client's EAN number, and the system handles the formatting and dispatch for you in the background.

FAQ: Frequently asked questions about invoicing

Can you make an invoice as a private person without a registered company?
Yes (in many jurisdictions like Denmark, using your CPR number), as long as you turnover less than a certain threshold (e.g., 50,000 DKK in a 12-month period). Note that you MUST NOT add VAT to the invoice without a company registration, and you must report the amount as B-income to the tax authorities yourself.

What does it cost to use an invoicing program?
Many think it's expensive to use professional software. At Fakturify, you can actually start completely free. You save hours on administration and avoid expensive mistakes.

What do I do if I made a mistake on a sent invoice?
You cannot simply delete the invoice (due to the requirement for sequential numbers). Instead, you must issue a credit note that cancels the old invoice, and then send a completely new, correct invoice.