I present a simplification safe harbour based on tax administrative guidance for Pillar Two, the global minimum tax, developed together with Cedric Döllefeld, Joachim Englisch, Simon Harst, and Felix Siegel. It aims at reducing unnecessary compliance costs by avoiding ETR calculations if a minimum tax of 15% has already been paid. The simplification safe harbour consists of a two-level test to determine if a full GloBE ETR calculation is required from an MNE or if a simplified ETR calculation or no calculation at all is sufficient. The test consists of a country-level test and – only if necessary – an MNE-level test. The country-level test assesses a country’s tax system. It seeks to determine whether the national tax system has (too) low nominal tax rates or significant deviations between a country’s tax base and the GloBE income exist. The second level, the MNE-level test, is only carried out if the country-level test has identified potential ‘red flags’. Even if this second test is required, the simplification safe harbour offers a significant reduction in compliance costs. This reduction is achieved by relying on national tax data, which is readily available in firms, instead of highly adjusted accounting data.