Digital common

OpenFisca is a digital common: it is free and open source software designed, developed and used by many people around the world through democratic, horizontal governance processes such as Requests For Comments (RFCs) and open discussions.


As contributors to a common, we collectively do our best to make our community a space where everyone can express themselves and feel free to be who they are. Our rules to that end are grown progressively as we learn what works and what doesn’t. If you encounter or witness any behaviour in an OpenFisca-related space that does not seem respectful, please open a discussion in the OpenFisca Slack space or send an email to the core team.


The development of OpenFisca began in May 2011 at the French Centre d’analyse stratégique (renamed France Stratégie in April 2013), with the support of the Institut d’économie publique (IDEP, Aix-Marseille).

OpenFisca was originally developed as a desktop application using the Qt library with a Python API. This source code was released under a free software (AGPL) license in November 2011.

In early 2014, the French Prime Minister task force for open data, Etalab, started using OpenFisca and soon became a major contributor. After organising a hackathon to give more visibility to the product, its team decided to:

  • stop the development of the Qt version;
  • separate the computing engine from its desktop user interface;
  • offer a web API in addition to the Python API;
  • demonstrate the value of the web API by developing sample applications including a web interface to simulate personal cases;
  • offer public access to this web API.

The core was improved extensively by Etalab, while the French model was improved and updated by the Commissariat général à la stratégie et à la prospective (CGSP) with the help of the IDEP and the Institut des politiques publiques (IPP). A few months later, the French State Startups incubator started using the API and extending the model for digital public services purposes, delivering a first consolidated benefits assessment tool targeting citizens, Mes Aides, and a payroll simulator.

In 2016, the Open Government Partnership (OGP) Paris Summit demonstrated the international value of OpenFisca when a small team of OpenFisca France maintainers and OpenFisca Tunisia volunteers managed to model Senegal’s income revenue tax in under 36 hours, with a simulator shipped complete with a web UI during the OGP hackathon, winning the team the first prize.

This led, in 2017, to a joint effort from Etalab and to improve stability, reusability, and ease of contribution. This resulted in major technical improvements, a full rewrite of the documentation, the launch of to replace, and the addition of new contributors from other French agencies as well as new international reusers with an experiment from Italy and the city of Barcelona delivering a benefit assessment tool.

In 2018, the product manager that had led the internationalisation efforts moved to Aotearoa New Zealand, where the recently established Service Innovation Lab was finishing writing its Better Rules report. This foundational theoretical piece matched perfectly with OpenFisca’s implementation of “turning legislation into code”, leading to the Rates Rebate app, the first service in production outside of Europe. Other areas in the Pacific region (Australia, Polynesia, Canada) were progressively exposed to OpenFisca and adopted it.

In 2019, OpenFisca is recognised as most innovative open source software by the European Commission through the Joinup program.
On the same year, the first LexImpact simulator is created by the French National Assembly, enabling members of parliament to evaluate reforms on both test cases and the whole French population within a few seconds.

In 2020, considering the growing adoption across administrations and the critical mass of contributors, the French Interministerial Direction of Digital Affairs (DINUM) decided to stop funding efforts to grow and maintain OpenFisca, suggesting these should be funded collectively by reusers. A minimal core team was maintained through funding from the French Agence nationale de la cohésion des territoires (ANCT), but usage growth and technical improvements slowed down significantly as no clear business model was established.

In 2021, members of civil society started modelling British and then USA legislation, leading to the creation of PolicyEngine.

In 2022, as usage grew in several countries without clear contributions to an increasingly outdated engine, means for sustained operation of OpenFisca independently from any single State were assessed by the core team on the ANCT funds.

In 2023, the OpenFisca community is distinguished among over 1,000 candidates screened by the OECD and is awarded the Edge of Government Innovation Award at the World Government Summit.