EU’s Once-Only Principle: What It Means

The EU’s once-only principle means that citizens and businesses should provide the same information to public authorities only once, with authorities sharing that data among themselves where legally permitted. For businesses and public authorities, it reduces administrative burden, speeds up procedures, and cuts costs by eliminating repeated data entry and verification. This article explains how the principle works, what it means in practice, and what you need to know to prepare.

Formula

The calculator estimates the potential annual saving from the once-only principle: Total saving (€) = Time saved per procedure (hours) × Procedures per year × Hourly cost (€/hour). The variables are: t = time saved per procedure in hours, n = number of procedures per year, r = hourly cost in euros (including employee wages and overheads). The output is the annual monetary saving in euros.

Worked Example

Using the default values: t = 5 hours, n = 20 procedures, r = €50/hour. Calculation: 5 × 20 × 50 = €5,000. The total hours saved = 5 × 20 = 100 hours. So the annual saving is €5,000.

Background: Where the Once-Only Principle Comes From

The once-only principle (OOP) is a core concept in the EU’s digital government agenda. It emerged from the 2014 EU eGovernment Action Plan and was formalised in the Tallinn Declaration on eGovernment in 2017. The principle is embedded in the EU’s Single Digital Gateway Regulation (Regulation (EU) 2018/1724), which requires member states to make key administrative procedures fully online and to ensure that users do not have to submit the same data to different public authorities. The goal is to create a truly single digital market where cross-border business and mobility are as easy as domestic operations.

The once-only principle is not a single EU-wide IT system but a set of technical, legal, and organisational measures. It relies on interoperability frameworks, secure data exchange, and clear rules on data protection. The European Commission has promoted the principle through the European Interoperability Framework (EIF) and the Once-Only Technical System (OOTS), which is being rolled out under the Single Digital Gateway Regulation. The OOTS connects national registries and allows authorities to exchange evidence documents (e.g., company registration, VAT numbers, permits) across borders.

How the Once-Only Principle Works in Practice

For a business, the once-only principle means that when you register a company, apply for a permit, or report data to one authority, that information can be reused by other authorities without asking you again. This works through:

• Data registries: Basic company data (name, address, legal form) is stored in a national business register. Other authorities query that register instead of asking you.
• Evidence exchange: When you apply for a construction permit, the building authority can request your company registration directly from the business register, with your consent, rather than requiring you to upload a PDF.
• Cross-border access: Through the OOTS, an Italian company bidding for a public contract in Germany can have its Italian registration data automatically verified by the German authority.
• User control: You are notified when an authority requests your data, and you can see what was shared. Consent is required unless a legal basis exists.

For public authorities, the principle requires a shift from a “silo� approach to a “service-oriented� approach. Authorities must publish their data registers, use common data models, and connect to national and EU interoperability layers. The Single Digital Gateway Regulation lists 21 procedures that must be fully online by 2023, including business registration, VAT registration, and social security enrolment.

Benefits for Businesses

The main benefit is reduced administrative burden. According to the European Commission, administrative costs for businesses in the EU are around €150 billion per year, and the once-only principle is expected to reduce these by a significant share. Concrete examples:

• A logistics company that needs to submit the same driver and vehicle data to multiple member states for cabotage permits can do it once, and authorities share the data.
• A startup registering a subsidiary in another member state can reuse its parent company data, reducing setup time from weeks to days.
• When applying for public procurement, companies no longer need to provide certificates of no criminal record or tax compliance; authorities can retrieve them directly from the relevant registries.

The once-only principle also reduces errors: because data is entered once and reused, there are fewer typos, outdated records, and inconsistencies. This improves data quality and trust.

