While the final regulations largely follow the proposed regulations, they do contain some twists that may come as a surprise to clients who are currently in the midst of calculating their 2018 tax liability. Importantly, small business clients have the surprise option of relying on either the proposed regulations or the final regulations in finishing their 2018 taxes—although the final regulations become mandatory beginning in 2019. Despite this, clients must take an all-or-nothing approach to choosing which set of regulations to follow for 2018, making it important that they understand the important aspects of both the proposed and the final regulations now.  The analysis is here