What Every Invoice Must Include: Legal Requirements by Country
Every invoice needs 10 mandatory fields to be legally valid and get paid faster. Covers EU, UK, US, and country-specific rules — no fluff.
Every invoice must include: the word "Invoice," a unique invoice number, issue date, payment due date, your business details, the client's details, an itemized list of goods or services, a financial summary with tax, the currency, and payment instructions. Missing any of these can delay payment, fail a VAT audit, or make the invoice legally unenforceable.
This guide covers those universal requirements and adds country-specific rules for the EU, UK, US, Germany, and France.
Universal Invoice Requirements
Regardless of where you operate or who you're billing, these elements should appear on every invoice:
1. The Word "Invoice"
Label your document clearly as "Invoice" at the top. This seems obvious, but some businesses use "Bill," "Statement," or just their company name — which can cause processing delays and confusion in accounts payable departments.
2. Unique Sequential Invoice Number
Every invoice needs a unique reference number that follows a sequential or date-based pattern. This is essential for tracking, auditing, and dispute resolution. Rules for invoice numbering:
- Numbers must be unique — never reuse a number, even for voided invoices
- They must be sequential with no unexplained gaps
- Consistent formatting across all invoices
3. Issue Date
The date the invoice was created and sent. This is the starting point for calculating payment due dates and determines when the transaction is recognized for tax purposes.
4. Supply Date (Date of Service or Delivery)
The date the goods were delivered or the service was completed — this is separate from the invoice date. Many tax authorities (including HMRC and EU member states) require this field when it differs from the issue date. For ongoing services, a period (e.g., "March 1–31, 2025") is acceptable.
5. Payment Due Date
Always include a specific due date rather than just "Net 30." Clear, concrete deadlines (e.g., "Due: February 28, 2025") reduce ambiguity and late payments.
6. Your Business Details
- Full legal business name (exactly as registered)
- Complete business address
- Email address
- Phone number
- Tax identification number (where required by law)
7. Client's Details
- Client's full legal name or company name
- Complete billing address
- Shipping address if different from billing address (for physical goods)
- Contact person and email for B2B invoices
- Client's tax ID for B2B transactions (required in many jurisdictions)
8. Itemized Description of Goods or Services
For each line item:
- Clear, specific description of the product or service
- Quantity (units, hours, days, etc.)
- Unit price
- Any applicable discounts at line-item level
- Line total
9. Financial Summary
- Subtotal (before taxes and discounts)
- Any overall discounts applied
- Tax rate and tax amount (clearly labeled)
- Grand total due
10. Currency
Always specify the currency, especially for international clients. Don't assume "dollars" or "euros" is obvious — clients in different countries may interpret this differently.
11. Payment Terms
State your payment terms explicitly: the due date, accepted payment methods, any early-payment discount (e.g., "2% if paid within 10 days"), and late-payment interest if you charge it. Many jurisdictions allow — and some require — a late interest clause. In France, for example, the €40 flat-fee recovery indemnity must appear on every B2B invoice.
12. Payment Instructions
Include all information needed to make payment: bank account details (account number, sort code for UK, routing number + account number for US, IBAN/SWIFT for international), PayPal email, or a payment link. The easier you make it to pay, the faster you get paid.
VAT Invoice Requirements (European Union)
If you're VAT-registered in the EU, your invoices have additional mandatory requirements under the EU VAT Directive (Council Directive 2006/112/EC):
- Your VAT registration number (format varies by country: DE123456789, GB123456789, FR12345678901)
- Customer's VAT number for all B2B transactions
- VAT rate applied to each line item (or group of items at the same rate)
- Total VAT amount in the invoice currency
- Invoice amount excluding VAT (net amount)
- Invoice amount including VAT (gross amount)
- If the reverse charge mechanism applies, state "Reverse charge" or "VAT: Reverse charge"
- If zero-rated (e.g., export), state the legal basis for zero-rating
Simplified VAT invoices: For amounts under €400 (threshold varies by member state), simplified invoices may be permitted. However, full VAT invoices are always the safer choice.
