Invoicing – Definition, Legal Requirements & Practical Tips

Invoicing refers to the process of issuing bills – that is, creating, sending, and managing invoices for services rendered or goods delivered. In an HR context, it primarily concerns billing from external service providers such as staffing agencies, freelancers, or recruiting firms. For an invoice to be legally valid under German law, it must include all mandatory details required by §14 of the German VAT Act (Umsatzsteuergesetz, UStG).

What Is Invoicing? Definition and Meaning

Invoicing is the commercial process by which a company creates, sends, and records an invoice (from the Latin factura, meaning "production" or "bill") for services rendered or goods delivered.

The invoicing process encompasses more than simply producing the document. It also includes verifying completeness, sending the invoice to the recipient, recording it in the company's accounting system, and – where necessary – following up on outstanding payments. Professionals responsible for this process on a day-to-day basis are known as billing clerks or invoicing specialists.

Invoicing vs. Payroll: What Is the Difference?

The two terms are often used interchangeably in everyday language, but they refer to different processes. Invoicing means issuing a bill to an external third party – a client or commissioning party. Payroll, by contrast, refers to internal processes or the remuneration of employees, such as monthly salary settlements.

For HR professionals, the distinction matters: payroll is a separate area governed by employment law. Invoicing, on the other hand, covers service agreements with external partners.

What Does a Billing Clerk Do?

A billing clerk works in a commercial or accounting role and is responsible for the entire invoicing workflow: creating accurate outgoing invoices, reviewing incoming invoices for correctness and completeness, and supporting the finance department. In HR settings, these responsibilities are often handled by HR administrators in coordination with the accounting team.

Legal Requirements: What Must an Invoice Contain?

Under German law, the requirements for a legally valid invoice are set out in §14 UStG. If mandatory details are missing, the invoice may not be recognised for tax purposes – and the recipient may lose their right to deduct input VAT (Vorsteuerabzug).

Mandatory Details Under §14 UStG

According to §14 UStG, an invoice must include the following:

• Full name and address of both the issuing company and the recipient
• Tax number or VAT identification number of the issuer
• Date of issue
• Sequential invoice number (unique, non-repeating)
• Quantity and standard commercial description of goods delivered, or the nature and scope of services rendered
• Date or period of supply or service
• Net amount (excluding VAT)
• Applicable VAT rate (typically 19% or 7%) and the corresponding VAT amount
• Gross amount (total including VAT)

For low-value invoices under €250 (gross), simplified requirements apply under §33 of the German VAT Implementing Regulation (UStDV).

Retention Periods for Invoices

Both outgoing and incoming invoices must be retained for ten years under §147 of the German Fiscal Code (Abgabenordnung, AO) and §257 of the German Commercial Code (Handelsgesetzbuch, HGB). The retention period begins at the end of the calendar year in which the invoice was issued. This obligation also applies to digitally created or received invoices – their storage must comply with the GoBD (Grundsätze zur ordnungsmäßigen Führung und Aufbewahrung von Büchern), Germany's principles for proper bookkeeping and record retention. In practice, this means invoices must be archived completely, in an unalterable format, and remain accessible at all times.

Net vs. Gross Invoicing

In B2B transactions, the distinction between net and gross invoicing is essential for accurate accounting.

When Does Net Invoicing Apply?

With net invoicing, the invoice amount is stated without VAT – the tax is shown separately and itemised. This is the standard in B2B contexts, as companies can reclaim the VAT charged as input tax against their own VAT liability. Invoices from external HR service providers, freelancers, or recruiting agencies are typically issued on a net basis.

When Does Gross Invoicing Apply?

Gross invoicing states the total amount including VAT, without breaking out the tax separately – or it includes a note that tax is already included. This format is more common in B2C contexts, when companies bill end consumers. For HR professionals, gross invoicing is less common, but can arise when processing minor service expenses such as catering receipts or small miscellaneous charges.

Invoicing in the HR Context

Although invoicing is primarily an accounting matter, it intersects with day-to-day HR work at several points – particularly wherever external service providers are involved.

Reviewing Invoices from External HR Service Providers

Staffing agencies, external recruiters, training providers, and assessment vendors regularly submit invoices to HR departments. When reviewing incoming invoices, HR professionals should check the following:

• Does the service description match the agreed terms and conditions?
• Are all mandatory details under §14 UStG present?
• Is the service date correctly stated?
• Does the VAT rate correspond to the type of service rendered?

Incorrect invoices should be queried promptly – a corrected invoice is a prerequisite for claiming input VAT. Close coordination with the accounting department is strongly recommended.

