With the Federal Reserve expected to raise U.S. interest rates at a meeting this week, investors are wondering: How many more increases in borrowing costs can the economy handle?

The answer, it appears, is not that many.

The Fed, led by Chairman Jerome Powell, has been raising benchmark rates since 2015 to keep the economy from overheating and prevent inflation from spiraling out of control. Higher rates act as a brake on investment and therefore growth, since they usually push up borrowing costs for consumers and businesses, via mortgages, credit cards and corporate loans.

Currently, the U.S. rate is set in a range between 1.75% and 2%, up from near-zero in the years after the 2008 financial crisis. At this week's two-day meeting in Washington, which concludes Wednesday, the Fed is expected to raise rates again, by 0.25 percentage point. Another 0.25 percentage-point hike could follow in December, marking the fourth increase this year, or once every three months.

But next year, with most economists projecting that the stimulus will wear off from President Donald Trump's $1.5 trillion tax cut, investors are betting on just two more quarter-point hikes, based on trading in U.S. futures markets. At that point, the Fed's benchmark rate would be at 2.8%, just below the 2.9% that Fed officials say is the appropriate "longer-run appropriate policy path" - the level at which growth would neither be stimulated nor suppressed.

"It's closing in on a level of policy rates that are reflective of current economic activity," said Steve Blitz, chief U.S. economist at the forecaster TS Lombard.

A pause in the Fed's rate-setting cycle - or an end to it - would follow remarks by Powell in a speech last month that he wanted to avoid "moving too fast and needlessly shortening the expansion." It's a position that's likely to sit well with Trump, who has expressed frustration with the Fed's rate hikes, especially since the economy is likely to be an issue for voters in the November congressional elections.

Powell said in a speech last month that he continues to believe a "gradual" pace of rate hikes is appropriate, based on the latest economic data. 

Many investors have lamented Trump's decision to pursue a trade war with China, since some businesses are already canceling or delaying expansion plans due to the threat of higher tariffs, thus undercutting the economic stimulus from the tax cuts. But the Fed's interest-rate increases have probably also taken a toll.

The economy grew 4.2% in the second quarter, the fastest in four years. The unemployment rate is at 3.9%, close to an 18-year low. And wages rose 2.9% from a year earlier in August, the fastest in nine years.

That's a lot of superlatives. As Trump tweeted earlier this month, in characteristic Trumpian hyberbole: "The economy is booming like never before."

But most economists think the fillip from the tax cuts is already fading.

Beth Ann Bovino, chief U.S. economist for Standard & Poor's, said in a phone interview that she expects growth to slow to 2.5% in 2019 from an average 3% clip this year. Inflation, meanwhile, is expected to hold steady over the next few years at 2.2%, she said, not too far above the 2% level targeted by the Fed.

In terms of rate increases, "We are seeing the light at the end of the tunnel," Bovino said.