UK Invoice Requirements (Post-Brexit)
UK VAT-registered businesses must include:
- Your UK VAT registration number (format: GB followed by 9 digits)
- VAT rate applied (20% standard, 5% reduced, or 0% zero-rated)
- Amount of VAT charged
- Total invoice amount excluding VAT
- Date of supply if different from invoice date
- Bank details: sort code and account number for domestic payments; IBAN and SWIFT/BIC for international transfers
- Note: Businesses in Northern Ireland supplying goods to EU customers follow EU VAT rules; Great Britain follows UK rules only
US Invoice Requirements
The US has no single federal invoice format, but several requirements apply in practice:
- Sales tax must be shown as a separate line item if applicable — rates and rules vary by state, county, and city
- For bank transfers, include your routing number and account number (ACH details)
- For government contracts, specific formats and line-item codes are required under FAR regulations
- Some states have industry-specific requirements (e.g., construction, legal services)
- Payments to US contractors exceeding $600/year require a W-9 on file — the invoice itself should reference the contractor's business name exactly as on their W-9
Germany-Specific Requirements (§ 14 UStG)
- Your Steuernummer (tax number) or Umsatzsteuer-Identifikationsnummer (USt-IdNr.)
- Sequential invoice number with no gaps
- Date of supply (Leistungsdatum) if different from invoice date
- Gross and net amounts clearly separated
- Kleinunternehmer: must state "Gemäß § 19 UStG wird keine Umsatzsteuer berechnet"
France-Specific Requirements (CGI Art. 289)
- Your SIRET number (14-digit business registration number)
- Your TVA (VAT) intracommunautaire number for B2B invoices
- Late payment penalties must be stated
- Recovery indemnity clause (€40 flat fee for late payment) must be mentioned
- Auto-entrepreneurs: must state "TVA non applicable, art. 293 B du CGI"
Common Compliance Mistakes to Avoid
- Missing VAT number — Required for all VAT-registered businesses; prevents customers from reclaiming input VAT
- Incorrect client VAT number — Verify via the EU VIES system before issuing invoices
- Skipped invoice numbers — Creates audit red flags and is illegal in many jurisdictions
- No payment due date — Creates ambiguity and delays
- Vague item descriptions — "Services rendered" is not acceptable in most tax jurisdictions
- Wrong currency notation — Use ISO 4217 codes (USD, EUR, GBP) rather than just symbols
- Missing legal basis for zero-rating — For exempt or zero-rated supplies, state the legal reason
FAQ
Does every invoice need a VAT number?▼
Only if you are VAT-registered in a country that requires it. In the EU and UK, VAT-registered businesses must include their VAT number. If your revenue is below the VAT registration threshold, you do not need to include a VAT number and cannot charge VAT.
What happens if I send an invoice without all required information?▼
Your client may not be able to reclaim VAT, leading to disputes. Tax authorities may disallow your income records during an audit. In some jurisdictions, non-compliant invoices may not be legally enforceable for payment.
Can I use the same invoice template for different countries?▼
Yes, but you may need to adjust certain fields. For example, you'll need different tax number fields for EU vs UK vs US clients. A good invoice generator handles these differences automatically.
Do I need a purchase order number on my invoice?▼
Only if your client requires it. Many large companies need a PO number to match invoices to their procurement records. Always ask new clients whether they need a PO number before sending your first invoice.
What is the difference between an invoice and a receipt?▼
An invoice is a request for payment issued before or at the time of delivery. A receipt is a confirmation of payment issued after money changes hands. Invoices are the legally relevant documents for tax and VAT purposes; receipts are proof of settlement.
Do I need to include payment terms on every invoice?▼
Yes — and they should be explicit. "Net 30" means the full amount is due within 30 days of the invoice date. If you charge late payment interest, state the rate and the legal basis (e.g., the UK Late Payment of Commercial Debts Act 1998 allows 8% above the Bank of England base rate). Without stated terms, enforcing late fees in court becomes much harder.
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