France opens the source code of tax and benefits calculators to increase transparency

Published on: 20/11/2016

To improve the transparency of the country’s tax and benefits systems, France has decided to open the source code of the simulators that government administrators use to perform their calculations. The opening of these algorithms falls within the scope of the Law for a Digital Republic, which came into force early in October 2016.


Policy Context

  • The French Law for a Digital Republic came into force on October 7. Article 6 of this law, which was co-created with the help of civil society, requires openness from French administrations that develop simulation software. Article 6 stipulates that administrations must publish “the rules defining the major algorithmic processes used in the realisation of their tasks when they are used for individual decisions”. This is the first law in France to address source code explicitly.
  • Before the law was implemented, the Administrative Court of Appeal (Paris) confirmed that the source code of public software can be considered an administrative document and can thus be accessed by citizens if requested. In 2014, a student requested the source code of fiscal software used by the Directorate of Public Finances (Direction générale des finances publiques – DGFIP). After DGFIP refused, the student made a request to the Commission d’accès aux documents administratifs (CADA), which regulates access to administrative documents. DGFIP refused the subsequent request from CADA, so the student took the case to a higher authority, the Administrative Court, and won.
  • France has had an open government strategy since 2014, when it joined the Open Government Partnership (OGP). France has co-chaired the OGP since October 2016 and organised the OGP Summit in Paris in December 2016.
  • France’s first OGP National Action Plan lists government actions on transparency, citizens’ participation, open data and related issues. Among its 26 commitments, number 16 says that “the country will encourage the opening of the state’s calculation models and simulators”. The SGMAP (Secrétariat Général pour la Modernisation de l’Action Publique  –General Secretariat in charge of modernising the public action ) is in charge of the project.

“Opening data quickly leads to the opening of rules and models that produce them, complement them and underpin public decisions. These algorithms and models are a powerful resource for promoting independent views and developing applications, as long as they are open source and can be managed through APIs,” the text said.

Commitment 16 deals with two issues:

  • Extend the opening of the models to other fields of public action. Continue to work with the various government departments to assist them in opening their model calculations and simulations”; and
  • “Create simulators from existing open models. Capitalize on the OpenFisca platform [see below] to expand to other areas of legislation and suggest variations of simulators useful to citizens, economic actors and public actors: for example a model of energy costs, an extension to cover local taxation, pension calculations...”

Description of the way to implement the initiative

Transparency is key to democracy

French President François Hollande said in a statement for the fifth anniversary of the OGP that “transparency is key to democracy”. As the head of OGP, France wants to make sure that democracy “is the most open, the most concrete, the most shared possible, and can become a hope for many peoples.” The President’s priorities include “sharing digital common goods”, “transparency in public and economic life”, and “ensuring that decisions taken in the public sphere are known to all, understood by all.”

54 calculators could be opened

Some French government departments, including DILA (Direction de l’information légale et administrative – Legal and Administrative Information Directorate) and DGFIP, develop algorithms that allow them to model the tax and benefits systems in France. To date, in fact, 54 simulators have been developed by French administrations. These simulators and calculators contain, in digital form, the mathematical rules needed to analyse data and make predictions. Since April 2015, ssthe source code of four of them has already been published.

First on the list: the fiscal calculator

On April 1, DGFIP, in collaboration with Etalab, the French agency in charge of Open Data and Open Government, officially opened the source code of the simulator used to calculate income tax. The code is now available on GitHub.

The administration even organised a hackathon, called “CodeImpôt”, to help public agents, developers, scientists and start-ups use the newly-opened code to create new projects or improve other simulators.

During the event, Michel Sapin, the French Minister of Finance said that income tax requires trust between the state and citizens: “This transparency is necessary to increase trust in our fiscal system.”

The team in charge of OpenFisca helped to make the DGFIP code accessible by developing tools to facilitate its re-use. OpenFisca is an open source project that has developed its own micro-simulator for the French tax and benefits systems. OpenFisca has acted as a foundation for other projects including, an official government simulator for state benefits. is one of the state start-ups incubated by DINSIC, the government IT department.


Last October, DILA decided to open three of its own simulators. The Directorate organised a new hackathon called “CodeGouv” to encourage the re-use of the algorithms.

As DILA explained, these three simulators are used by the French administration to:

  • Calculate the cost of a registering a motor vehicle. The cost of the registration card is made of different taxes, such as the regional tax or the ecological malus, whose application and calculation may prove difficult, DILA said
  • Calculate the penalties that public services face if they fail to make payments on time; and
  • Calculate the bonus payments that the government makes to apprentices.

Lessons learnt

Improving transparency helps to increase trust in democracy and in the social and fiscal system. Particular actions that have been shown to be effective during the opening-up of the French government simulators are:

- Promote the re-use of newly opened algorithms through hackathons to create new ideas and simulators, and to improve existing ones.

- Provide development tools, and make data available in formats that help people to re-use the published code.

- Build a global community made up of many different types of people: students, civil servants, scientists, entrepreneurs, developers and data scientists.

Scope: National


Type of document
General case study