U.S. companies stand to reap a "huge benefit" from the new Republican tax law, which includes a dramatic corporate rate cut, said the head of portfolio strategy at Merrill Lynch Wealth Management.

"We're anticipating at least earnings going up an additional 10 percent than where we were without the tax plan," Mary Ann Bartels told CNBC's "Squawk Box" on Friday. "We were already seeing analysts raising their numbers. And now with the tax plan, we expect the numbers to go up even more."

As part of the tax law, the federal corporate tax rate was cut from 35 percent to 21 percent.

Expectations for strong earnings have helped propel the stock market to one of its best yearly starts in years, Bartels said.

Credit Suisse's chief U.S. equity strategist, Jonathan Golub, agrees with Bartels about the tax benefit to earnings and the market.

"About 25 companies have provided guidance on what's going to happen to their tax rate," Golub said in a later CNBC interview on Friday. Their earnings-per-share estimates for 2018 are "up 9 percent from the day before the tax change up until today," he said.

"For those companies who provided no guidance at all, they're up only 1 percent on their EPS" 2018 estimates, he said. "The EPS estimates are way too low; probably 7 or 8 percent more upside to 2018 EPS as that guidance trickles out."