TaxSolver: A methodology to design optimal income tax reform

Résumé : Across the developed world, there are growing calls to streamline and improve ever more complex income tax codes. Executing reform has proven difficult. Even when the desired outcomes of a reform are clear, the tools to design fitting reforms are lacking. To remedy this, we developed \texttt{TaxSolver}: a methodology to help policymakers realize optimal income tax reform. \texttt{TaxSolver} allows policymakers to focus solely on what they aim to achieve with a reform -- like redistributing wealth, incentivizing labor market participation or reducing complexity -- and the guarantees within which reform is acceptable -- like limiting fluctuations in taxpayer incomes, protecting households from falling into poverty or shocks to overall tax revenue. Given these goals and fiscal guarantees, \texttt{TaxSolver} finds the optimal set of tax rules that satisfies all the criteria or shows that the set of demands are not mathematically feasible. We illustrate \texttt{TaxSolver} by reforming various simulated examples of tax codes, including some that reflect the complexity and size of a real-world tax system.