When you’re operating across borders, value-added tax (VAT) numbers are one way your business proves it’s doing so legally. These identifiers show that you’re charging the right tax, applying the right exemptions, and protecting the business if something goes wrong. The Netherlands, for example, allows reverse-charge VAT for cross-border transactions if the customer has a VAT number. Sometimes, however, VAT numbers can be wrong: they can be faked, mistyped, or misused. And if you don’t catch a mistake early, your compliance might be at risk.

Below, we’ll explain how to check a VAT number (btw nummer controleren), what can go wrong if you don’t, and how to build validation into your operations in a flexible, audit-ready way.

What’s in this article?

• What is a VAT number, and why do businesses need it?
  
• Why is it important to check VAT numbers?
  
• How do you check a Dutch VAT number?
  
• How do you use the EU VIES system for VAT validation?
  
• What happens if a VAT number is invalid?
  
• How often should businesses verify VAT numbers?
  
• What tools can automate VAT number checks?
  
• How Stripe Invoicing can help
  

What is a VAT number, and why do businesses need it?

A VAT number is a government-issued ID that tells the world your business is registered to collect VAT. A VAT ID is required in the EU if you sell goods or services that are subject to VAT. It also signals to your customers, partners, and tax authorities that you’re officially in the VAT system and following the rules.

Every EU country formats VAT numbers differently, but they follow the same basic pattern: a two-letter country code, followed by a unique string of numbers (and sometimes letters). In the Netherlands, for example, the VAT ID, called a btw-identificatienummer, looks like this: NL123456789B01. That’s different from the RSIN, which is how government systems link your business across databases, so it’s important to keep these numbers straight.

Why does this number matter? If you’re VAT-registered, you can charge VAT on sales, reclaim VAT on business expenses, and apply 0% VAT on eligible cross-border B2B sales.

Without a VAT number, you’re either charging VAT illegally, not charging VAT you should be, missing out on deductions, or limiting your ability to sell cross-border. It’s a key part of doing business in the EU legally and efficiently.

Why is it important to check VAT numbers?

Whenever you collect a customer’s VAT number, you must check that it’s valid. Every time you zero-rate a B2B sale in the EU, you’re relying on the customer’s VAT number being active and registered for cross-border trade. If it’s not, you’ll have to deal with the consequences.

If you work with invalid VAT numbers, you’re facing significant risks.

You can’t zero-rate without a valid VAT number

A valid customer VAT number is required when applying 0% VAT on cross-border sales of goods within the EU. If you don’t have a valid number, you must charge VAT.

If you skip verification and the number is invalid, auditors can reclassify the sale, and you might be liable for the uncollected tax plus interest or penalties.

It protects you from errors and fraud

Typos happen. Transposed digits or the wrong country code can make a real VAT number look invalid, but a quick check catches this early. Additionally, fake VAT numbers exist. Fraudulent actors sometimes give bogus IDs to avoid being charged VAT. If you don’t verify, you risk being part of a chain that tax authorities decide to audit.

You need proof of due diligence

Auditors will likely ask how you knew your customer was VAT-registered. A screenshot or log of your check is evidence that you did the right thing.

It keeps your invoicing and reporting clean

If a VAT number is invalid, the invoice might not qualify as a valid VAT invoice. That can block your customer from reclaiming VAT, and it can complicate your records.

How do you check a Dutch VAT number?

Every EU country formats VAT numbers differently. Dutch VAT numbers follow a specific format, so checking them requires precision, especially for sole proprietors.

Steps to verify a Dutch VAT number

1. Get the full VAT ID from your customer
   In the Netherlands, the VAT identification number (btw-id) starts with NL, followed by nine digits, then a B and two check digits.

2. Don’t confuse it with their RSIN
   Legal entities also get a second number: the RSIN. This is used only for filings, not invoices or cross-border sales. The RSIN looks similar but is tied to a business’s personal ID (BSN). That number won’t validate in the EU system, so always use the btw-id for VAT checks.

3. Use the EU’s VAT Information Exchange System (VIES) validation tool
   Go to the VIES website and select Netherlands (NL) from the dropdown. Next, enter the rest of the VAT number exactly as given, along with your VAT number. Finally, submit the form and wait for a live validation result.

4. Check the result
   If the VAT number is valid, you’ll see confirmation that the number is active, often with the registered business name and address. If it’s invalid, first double-check for typos and confirm you have the right number (btw-id, not RSIN). Follow up with the customer if needed.

Save a screenshot or timestamped record of the validation, especially if you’re applying reverse-charge VAT.

How do you use the EU VIES system for VAT validation?

