BACKGROUND: Childhood obesity prevalence remains high in the U.S., especially among racial/ethnic minorities and low-income populations. Federal policy is important in improving public health given its broad reach. Information is needed about federal policies that could reduce childhood obesity rates and by how much. PURPOSE: To estimate the impact of three federal policies on childhood obesity prevalence in 2032, after 20 years of implementation. METHODS: Criteria were used to select the three following policies to reduce childhood obesity from 26 recommended policies: afterschool physical activity programs, a $0.01/ounce sugar-sweetened beverage (SSB) excise tax, and a ban on child-directed fast food TV advertising. For each policy, the literature was reviewed from January 2000 through July 2012 to find evidence of effectiveness and create average effect sizes. In 2012, a Markov microsimulation model estimated each policy's impact on diet or physical activity, and then BMI, in a simulated school-aged population in 2032. RESULTS: The microsimulation predicted that afterschool physical activity programs would reduce obesity the most among children aged 6-12 years (1.8 percentage points) and the advertising ban would reduce obesity the least (0.9 percentage points). The SSB excise tax would reduce obesity the most among adolescents aged 13-18 years (2.4 percentage points). All three policies would reduce obesity more among blacks and Hispanics than whites, with the SSB excise tax reducing obesity disparities the most. CONCLUSIONS: All three policies would reduce childhood obesity prevalence by 2032. However, a national $0.01/ounce SSB excise tax is the best option.