This paper investigates whether taxpayers bunch at the kink points of the US income tax schedule, using tax returns data from 1979 to 1994. The study finds clear evidence of bunching only at the first kink point (where marginal rates jump from 0 to 15%), with stronger evidence for itemizers than for non-itemizers. Theoretical models suggest that bunching is proportional to the compensated elasticity of income with respect to tax rates. These models are used to simulate income distributions and calibrate key parameters to the empirical income distributions. The results indicate that, except for low-income earners, the behavioral elasticity consistent with the empirical results is small. The paper also explores the impact of uncertainty on bunching, finding that it smooths out the humps in the income distribution. Overall, the findings suggest that taxpayers do not bunch perfectly at kink points but tend to cluster around them, with the degree of bunching influenced by the elasticity of income to marginal tax rates and the extent to which taxpayers control their income.This paper investigates whether taxpayers bunch at the kink points of the US income tax schedule, using tax returns data from 1979 to 1994. The study finds clear evidence of bunching only at the first kink point (where marginal rates jump from 0 to 15%), with stronger evidence for itemizers than for non-itemizers. Theoretical models suggest that bunching is proportional to the compensated elasticity of income with respect to tax rates. These models are used to simulate income distributions and calibrate key parameters to the empirical income distributions. The results indicate that, except for low-income earners, the behavioral elasticity consistent with the empirical results is small. The paper also explores the impact of uncertainty on bunching, finding that it smooths out the humps in the income distribution. Overall, the findings suggest that taxpayers do not bunch perfectly at kink points but tend to cluster around them, with the degree of bunching influenced by the elasticity of income to marginal tax rates and the extent to which taxpayers control their income.