The EU’s VIES is the official way to check whether a business is VAT-registered for cross-border transactions in the EU. The lookup tool queries each country’s VAT registry in real time.

With VIES, you can confirm whether a VAT number is valid and active. You can match the VAT number to a registered business, and some countries include an associated name and address. And you can generate audit-proof records of your validation activity.

To use VIES:

1. Go to the VIES site.

2. Select the country and enter the VAT number, including the two-letter prefix (e.g., DE, NL, FR).

3. Submit the query. VIES fetches data from that country’s tax authority instantly.

If the result is valid, you’ll see a confirmation message, often with a business’s name and location. If it’s invalid, that could mean a typo, a deactivated number, or the business hasn’t been activated for EU-wide trade. Recheck with the customer or consult the national authority if needed.

Save the validation result as a PDF or capture a screenshot. If questions arise later, this is the evidence that you did your due diligence.

What happens if a VAT number is invalid?

An invalid VAT number can trigger tax exposure, invoice issues, and audit risk. What happens next depends on when you catch it.

If you catch it before the sale

Simply charge VAT on goods as if it’s a domestic sale (you can’t zero-rate it). Next, ask the customer to confirm or update their VAT number. Avoid compliance issues by zero-rating only after the number checks out.

If you find out after the sale

You might owe back VAT even if the customer claimed to be VAT-registered. Other scenarios include issuing an invalid invoice, which means your customer might demand a credit note or reissue. Alternatively, penalties or interest could apply, depending on local rules and how the error was handled.

Tax authorities take this seriously because having a valid VAT ID is a legal condition for applying the 0% rate on intra-EU sales of goods.

If a VAT number ultimately doesn’t validate

Double-check everything first. Look over the formatting to make sure the VAT number has the country code, correct digits, and no typos. Confirm that you’re also using the right ID, such as the btw-id in the Netherlands. Ask the customer to verify with their tax office or to provide a new number.

How often should businesses verify VAT numbers?

A VAT number isn’t permanent. It can be deactivated, revoked, or changed, and if that happens and you don’t know, you’re the one exposed.

To guard against this, smart teams adopt basic habits regarding VAT numbers:

• Always verify at onboarding: Never apply reverse-charge VAT on goods without a valid number up front.

• Recheck regularly: Build in a quarterly or monthly verification cycle for active B2B customers. That catches changes before they become liabilities.

• Trigger rechecks on change: If a customer changes their business name, address, or VAT ID (or if anything feels off), run a new check immediately.

• Automate where possible: Systems can validate in real time and flag expired or invalid numbers before you issue an invoice.

If you’re audited, you’ll need to show when you last checked and that the number was still valid at the time of sale.

What tools can automate VAT number checks?

Manual checks work until you need to scale them. If you handle high volume or recurring EU sales, automation saves time and reduces risk.

There are several useful options:

• VIES application programming interface (API) integration: The EU provides a real-time validation API. You can build it into your billing or customer relationship management (CRM) system to check VAT numbers automatically at key points, such as signup, invoicing, or before zero-rating. VIES also has a batch request system that lets you submit multiple VAT numbers to be validated at once.

• Accounting or tax platforms: Many support bulk VAT validation and log results for audit trails.

• Payment platforms with tax logic: Stripe, for example, can validate VAT number formats during checkout, apply the right VAT treatment, and keep a record of the transaction, all without manual effort.

• Monitoring tools: These check stored VAT numbers on a schedule and alert you if one becomes invalid.

Set it up once, and every transaction becomes smarter, faster, and safer by default.

How Stripe Invoicing can help

Stripe Invoicing simplifies your accounts receivable (AR) process—from invoice creation to payment collection. Whether you’re managing one-time or recurring billing, Stripe helps businesses get paid faster and streamline operations:

• Automate accounts receivable: Easily create, customize, and send professional invoices—no coding required. Stripe automatically tracks invoice status, sends payment reminders, and processes refunds, helping you stay on top of your cash flow.

• Accelerate cash flow: Reduce days sales outstanding (DSO) and get paid faster with integrated global payments, automatic reminders, and AI-powered dunning tools that help you recover more revenue.

• Enhance the customer experience: Deliver a modern payment experience with support for 25+ languages, 135+ currencies, and 100+ payment methods. Invoices are easy to access and pay through a self-serve customer portal.

• Reduce back-office workload: Generate invoices in minutes and reduce time spent on collections through automatic reminders and a Stripe-hosted invoice payment page.

• Integrate with your existing systems: Stripe Invoicing integrates with popular accounting and enterprise resource planning (ERP) software, helping you keep systems in sync and reduce manual data entry.

Learn more about how Stripe can simplify your accounts receivable process, or get started today.