Taxes: Calculation of local tax amount

Municipality of Rijswijk

The algorithm calculates the level of municipal taxes on the basis of fixed calculation rules. It uses data on the tax base, the benchmark and the corresponding rate. The algorithm performs these calculations automatically so that the tax amount for citizens and businesses can be determined efficiently and uniformly.

Last change on 9th of December 2025, at 12:19 (CET) | Publication Standard 1.0

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

General information

Theme

Public finance

Begin date

2021-10

Contact information

[e-mail]

Responsible use

Goal and impact

The purpose of this algorithm is to efficiently, reliably and uniformly calculate tax amounts for various local levies (such as waste collection, sewerage and property tax).

The impact on citizens and businesses is limited: the algorithm only determines the amount due based on statutory rates and set standards. The final assessment is always determined by a levy official.

Considerations

The use of fixed calculation rules ensures equal treatment of citizens and businesses. Without these automatic calculations, human calculation errors or inconsistencies in similar situations would be more likely. The algorithm contributes to transparency and accountability: the calculation rules used are based on public tax regulations.

Human intervention

The calculated amounts are always checked and determined by a levy officer. Spot checks and system checks take place to ensure that the calculation rules have been correctly applied.

Risk management

The algorithm has low risk because it does not learn or decide on its own, but only applies fixed formulas. Potential risks, such as incorrect rate input, are mitigated by: - annual monitoring of the rates in the tax ordinances; - test calculations before commissioning; - spot checks by the Taxation Department.

Legal basis

• Municipal Act
• General Act on national taxes (AWR)
• Property Valuation Act (WOZ)

Links to legal bases

• Municipal Act: https://wetten.overheid.nl/BWBR0005416
• AWR: https://wetten.overheid.nl/BWBR0002320
• Property Act: https://wetten.overheid.nl/BWBR0007119

Operations

Data

The algorithm uses data from municipal tax records, including:

• tax base (e.g. WOZ value, plot size or number of persons);
• basis and rate per tax type (e.g. waste disposal charges, sewerage charges, dog tax);
• object and address data from the Basic Register of Addresses and Buildings (BAG) and the WOZ administration.

No personal data are processed beyond what is necessary for taxation under the law.

Technical design

The algorithm consists of fixed formulas programmed into the tax application by the supplier. The calculation usually proceeds as follows:

1. The tax base is retrieved from the municipal records.
2. Based on the measure, the appropriate rate is selected.
3. The system multiplies the benchmark by the rate and applies any graduated rates.
4. The result is displayed as a calculated tax amount.
5. A levy officer checks and finalises the assessment.

The system includes internal controls to identify discrepancies or incorrect entries. The operation is deterministic: the same input always leads to the same outcome.

External provider

Centric Netherlands BV