The March 2021 update to PovcalNet involves several changes to the data underlying the global poverty estimates. Some welfare aggregates have been changed for improved harmonization, and the CPI, national accounts, and population input data have been updated. This document explains these changes in detail and the reasoning behind them. In addition to the changes listed here, a large number of new country-years have been added, resulting in a total number of surveys of more than 1,900. Moreover, this update includes important revisions to the historical survey data and for the first time, poverty estimates based on imputed consumption data.