Trump still thinks he can reach 4% GDP growth. Here's how often that happens

Donald Trump still thinks his policies can boost American GDP growth to 4 percent, more than double the average rate the U.S. has seen in this century.

In a speech to an energy conference in Pittsburgh on Thursday, the Republican presidential candidate claimed his tax cut and deregulation plans could boost U.S. growth to 4 percent or more. He first made the bold prediction in a speech earlier this month, saying "my great economists don't want me to say this, but I think we can do better" than 4 percent.

Trump, the billionaire developer, has touted himself as a pro-growth candidate and better economic alternative to Democrat Hillary Clinton. Trump has promised broad tax cuts, deregulation of the U.S. energy industry and increased spending on infrastructure and the military, leading some outside groups to estimate he would expand the deficit much more than Clinton would.

Despite those deficit projections, voters have generally felt Trump is better prepared to handle the U.S. economy than Clinton. He held a 46 percent to 41 percent advantage on the issue in the NBC/ Wall Street Journalpoll released Wednesday.

Andrew Harrer | Bloomberg | Getty Images

Donald Trump, 2016 Republican presidential nominee, speaks at the Marcellus Shale Coalition conference in Pittsburgh, Pennsylvania, U.S., on Thursday, Sept. 22, 2016.

Reaching 4 percent GDP growth may prove just as difficult as implementing broad tax cuts without making the deficit climb. The U.S. economy grew at roughly 2 percent in 2015 and last expanded at a 4 percent annual rate in 2000.

That feat has only proven more difficult in recent years. Since 1947, the U.S. economy has grown at a 4 percent or higher quarterly rate 104 out of 277 quarters, or 37.6 percent of the time. It has reached that threshold in only 26 of 106 quarters, or 25 percent of the time, since 1990.

In a fact sheet released earlier this month, the Trump campaign outlined a goal of 3.5 percent average annual GDP growth for the next decade. The American economy has reached that growth goal on a quarterly basis only 36 out of 106 times, or 34 percent, since 1990.

The right-leaning American Enterprise Institute highlighted the challenges with Trump's 4 percent goal earlier this month. It said that GDP growth has slowed since the mid-20th century partly due to a labor force growth slowdown as baby boomers retire.

His prediction could also require a large productivity boost and more immigration, which Trump has pledged to make more difficult.

— CNBC's Steve Liesman and Gina Francolla contributed to this report.