Optimal allocation between tax partners

Dutch Tax and Customs Administration

On this page, you will find information about the ‘Optimal allocation between tax partners’ algorithm. This algorithm automatically calculates the most tax-efficient allocation of tax deductions and joint income between partners who file a joint tax return.

Last change on 15th of July 2026, at 13:05 (CET) | Publication Standard 1.0

• Publication category: Impactful algorithms
• Impact assessment: Field not filled in.
• Status: In use

General information

Theme

Public finances

Begin date

Field not filled in.

Contact information

[e-mail]

Link to publication website

https://over-ons.belastingdienst.nl/onderwerpen/omgaan-met-gegevens/algoritmeregister/

Link to source registration

https://over-ons.belastingdienst.nl/onderwerpen/omgaan-met-gegevens/algoritmeregister/

Responsible use

Goal and impact

When filing a joint income tax return, tax partners must allocate joint income and tax deductions between themselves. In practice, it appears that many taxpayers do not achieve the optimal tax benefit in this regard. This can result in a higher tax burden than necessary. The algorithm does not apply to every joint tax return. It is only used when the tax situation lends itself to the automatic calculation of a tax-optimised allocation of joint income and tax deductions.

For tax returns involving certain complex tax situations or special tax schemes, such as business income, a substantial interest or certain asset and owner-occupied property situations, no automatic allocation proposal is therefore made.

The algorithm assists taxpayers in determining the most tax-efficient allocation. It does this by automatically calculating an allocation proposal based on the data entered. The user can accept this proposal or adjust it manually. In this way, the algorithm helps citizens to more easily submit an accurate and tax-efficient tax return. The outcome of the algorithm always represents tax optimisation, without taking into account any potential effects on other income-related schemes such as benefits.

Considerations

The process of automatically proposing an optimal allocation between tax partners in the tax return is important for citizens’ financial interests. We wish to carry this out with due care. The algorithm can assist a Tax and Customs Administration staff member in this regard. This makes the assessment more thorough, more efficient and more consistent.

The algorithm helps to systematically and accurately calculate a tax-efficient allocation of tax deductions and joint income. Using an algorithm allows these calculations to be carried out more quickly. This enables citizens to gain clarity on their expected tax liability more quickly.

The algorithm determines the assessment on the basis of the relevant data.

The alternative is for a citizen to carry out and check this allocation manually. This would make the process more prone to errors and less efficient.

Human intervention

Human intervention is always involved in the operation of the algorithm. The algorithm calculates a tax-optimised allocation proposal based on the data provided and displays this to the taxpayer in the online tax return environment. The taxpayer decides for themselves whether to accept this proposal or to apply their own allocation. Responsibility for the chosen allocation therefore lies with the taxpayer.

Risk management

The Tax and Customs Administration is taking various measures to manage the risks associated with the use of the algorithm.

• 1. Transparency

The Tax and Customs Administration publishes information about the algorithm in its own algorithm register and that of the central government.

This gives members of the public an insight into the use and functioning of the algorithm.

• 2. Automated decision-making

The description of an algorithm explains this and also elaborates on the aspect of human intervention.

• 3. Privacy protection and lawfulness

The Tax and Customs Administration ensures that the use of the data is assessed against the General Data Protection Regulation (GDPR).

The description of the algorithm also establishes the link with the applicable legislation and regulations.

• 4. Responsibility

The Tax and Customs Administration’s Algorithm Register policy framework clearly sets out and safeguards the responsibilities and tasks involved in the use of algorithms.

• 5. Monitoring and evaluation

The functioning of the algorithms is periodically reviewed. Selection rules may be adjusted on this basis.

Legal basis

1. General Act on Central Government Taxes: 
2. General Administrative Law Act: 
3. General Data Protection Regulation: 
4. General Data Protection Regulation Implementation Act: 
5. Income Tax Act 2001:
6. Citizen Service Number (General Provisions) Act:
7. Archives Act 1995: 

Links to legal bases

• General Act on Central Government Taxes:: https://wetten.overheid.nl/BWBR0002320/
• General Administrative Law Act:: https://wetten.overheid.nl/BWBR0005537/
• General Data Protection Regulation:: https://eur-lex.europa.eu/legal-content/NL/TXT/HTML/?uri=CELEX:32016R0679
• General Data Protection Regulation Implementation Act:: https://wetten.overheid.nl/BWBR0040940/
• Income Tax Act 2001:: https://wetten.overheid.nl/BWBR0011353/
• Act on General Provisions Relating to the Citizen Service Number:: https://wetten.overheid.nl/BWBR0022428/
• Archives Act 1995:: https://wetten.overheid.nl/BWBR0007376/

Elaboration on impact assessments

The use of the data must be assessed in accordance with the GDPR.

The GDPR stipulates that no more data may be used than is necessary. This is known as data minimisation. The Tax and Customs Administration regularly reviews whether the data used is still necessary and may therefore be used. 

Operations

Data

1. Identification details (national) – identification number/BSN | Basic Register of Persons (BRP)
2. Income tax return details | Tax and Customs Administration
3. Details of joint tax deductions | Tax and Customs Administration
4. Data on joint income | Tax and Customs Administration
5. Tax credits eligible for set-off and their redeemability | Tax and Customs Administration

Technical design

The algorithm consists of selection rules drawn up by subject matter experts on the basis of legislation, regulations and their expertise.

Using the data from the tax return and pre-defined calculation rules, the algorithm calculates a tax-optimised allocation of joint income and allowable deductions between tax partners. This proposed allocation is presented to the user as an option in the online tax return environment (OLAV).

The outcome of the algorithm is a proposed allocation that results in the lowest possible joint amount of tax due. The user can accept this proposal or manually select a different allocation.

The algorithm is not self-learning. This means that the algorithm does not adapt itself whilst in use.