The Global Life-Cycle Optimizer – Analyzing Fiscal Policy's Potential to Dramatically Distort Labor Supply and Saving

Fiscal policy in the U.S. and other countries renders intertemporal budgets non-differentiable, non- convex, and discontinuous. Consequently, assessing work and saving responses to policy requires global optimization. This paper develops the Global Life-Cycle Optimizer (GLO), a stochastic pattern-search algorithm. The GLO robustly, precisely, and quickly locates global optima in highly complex fiscal settings. We use the GLO to study how a stylized U.S. fiscal system distorts workers’ labor supply and saving assuming standard preferences. The system incorporates kinks from federal personal income tax brackets, Social Security’s FICA tax, and a notch from the provision of basic income below a threshold. The GLO reproduces theoretically predicted earnings bunching and flipping over a remarkably wide range of wage rates. Saving distortions can be equally dramatic. Associated excess burdens range from substantial to massive. Restricting labor supply to full- or part-time work can eliminate flipping when it’s optimal and produce flipping when it’s sub-optimal. Joint filing can significantly reduce the earnings of lower-wage spouses relative to that of higher-wage spouses. The GLO can be applied to assess a country’s or state’s full set of work and saving disincentives. Consequently, it can facilitate analyses of structural labor supply and tax reform.