Reverse Charge for Foreign Freelancers

HR teams that commission foreign freelancers or agencies for recruiting projects or HR initiatives may encounter the reverse charge mechanism. Under §13b UStG, the tax liability is reversed: instead of the service provider, it is the receiving company – i.e., the HR client – that owes the VAT to the German tax authorities.

In practice, this means the foreign freelancer's invoice will not include German VAT. The commissioning company must calculate the tax itself, report it in its VAT return, and can simultaneously claim it as input tax. For HR professionals without an accounting background, it is advisable to coordinate such cases with the finance or tax department, or to consult a tax adviser.

Common Invoicing Mistakes – and How to Avoid Them

Faulty invoices delay payments, jeopardise input VAT recovery, and create unnecessary administrative burden. The most common errors in HR environments:

Missing or incorrect mandatory details: A missing tax number, an undisclosed service date, or a duplicated invoice number can render an invoice legally vulnerable. Using a checklist helps to avoid these errors systematically.

Wrong VAT rate: Not all services are subject to the standard rate of 19%. Certain training programmes, coaching services, or VAT-exempt transactions may be subject to different rates. When in doubt, consult a tax adviser.

Non-compliant digital archiving: Simply leaving invoices in an email inbox does not meet GoBD requirements. Digital invoices must be archived in an unalterable, structured format.

Reverse charge not identified: Invoices from abroad without VAT are sometimes mistakenly perceived as "cheaper" – when in fact the tax liability falls on the receiving company. If this is overlooked, back-payments and interest charges may follow.

Frequently Asked Questions About Invoicing

What Is Invoicing?

Invoicing refers to the process of issuing bills for services rendered or goods delivered. The term covers the creation, sending, review, and accounting recording of invoices. In commercial practice and within HR, it primarily concerns the settlement of accounts with external service providers.

What Is the Difference Between Invoicing and Payroll?

Invoicing refers to billing external third parties – clients or commissioning parties. Payroll, by contrast, typically refers to internal processes, such as the monthly settlement of employee salaries. The two terms are often used interchangeably in everyday language but are legally and accountingwise distinct.

What Mandatory Details Must an Invoice Include Under §14 UStG?

A legally valid invoice under §14 UStG must contain: full names and addresses of both parties, the issuer's tax number or VAT ID, the invoice date, a sequential invoice number, a description of the goods or services, the service date, the net amount, the applicable VAT rate, the VAT amount, and the gross total.

What Is the Difference Between Net and Gross Invoicing?

Net invoicing states the amount excluding VAT, with the tax shown separately – this is the B2B standard. Gross invoicing includes VAT in the total amount, and is more common in B2C contexts. For HR departments, net invoices from external service providers are the norm.

What Is Reverse Charge – and When Is It Relevant in HR?

Under the reverse charge mechanism (§13b UStG), it is the invoice recipient – not the issuer – who owes VAT to the tax authorities. It applies, among other cases, when commissioning foreign freelancers or service providers. HR departments that work with international agencies or external IT contractors are frequently affected.

How Long Must Invoices Be Retained?

Both outgoing and incoming invoices are subject to a statutory retention period of ten years (§147 AO, §257 HGB). The period begins at the end of the calendar year in which the invoice was issued. Digitally archived invoices must also be stored in a GoBD-compliant manner: complete, unalterable, and accessible at all times.

Conclusion

Invoicing is more than simply issuing a document: it involves a structured process with clear legal requirements – from the mandatory details under §14 UStG, to the distinction between net and gross billing, to special provisions such as the reverse charge mechanism. HR professionals regularly encounter incoming invoices from external service providers and should be familiar with the key fundamentals in order to avoid errors and additional costs. Close collaboration with the accounting department – and, where tax law questions arise, with a qualified tax adviser – is strongly recommended.

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Sources

• §14 UStG – Issuance of invoices. Federal Ministry of Justice, 2024.
  https://www.gesetze-im-internet.de/ustg_1980/__14.html
• §14a UStG – Additional obligations when issuing invoices. Federal Ministry of Justice, 2024.
  https://www.gesetze-im-internet.de/ustg_1980/__14a.html
• §13b UStG – Recipient of supply as tax debtor (Reverse Charge). Federal Ministry of Justice, 2024.
  https://www.gesetze-im-internet.de/ustg_1980/__13b.html
• §147 AO – Obligations regarding retention of records. Federal Ministry of Justice, 2024.
  https://www.gesetze-im-internet.de/ao_1977/__147.html
• GoBD – Principles for the proper keeping and storage of books, records, documents and data and for data access. Federal Ministry of Finance, 2019. https://www.bundesfinanzministerium.de/Content/DE/Downloads/BMF_Schreiben/Weitere_Steuerthemen/Abgabenordnung/2019-11-28-GoBD.html