Invoicing Basics for Small Business Owners

TL;DR: A legally valid invoice must include specific information (your business details, a unique invoice number, line item descriptions, and applicable VAT/GST). Invoices are the foundation of your accounts receivable and tax records — formatting errors cost you money and credibility.

What You Need to Know

Invoicing seems simple — you sell something, you send a bill. But invoicing law is more specific than most founders realize. In VAT/GST-registered countries, invoices must include mandated fields or they may be invalid for the recipient's tax purposes. In B2B sales, clients may reject a non-compliant invoice and delay payment until a corrected version is issued. In regulated industries, invoicing requirements are even more specific.

Beyond compliance, professional invoicing practice directly affects your cash flow. Late payment is endemic in business — the average payment time in the UK is 37 days against a standard 30-day term. Strong invoicing practice (clear terms, follow-up processes, late payment provisions) significantly reduces the gap between invoice issue and cash in account.

This guide covers what legally compliant invoices look like across seven countries, best practices for getting paid on time, and the tools that can help.

How It Works: A Practical Overview

Mandatory Invoice Fields (VAT/GST-Registered Businesses)

Once registered for VAT/GST, invoices must include legally mandated information. Non-compliant invoices cannot be used by the recipient to claim input VAT — meaning you may owe your client a refund or correction.

Standard VAT invoice (UK, France, Sweden) must include:

• The word "Invoice" (or equivalent in French: "Facture"; Swedish: "Faktura")
• A unique sequential invoice number
• Invoice date
• Your full business name and address
• Your VAT registration number
• The recipient's name and address (and VAT number for B2B invoices in some cases)
• A clear description of goods or services supplied
• The date of supply (if different from invoice date)
• The net amount (excluding VAT) for each line item
• The applicable VAT rate for each line item
• The VAT amount for each line item
• The total net amount
• The total VAT amount
• The total gross amount (including VAT)

For reverse charge VAT (where the recipient accounts for VAT): The invoice must state "reverse charge" and the applicable reverse charge mechanism.

Simplified invoices: In the UK and EU, businesses may issue simplified VAT invoices for supplies under GBP/EUR 250. Simplified invoices may omit some fields (recipient details, itemized VAT amounts) but must include the VAT registration number and gross amount.

Invoice Fields for Non-VAT-Registered Businesses

If you are not yet VAT/GST registered, you must NOT include a VAT number or charge VAT on your invoices. Your invoice still needs:

• Your business name and contact details
• A unique invoice number
• Invoice date
• Description of goods/services
• Total amount due
• Payment terms and bank details

Professional Invoice Best Practices

Payment terms: State clearly when payment is due ("Net 30 days from invoice date"). In the UK, the Late Payment of Commercial Debts (Interest) Act 1998 provides a statutory right to charge 8% above Bank of England base rate on late B2B payments. In France, maximum payment terms are 60 days from invoice date or 45 days from end of month (whichever comes first) under French commercial law.

Bank details: Include IBAN (international) or sort code/account number (UK). For international clients, include SWIFT/BIC code.

Late payment clause: Include an explicit late payment clause referencing your statutory or contractual right to charge interest. Even if you never exercise it, it prompts faster payment.

Invoice numbering: Maintain a sequential numbering system (INV-001, INV-002). Never repeat or skip numbers — gaps raise audit flags.

Issue promptly: Issue invoices immediately upon delivery of goods or completion of services. Every day of delay in issuing an invoice is a day added to your payment wait.

Invoice Software

Purpose-built invoicing software handles the compliance elements automatically:

• FreshBooks (freshbooks.com)
• Xero (xero.com) — strong in UK, Australia, NZ
• QuickBooks (quickbooks.intuit.com) — strong in US, UK
• Debitoor (debitoor.com) — strong in Sweden, continental Europe
• Wave (waveapps.com) — free tier available
• MYOB (myob.com) — strong in Australia, NZ

Most accounting software includes configurable invoice templates that automatically populate your VAT number, bank details, and payment terms.

Country-by-Country Comparison

Common Mistakes to Avoid

1. Charging VAT on an invoice before you are registered. Charging VAT without a valid VAT number is fraud. If a customer pays VAT to you and you are not registered, they cannot reclaim it, and you have received money you are not legally entitled to. Check your registration status before including VAT on any invoice.
2. Issuing invoices without sequential numbering. Tax authorities look for numbering gaps as a potential indicator of suppressed sales. Maintain a clean, sequential numbering sequence. If you need to cancel an invoice, issue a credit note rather than deleting or renumbering.
3. Not including the recipient's VAT number on EU B2B invoices. For EU VAT purposes, zero-rating of B2B supplies within the EU (Intra-Community supplies) requires the customer's VAT number on the invoice. Without it, standard-rate VAT applies. Always collect and verify customer VAT numbers for EU B2B sales.
4. Not following up on overdue invoices. Many businesses issue invoices and then passively wait. A structured follow-up sequence — automated reminder at 1 day before due date, another at due date, a call at 7 days overdue — dramatically reduces average debtor days without damaging customer relationships.
5. Using the wrong invoice template for different supply types. Different supply types (standard-rated, zero-rated, exempt, outside scope) require different invoice treatments. Using a single template that includes VAT on everything may incorrectly charge VAT on exempt or zero-rated supplies.

Next Steps: Get Started Today

MmowW Scrib🐮 provides compliant invoice templates for each jurisdiction, designed to meet VAT/GST requirements.

• Filing Deadlines: Know exactly when your VAT/GST returns are due → Filing Deadlines Tool
• Cost Calculator: Estimate the cost of invoicing tools and accounting software → Cost Calculator Tool

MmowW Scrib🐮 is a document preparation service, not a law firm. We do not provide legal advice. For specific VAT/GST invoicing requirements, consult a qualified accountant or tax advisor in your jurisdiction.

Frequently Asked Questions

Q: Do I need to send invoices in the customer's language?

A: In France, French law requires commercial documents (including invoices) to be in French for domestic B2C transactions. For B2B transactions with foreign customers, dual-language invoices are common and generally acceptable. In other jurisdictions (UK, Australia, USA), there is no statutory language requirement for invoices. However, providing invoices in your customer's language is good business practice.

Q: What is a pro forma invoice and when should I use it?

A: A pro forma invoice looks like a final invoice but is clearly marked "Pro Forma" and is not a demand for payment. It is used to: (a) give customers a preview of costs before accepting an order, (b) facilitate customs clearance for international shipments (as evidence of anticipated transaction value), or (c) request advance payment before supplying goods or services. A pro forma is not a VAT/GST invoice — it does not create a VAT obligation. The final invoice issued upon delivery does.

Q: Can I charge interest on overdue invoices?

A: Yes, in most countries. In the UK, the Late Payment of Commercial Debts (Interest) Act 1998 provides a statutory right to charge 8% above Bank of England base rate on overdue B2B invoices, plus a fixed debt recovery cost. In France, interest can be charged at the rate specified in the invoice terms or at the ECB rate + 10 points. In Australia and New Zealand, contractual interest on late payments is enforceable. In the USA, the terms depend on the contract and state law. Always include your late payment terms in both the original contract and the invoice.

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