I present a new method for evaluating proposed reforms of progressive, piecewise linear tax schedules. Typically, estimates of the elasticity of taxable income (ETI) are used to predict taxpayer responses to changes in tax rates and/or tax bracket thresholds. I show that elasticities are not always needed for this task: the “bunching mass” at a bracket threshold (the share of taxpayers locating there) is a sufficient statistic for the revenue effect of behavioral responses to small changes of the threshold. Building on this finding, revenue forecasting and welfare analysis of threshold changes can be conducted using the pre-reform distribution of taxable income alone. I apply these results in an analysis of the Earned Income Tax Credit, an exercise which motivates extensions addressing optimization error, tax rate heterogeneity, and large reforms. This new use case for bunching complements existing bunching methods: it is robust to key limitations of bunching-based ETI estimation, but addresses a relatively narrow set of policy questions.