As Hillary Clinton and Donald Trump prepare to meet in the final presidential debate tonight, the people who put their money where their mouth is are signalling that the result is pretty well baked in.

Prediction markets -- exchange-traded markets that allow investors to make bets on the outcome of events -- make Clinton an odds-on favorite to win the White House, just as they have ever since Trump clinched the Republican party's nomination in May. The markets moved in her favor after the first presidential debate and have climbed since, boosted by her rival's unconventional tactics and many missteps and largely unaffected by problems of her own.

U.K.-based market Betfair lists the former secretary of state at a roughly 83% likelihood of becoming the next president. PredictIt and the Iowa Electronic Markets, both in the U.S., list her chances at about 82% and 87%, respectively.

PredictWise, which aggregates prediction market data as well as polls, currently gives Clinton a 90% chance at victory.

"This cycle, they're all pretty consistent," said Eric Zitzewitz, professor of economics at Dartmouth College who has studied prediction markets.

In fact, Clinton's chances may be better than the markets indicate. Though prediction markets have, historically, been very accurate at forecasting elections, one error they consistently make is that they overprice long shots slightly.

In other words, if something is trading at 85% odds, it tends to happen about 90% of the time.

"If you were to think that was happening here as well, then Clinton's odds may be even higher," said Zitzewitz.

Nate Silver's FiveThirtyEight model currently gives Clinton an 87.4% chance of winning the presidency. A RealClearPolitics poll average has her ahead of Trump by 7.5 points in a two-way matchup and by 7.3 points when including third-party candidates Gary Johnson and Jill Stein.

Wednesday's debate at the University of Nevada Las Vegas could change the shape of the race and, in turn, the markets.

"[Wednesday's debate] is Trump's final chance to be part of the conversation," said David Rothschild, a New York-based Microsoft Research economist and creator of PredictWise.

The first presidential debate between President Barack Obama and former Massachusetts Governor Mitt Romney in 2012 resulted in a shift in Romney's direction. This year, prediction markets moved towards Clinton during the first showdown.

Later-stage debates have had an effect as well, as in the 2000 matchup between President George W. Bush and former Vice President Al Gore. The markets swung about four points towards Bush after the second debate and about four points back to Gore after the third.

These events were the exception, not the rule. Since 1988, those are the only instances of debates proving especially meaningful in terms of betting odds.

"Most of the other debates had hardly any impact at all," said Zitzewitz.

To be sure, prediction markets are not a surefire signal of an election's outcome. They largely missed the mark on the Brexit vote for the U.K. to leave the European Union.

But many consider them a useful measure for anticipating likely outcomes. Prediction markets are a sort of crowd-sourced indicator based not on what people want to happen but rather on what they think will happen -- and are willing to put their money on. They also move faster than polls.

"The markets react very quickly. It takes time to field a poll, digest the results, get it out there," said John Aristotle Phillips, CEO of PredictIt, in a recent interview with TheStreet.

Prediction markets at times also mirror movements of the broader markets at large. They have this election cycle.

As the prediction markets reacted to the first Clinton-Trump debate, so did measures like the S&P 500, VIX futures indices and the Mexican peso. They remained relatively unchanged during the second debate, as did the S&P.

"The markets were pretty quiet," said Zitzewitz.

Wednesday marks the third and final presidential debate of the general election cycle, and as such, it promises fireworks. But will it tip the scales enough for those putting their own money on the election's outcome to change their bets to Trump?

"Unless he wins big, expect the markets to creep up for Clinton in the last few days before Election Day," he said.