This package performs power calculations for randomized experiments that use panel data. Unlike the existing programs “sampsi” and “power”, this package accommodates arbitrary serial correlation. The program “pc_simulate” performs simulation-based power calculations using a pre-existing dataset (stored in memory), and accommodates cross-sectional, multi-wave panel, difference-in-differences, and ANCOVA designs. The program “pc_dd_analytic” performs analytical power calculations for a difference-in-differences experimental design, applying the formula derived in Burlig, Preonas, and Woerman (2017) that is robust to serial correlation. Users may either input parameters to characterize the assumed variance-covariance structure of the outcome variable, or allow the subprogram “pc_dd_covar” to estimate the variance-covariance structure from pre-existing data.