Four million.  

That is how many words are in the US tax code (known as the Internal Revenue Code or IRC).  At a normal pace of reading one hundred words per minute and 10 hours a day (spending the rest of the time fighting boredom), it would still take you over two months to read it cover to cover.  Granted, included in the Standard Federal Tax Reporter reference publication is not only the current regulations but also all of the rulings and case law that provides interpretations.  

Not only do you need to know the rules to calculate your taxes correctly, it requires knowing all of the official reinterpretation of the rules.  Complexity takes time.  

It is estimated by WalletHub that in 2019 US tax payers will spend 8.1 billion hours on tax preparation to navigate the layers upon layers of brackets and exemptions and deductions.  That is a tremendous loss of productivity.  

Think about it.  That is the equivalent of 3.24 million work years (at 10 hours per day, 250 work days a year) or roughly 2% of total work in the US per year (labor force of around 160 million people).  The complexity has grown over the decades exponentially.  

Perhaps the next tax reform should seek to save US tax payers their time.