(Reuters) - U.S. Vice President and Democratic presidential candidate Kamala Harris' proposed corporate tax hike ahead of the November Presidential elections could lower earnings for companies on the benchmark S&P 500 index by about 5%, analysts at Goldman Sachs said.

Last month, Harris proposed raising the corporate tax rate to 28% from 21% and ensure "big corporations pay their fair share," if she wins the election against Republican rival Donald Trump.

Goldman estimated that at a 28% taxation rate earnings of S&P 500 companies would take a 5% hit.

Adding taxation of foreign income and an increase in the alternative minimum tax rate to 21% from 15% could reduce earnings by as much as 8%, the analysts said.

On the other hand, Trump's proposed relief on the federal statutory domestic corporate tax rate to 15% from the current 21% would "arithmetically" boost S&P 500 earnings by about 4%.

"The current U.S. statutory corporate tax rate on domestic income is 26%, but the total effective tax rate paid by the typical S&P 500 company is 19%," the brokerage added.

Goldman projected with each 1 percentage point change in the U.S. statutory domestic tax rate the shift in S&P 500 earnings per share (EPS) would be slightly less than 1% or about $2 of S&P 500 EPS.

Harris' rise to the top of the Democratic ticket has re-energized a Democratic campaign that had harbored doubts about Joe Biden's chances.

Polls showed that Trump had built a lead over Biden but Harris has since edged ahead of the Republican candidate in some national opinion polls.