Perhaps you, like 99.983 percent of Americans, are not familiar with residence trusts as a means of reducing estate tax bills. (We made up that percentage.) Perhaps you are also in the 99.987 percent of Americans who aren't particularly worried about whether or not the estate you leave your kids will exceed $5.3 million. (That one, too.)

But maybe, just maybe, you are curious just how much the Clintons -- you know, Bill and Hillary -- saved on their estate taxes by using a sophisticated planning tool. We were, so we asked an expert.

The question was prompted by an article from Bloomberg on Tuesday. Richard Rubin reported that the Clintons created a residence trust on the home they own in New York state, in an effort to reduce the amount of taxable assets they would pass on in their estate. The piece was framed as a bit of hypocrisy, the Clintons seeking to avoid paying the very taxes that they have advocated as policy. For that to be an effective critique, however, there's one key question: How much were the Clintons actually saving?

To answer that, we first have to go over how estate taxes work. We spoke with Alban Salaman, mid-Atlantic region chair of private wealth services for the law firm of Holland & Knight, who walked us through the legal requirements.

The first key number is $5,340,000. That is how large your estate can be without it being taxed by the federal government. That's the figure in 2014; it changes over time. And it's cumulative, so if you leave your kid a $5 million estate and a $500,000 sports car, you're $160,000 over the max. Anything over the "exemption amount," as it's known, is taxed at 40 percent. So your lucky kid would need to pay $64,000 in taxes. ($160,000 times 40 percent.) Simpler: Think of it like a bag at a candy store. Anything you fit in the bag you get free; anything else, you have to pay for. You're going to do your best not to overfill that bag.

So let's say you're planning ahead for your estate. You know that you're going to give that kid the house and the car. And you know that those things will increase in value over time, meaning that they'll use a larger part of your estate tax exemption. Salaman used the example of stock: "Apple is selling now for approximately $90/share. So if I gave my daughter 1,000 shares now, it used up $90,000 of my exemption. Why would I want to do that? [Because] by the time I die in 20 years, that's going to be worth triple or quadruple, but I'm only using part of my exemption." (Note: You invest in Apple stock based on Salaman's projection at your own risk.)

The Clintons apparently plan to leave at least their home in Chappaqua, N.Y., to their daughter, Chelsea. According to Bloomberg, the New York house is worth $1.8 million per its property tax assessment. If they gave it to Chelsea outright, right now, they'd each use $900,000 of their $5.3 million exemptions. (Assuming they own the house jointly and choose to do so. We'll get into that later.) But the home's value is likely to go up between now and when the Clintons die. So they'd like to give it to Chelsea now, when it's worth less.

But they also don't want to give up their house. So: "What if she had to wait seven years?" Salaman asked rhetorically. "They give it to her in a way that they still own it for seven years, and then she owns it." By making the transfer happen in the future, the Clintons (or anyone else who creates a residence trust) both get to use the house and lock in its value for their heir(s).

And there's another benefit, too. Making the gift in a few years' time means that the present value of the house is lower. This is tricky, so bear with us. In 10 years (the length of time the Clintons reportedly set for their trust), the house will be worth more than $1.8 million, as noted above. But the beneficiary of the increase is Chelsea, not the Clintons. So for the purposes of estate planning, the house is worth $1.8 million as a gift, even 10 years later. And a gift of $1.8 million in 10 years is worth less than $1.8 million today. It's as though I'd pledged in 2004 to give you $100 right now. That $100 was only worth about $80 10 years ago. That's the same sort of gulf that the Clintons get to take advantage of.

So in 2011, what the Clintons did was transfer the ownership of the Chappaqua house to two trusts, one controlled by Bill and the other by Hillary. (The IRS would demand that the Clintons get the house formally appraised, given that tax assessments tend to be lower than the sale value.) The trusts agree to transfer the house to Chelsea in 2021. The Clintons (or, more likely, their attorneys) use IRS tables to figure out the present value (versus the appraised value that the gift will be worth in 2021). And then the Clintons would know how much of their estate exemption they had used in transferring the house to Chelsea.

There's a reason for them to split it between them. If one of the two dies before the house is transferred to Chelsea, that person's trust, half of the 2011 value of the house, reverts to the present-day value as a gift. By splitting it into two parts, the other half is still protected.

(Curious what happens after 10 years? If, in 2021, the Clintons want to keep living in that house -- or if they're moving back from a larger house in the Washington area -- they need to pay Chelsea rent. This, Salaman says, is why people often create these trusts for their vacation homes. Who wants to have to rely on their kid as a landlord?)

Now the big question: How much did they avoid in taxes? And the big answer: Well, it depends on a number of things, including things unrelated to the house itself.

Let's say they transferred the house in June 2011 and that it appraised at $1.8 million. Instead of each of the Clintons eating up $900,000 of their estate exemption, they likely only would have each used about $500,000, based on the calculated present value.

If, instead, they'd given the house to Chelsea in 2021 without protecting themselves from the estate tax, the house would at that point probably be worth, say, $2.6 million (assuming a four percent increase in value). That's $1.3 million used from each Clinton's exemption -- or $800,000 more than through the trust. In the chart below, it's roughly the difference between the green bar at left and the one at right.

Okay. If they'd already filled up that $5.34 million exemption (or whatever it is in 2021) and they're getting taxed on that extra $800,000 apiece -- if, in other words, the green bar in the chart above sticks above the dotted line by $800,000 -- they'd be paying $320,000 in tax, each or $640,000 total.

But that scenario is unlikely for a variety of reasons, requiring that they've maxed out their exemption and so on. Nor is this some sort of exotic tax vehicle that only savvy consumers know about. "The qualified personal residence trust is directly in the statute and regulations, with examples," Salaman said. "This is not something odd. This is just normal estate planning for wealthy people."

That's a point we made last week. The Clintons are wealthy people, who've gotten consistently more sophisticated about how they plan their finances as they've grown wealthier. Hypocrisy is in the eye of the beholder on the issue of estate taxes. But if Hillary or Bill Clinton ever suggests that they are average Joe Americans, still trying to scrape a few nickels together, feel free to remind them how long it took to explain their estate plans.