EU VAT for B2B SaaS: A Practical Guide for Founders and Developers

If you sell software to businesses across EU borders, VAT is mostly about one thing: knowing when not to charge it, and being able to prove you were right. Here is the practical version — reverse charge, why you validate the buyer's VAT number, place of supply, and what to store.

The one rule that matters most: reverse charge

Under normal VAT rules the seller charges VAT and remits it. For cross-border B2B sales inside the EU, that would force you to register for VAT in every customer's country — clearly impractical for a SaaS company with customers in twenty countries. The reverse charge mechanism solves it: when you sell to a VAT-registered business in another member state, you issue the invoice with no VAT, and the buyer accounts for the VAT in their own country (usually netting to zero because they reclaim it on the same return).

For your billing system this means a binary decision at invoice time: charge local VAT, or zero-rate with a reverse-charge note. The note typically reads something like “Reverse charge — VAT to be accounted for by the recipient.” The full mechanics, including the conditions and wording, are covered in the VAT reverse charge guide.

Why you must validate the buyer's VAT number first

Reverse charge is conditional on the buyer actually being a VAT-registered business. If you zero-rate an invoice and the buyer's VAT number is invalid, cancelled, or fabricated, you have made a supply without charging VAT and without a legal basis for the exemption. The tax authority can then come back to you for the VAT, plus interest and penalties — money you never collected from the customer.

This is why VAT validation belongs in your checkout or onboarding flow, not in a quarterly accountant review. Before applying the reverse charge, confirm the buyer's number is currently valid in VIES (the EU's VAT Information Exchange System). You can run a one-off check with the free tool at vatnode.dev/check, or automate it with a single API call:

interface VatDecision {
  applyReverseCharge: boolean
  vatRate: number
  note?: string
  checkId?: string
  verifiedAt?: string
}

async function decideVatTreatment(
  buyerVatId: string,
  sellerLocalRate: number,
): Promise<VatDecision> {
  try {
    const res = await fetch(
      `https://api.vatnode.dev/v1/vat/${encodeURIComponent(buyerVatId)}`,
      { headers: { Authorization: `Bearer ${process.env.VATNODE_API_KEY}` } },
    )

    if (!res.ok) {
      // VIES temporarily unavailable — fail safe: charge VAT, retry async
      return { applyReverseCharge: false, vatRate: sellerLocalRate }
    }

    const result = await res.json()

    if (result.valid === true) {
      return {
        applyReverseCharge: true,
        vatRate: 0,
        note: 'Reverse charge — VAT to be accounted for by the recipient',
        checkId: result.checkId,
        verifiedAt: result.verifiedAt,
      }
    }

    // Known-invalid number — do not zero-rate
    return { applyReverseCharge: false, vatRate: sellerLocalRate, checkId: result.checkId }
  } catch (err) {
    // Network/unexpected error — be conservative and log
    console.error('VAT check failed:', err)
    return { applyReverseCharge: false, vatRate: sellerLocalRate }
  }
}

Place of supply, briefly

“Place of supply” is the rule that decides which country's VAT applies to a sale. For digital and electronically supplied services — which is what most SaaS is — the general B2B rule places supply where the business customeris established. That is precisely what makes the reverse charge work for cross-border B2B: the supply is treated as taking place in the buyer's country, and the buyer accounts for the VAT there.

Two practical consequences for a SaaS billing system:

• 1For B2B, you need the buyer’s country and a valid VAT number — both come out of the validation step, so capture and store them together.
• 2For B2C (selling to consumers), the place of supply is generally the consumer’s country and you charge that country’s rate, often reporting via the One-Stop Shop (OSS). That is a separate flow from this B2B guide.

Place-of-supply rules have exceptions and special cases. Treat the above as the common SaaS path, not legal advice, and confirm the specifics for your product and customer base with a tax adviser.

There is also a status question hiding inside place of supply: is the customer actually a business? The reverse charge depends on it. A buyer who provides a valid VAT number is treated as a business; a buyer who has none is generally treated as a consumer and falls into the B2C path. This is why the VAT number is doing double duty in your billing system — it determines both whether you can zero-rate and whichcountry's rules govern the sale. Capturing it correctly at the start of the relationship saves re-work later, especially if a customer's status changes when they register for VAT partway through a subscription.

What to store for audit

If you ever face a VAT audit, the question will be: how do you justify zero-rating these invoices? The answer is the records you kept at the time. For every reverse-charge invoice, store at minimum:

The single most valuable item is the consultation number — an EU-issued reference that proves you checked a specific VAT number at a specific time. How to capture and retain all of this is covered in the VAT audit trail guide.

Common mistakes to avoid

• Trusting a format check. A correctly formatted number can still be invalid. Always do a live VIES validation, not just a regex match.
• Checking once and never again. Registrations lapse; re-validate active subscriptions periodically.
• Hard-blocking on VIES downtime. An unavailable country node should not reject a legitimate customer — fail safe and retry.
• Not keeping evidence. A pass/fail in memory is worthless at audit. Persist the check ID, timestamp, and consultation number.
• Confusing B2B and B2C. Reverse charge is B2B only; consumer sales follow OSS rules and rates.

Frequently asked questions