Jeb Bush released more tax returns than any other presidential candidate in history. Over 33 years, the former Florida governor's campaign said he paid an average effective tax rate of 36 percent.

... depending on how you calculate it.

That's a confusing number, and it obscures three decades in which Bush's income climbed slowly, then explosively.

Scrutinizing politicians' tax returns can be wonky, tedious business, but it matters because the documents are also used as political weapons. So understanding how candidates manipulate their tax figures becomes all the more important.

By portraying his effective tax rate as high, Bush not only gets to portray himself as a fair-and-square taxpayer, but also make a point about what he sees as the problems of the U.S. tax system. He also used it to compare himself with Hillary Clinton, the Democratic front-runner, whose 2014 tax returns showed she and her husband, former President Bill Clinton, paid a 30 percent rate.

The Math Behind The 36 Percent

To come up with Bush's 36 percent number, the Bush campaign did a straightforward calculation, adding up his total taxes from 1981 through 2013 and dividing it by all of the income he earned in those same years.

That's simple enough, but it makes that headline "36 percent" figure easy to misunderstand. For one thing, saying it was his "average tax rate" could suggest that he, in fact, paid an average of 36 percent each year — that is, that he paid something around 36 percent each year.

That's not close to true.

Really, he paid more than 36 percent in only eight of those years. (Meanwhile, in four earlier years, he had either zero or negative taxable income.)

Here's how that 36 percent number works, then: Bush made a huge share of his money in the last few years. Two-thirds of his taxable income came in just the last five years of returns, to be exact.

Not only that, but a new 39.6 percent bracket went into effect in 2013, as Yahoo contributor and financial planner Michael Kitces pointed out. Not only does that give the most recent years extra weight, but the campaign also isn't adjusting for inflation, so the earliest years get even less weight than they should.

Not to get too wonky, but one might more precisely call this figure Bush's total effective rate from 1981 to 2013. The average effective rate, simply adding together all the rates and then averaging them out, was more like 24.5 percent.

Kitces was the first to do something like this — using slightly different figures from the Bush tax returns, he came up with a 21 percent rate.

And that's how effective tax rates work — no one talks about or thinks about their total tax rate over time, because income changes year by year, as do tax brackets (not to mention the tax laws governing those brackets). Adding them up over time doesn't really say anything meaningful.

How Jeb Bush Is Like LeBron James — High Tax Rates

Still, there's no denying that in the past few years, Bush paid a lot of money to the government, relative to his fellow high earners. Bush earned $7.2 million in taxable income in 2013 and paid $2.7 million in income taxes, an effective income tax rate of 36 percent that year.

That year, the effective tax rate for people in the top 0.1 percent of earners (who had an average income of around $) was 26 percent. That puts him in stark contrast to another rich Republican political scion who recently ran for president. Mitt Romney took a lot of heat in the 2012 cycle for his 14 percent effective tax rate and the methods he took to get to that low number.

In light of these figures, many are asking why Bush didn't find a way to pay less.

"For me, what stands out is that he doesn't appear to have been aggressively trying to legally avoid his taxes," said Joe Thorndike, director of the Tax History Project at Tax Analysts. "Most people with a lot of money pay a lot of money to tax advisers to minimize their taxes. They pay a lot, but it saves them even more. It really doesn't look like he did much of that."

The Bush campaign also highlighted this with a statement from Abraham Shashy, former IRS chief counsel:

"All of the returns appear to me to have been prepared conservatively and timely," he wrote, adding, "There is no indication of aggressive or improper tax planning."

There is some explanation for why Bush's rate is so high for an uber-rich person — one is that a lot of his income was in self-employment. Bush only ("only") earned around $662,000 in capital gains in 2013 — income from investments like stocks or real estate — making those a small share of his total income. Those capital gains are generally taxed at a lower rate than wage income. In this way, you can think of Bush (at least from a tax perspective) as more LeBron James than Mitt Romney.

"The short answer is that there is nothing he can do [to lower his rate on his self-employment income], because he is providing personal services," Lee Sheppard, contributing editor at Tax Analysts, said, adding, "Many people with those [high] incomes earn capital gains, but that is because they get their money from wealth, not personal services. But there are some people, like Bush, who earn their large paychecks from services, like sports figures."

There are other avenues Bush could have taken to lower his rate as well. As McClatchy's Lesley Clark and Amy Sherman point out, Bush has donated less to charity than even than the average American — he gave away 1.5 percent of his adjusted gross income in 2013, compared to the 3 percent average for other Americans. In contrast, fellow candidate Carly Fiorina gave away 13 percent in 2013.

Not only that, but he's including something the rest of us don't have in our income tax returns — payroll taxes.

When most workers get their paychecks, employers take out some taxes. They pay half of the payroll taxes, and workers pay the other half. Bush, however, is self-employed, so he pays his own self-employment taxes through his income-tax return.

Bush includes those in his effective tax-rate calculations. When he says he paid more than 40 percent last year, that's not just income tax — it's those Medicare and Social Security taxes, too. It's not a huge amount, accounting for around 3 percentage points in 2013, but that extra padding works to Bush's advantage, as part of his point he's sending with his tax returns is that he believes tax rates need to be lowered.

"This release will show voters how I earned a living over the past three decades and how much of that living I had to give back to Uncle Sam. (Spoiler Alert: A LOT)," he wrote in an essay accompanying the returns.

25 Percent, 36 Percent ... Why Do We Care?

It's a busy pre-election season, and making these sorts of distinctions about the math candidates are using on their taxes can seem like the smallest of matters.

But in a hard-fought election, tax returns can easily be weaponized. The Obama campaign used Romney's lower tax rate and high income to stoke voter resentment and play into a narrative about Romney as uncaring. That bore fruit. By Election Day, when asked in exit polls which candidate cared about "people like me," Obama won the question 81 to 18 percent.

As a result, many observers saw Romney's lack of foresight in preparing his pre-election tax returns as a major misstep. But what Bush seems to understand is that tax returns aren't private tallies of income and deductions — they're campaign documents.

"My impression of these returns is that they [the Bush campaign] are politically astute, like many people running for office, but more than some — certainly more than Mitt Romney," Thorndike said.

James Joseph, head of the Tax Group at law firm Arnold and Porter, agrees that it appears Bush prepared these returns with an eye toward caution.

"[Bush] seems to have just been very careful," he said, drawing a contrast to Romney. "Romney had so much going on even in what he disclosed that raised questions. It was almost as if he did no planning at all from a campaign perspective."

While being rich is rapidly becoming a requirement for seeking national office, the trappings of being rich — like a team of tax-dodging accountants — can turn voters off. The goal for Bush's team: Being able to tell voters that he, too, hates paying Uncle Sam. That may well make even a high earner like the candidate seem more relatable.

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