Challenges and Common Problems

Implementing the once-only principle is not trivial. Key challenges include:

• Data protection: Sharing personal data across authorities must comply with GDPR. The principle does not override data protection; it requires a legal basis for each exchange.
• Technical interoperability: Different member states use different formats and standards. The OOTS relies on common semantic standards, but mapping legacy systems is costly.
• Legal barriers: Some national laws require original documents or physical signatures. These must be amended to allow electronic evidence exchange.
• Trust: Authorities may be reluctant to rely on data from another member state if they cannot verify its authenticity. The OOTS includes evidence verification mechanisms, but trust takes time to build.
• Costs of implementation: Public authorities face upfront costs for system integration, training, and change management. Smaller municipalities may lack resources.

A common misconception is that the once-only principle gives authorities unlimited access to your data. In reality, data sharing is limited to what is necessary for a specific procedure, and the user is informed. Another misconception is that it only applies to cross-border situations; in fact, it also applies domestically, which is where most of the savings come from.

How to Prepare as a Business or Public Authority

For businesses, the practical steps are:

1. Ensure your company data in national registries is accurate and up-to-date, because it will be reused.
2. Familiarise yourself with the Single Digital Gateway portal (Your Europe) where you can find information on procedures and evidence requirements.
3. When applying for permits or reporting, check if you can authorise authorities to retrieve data instead of submitting it yourself.
4. Keep digital records of your registrations and permits; you may need to provide consent for sharing.

For public authorities:

1. Map your procedures and identify which data you collect repeatedly. Prioritise those with the highest volume.
2. Connect to national interoperability platforms (e.g., the national data exchange layer) and the EU OOTS.
3. Adopt common data standards (e.g., Core Vocabularies) to ensure semantic interoperability.
4. Train staff on data protection and the legal basis for data sharing.
5. Communicate with users about how their data is handled and the benefits of the once-only approach.

Comparison with Other Approaches

The once-only principle is often compared with the “data minimisation� principle in GDPR and with the “digital default� principle. Data minimisation says you should collect only what you need; once-only goes further by saying you should not collect it again if it already exists. Digital default means providing services online; once-only adds the reuse of data. It also differs from a “one-stop-shop� where you submit all data to a single portal; once-only allows you to submit to one authority and have it shared, but you may still interact with multiple authorities.

Costs and Safety Considerations

While the once-only principle saves money in the long run, there are implementation costs. For the EU, the OOTS development is funded through the Digital Europe Programme. For member states, costs include IT upgrades and staff training. However, the benefits typically outweigh the costs. For example, a study by the European Commission estimated that the once-only principle could save businesses and citizens up to €11 billion per year across the EU.

Safety and security are paramount. The OOTS uses secure channels, encryption, and audit logs. Data is only shared with authorised authorities and for specific purposes. The principle does not create a central database; it connects existing registries. This reduces the risk of a single point of failure or a massive data breach.

Frequently Asked Questions

Does the once-only principle apply to my business if I only operate in one country? Yes. The principle is implemented nationally, so domestic procedures also benefit. For example, when you register a company, the tax authority can retrieve the registration data instead of asking you to submit it again.

Can authorities share my business data without my consent? Only if there is a legal basis, such as a regulation that requires the exchange. In most cases, you will be notified and can see what was shared. Consent is required where no other legal basis exists.

What happens if an authority refuses to accept data from another authority? The Single Digital Gateway Regulation requires authorities to accept electronic evidence from other member states. If an authority refuses, you can complain through the Your Europe portal or the national contact points.

Is the once-only principle the same as the “only once� principle in GDPR? No. GDPR’s data minimisation limits what you can collect, while the once-only principle limits how often you collect the same data. They complement each other.

How do I know which procedures are covered? The Single Digital Gateway Regulation lists 21 procedures, but many more are covered by national implementations. Check the Your Europe portal for a full list.

Will the once-only principle reduce the need for notaries or official translations? In many cases, yes. Electronic evidence from another member state is accepted without legalisation or translation, though there are exceptions for certain documents like court judgments.

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in t | Time saved per procedure | hours | 5 | 0 | 1000
in n | Procedures per year | - | 20 | 1 | 10000
in r | Hourly cost (€) | €/hour | 50 | 0 | 1000
out total | Total annual saving | € | t * n * r | 0
out hours | Total hours saved | hours | t * n | 0