Give a stream of consciousness and then the final answer. The House passed the penultimate version of the bill on December 19, 2017, though for Senate procedural reasons small changes were needed and a revote was held in the House. The Senate passed the final version on December 20 in a 51 -- 48 vote and that final version was passed by the House of Representatives on that same day. The bill was signed into law by President Donald Trump on December 22, 2017. Most of the changes introduced by the bill went into effect on January 1, 2018 and will not affect 2017 taxes.

Based on this passage, when does new tax rules go into effect?
The relevant information to answer the above question is: Most of the changes introduced by the bill went into effect on January 1, 2018 and will not affect 2017 taxes.
So, the final answer is January 1 , 2018.