Tax Planning
  
What will you owe? For most people, tax planning is kind of a meh issue. That is, they work for a corporation that automatically takes out a pretty-close-to-reality amount of dough from their monthly paychecks. At the end of the year, they get a small refund, or pay a bit more to true things up. No big. No fuss. No muss.
But, for entrepreneurs or risk-takers in the markets, tax planning becomes a much bigger deal.
Two years ago, you started the year with $3 million in savings. It was all invested in publicly traded stocks. That amount doubled last year to be $6 million; you sold no stocks. Then, this year, it doubled again to $12 million and you sold everything. Turned it all into cash.
Well, you have then realized a gain (likely all long-term) of $9 million, and you'll owe about 40% tax on that money, or a tax of about $3.6 million.
That $9 million jet you were gonna buy? Yeah. Don't do that. You don't have enough money. You'll have to plan for that $3.6 million. And, in most cases, you'll owe portions of it quarterly. And it'll mess with your following year's investments. You might have losses you'll want to harvest as you realize gains in the future. The losses you have from investing the $8.4 million in cash you'll put back to work at some point will be valuable tax hedges. And, in the real world, individuals not subject to simple corporate salary tax withdrawals have to pay quarterly contributions. That is, they must make scheduled payments along the way during the year, or suffer fines in various forms and flavors. (See: Safe Harbor.)
All of these moving numbers get extremely complex, as you'd imagine. So rules were set up wherein individual tax payers could vastly simplify their returns by simply paying 110% of whatever they paid in the same quarter last year. That way, there are no fines for investors realizing gains who just didn't realize that they owed all that tax.
Yes, all of this is complex, but it needs to be. Otherwise, how would we keep so many accountants and lawyers employed?