Tax cuts and repatriation should help some stocks more than others.
In a perfect world, cutting the U.S. corporate tax rate could immediately send the broad stock market as much as 11 percent higher, S&P Global Market Intelligence said in a report released Thursday.
But looking at the tax rates for companies last year, industries such as health insurers and homebuilders might benefit more from corporate tax cuts than other sectors.
Most of the companies that are based in the U.S. have a high tax rate as most of their sales come from within the country, said Dan Clifton, head of policy research at Strategas Research Partners. When looking for potential outperformers as tax law changes, he's looking for "companies with a lot of domestic income but also companies with limited exposure to international" inputs.
CNBC analyzed a list of S&P 500 names with tax rates between 10 and 45 percent in fiscal 2015 and excluded companies with rates outside that range as they were likely influenced by accounting measures or one-time tax credits.
Health insurers Anthem, Aetna and UnitedHealth topped the list with tax rates of nearly 43 percent or more in fiscal 2015, according to S&P Dow Jones Indices. Lowe's and Masco, a manufacturer of home improvement products, had tax rates of more than 42 percent.
Those rates are far above the 15 percent rate U.S. President-elect Donald Trump has proposed. The current corporate tax rate is 35 percent, while the effective rate, or the one that companies in the S&P 500 actually pay after deductions, is below 30 percent.
The weighted average tax rate for the S&P 500 overall was 26.7 percent in the second quarter of this year, Howard Silverblatt of S&P Dow Jones Indices said.
Clifton expects the tax rate could be negotiated down to 25 percent. He's also watching for beneficiaries of Trump's proposed one-time 10 percent tax rate on repatriated corporate profits that are now held offshore.
The United States has one of the highest corporate tax rates in the world, and many U.S. companies with large overseas operations have chosen to set up subsidiaries in other countries where the tax rate is much lower. The companies do not need to pay U.S. taxes on the profits earned by overseas operations until the earnings are brought back to the United States.
Energy and information technology generate more than 57 percent of their sales from foreign sources, versus 44.4 percent for the S&P 500 overall, according to S&P Dow Jones Indices.
As a result, information technology had the lowest average tax rate in the second quarter, at 17.4 percent, the S&P data showed. Energy was next at 17.8 percent in the second quarter, according to the data.
Note: REITs included in financials.
On the other hand, domestically focused sectors had some of the highest tax rates and stand to benefit the most from large tax cuts.
Telecommunication services had the highest average tax rate of nearly 38.3 percent in the second quarter, followed by industrials and consumer staples, which had average tax rates of 28.4 percent in the second quarter, S&P data showed.
Looking beyond the largest U.S. stocks by market capitalization as covered by the S&P 500, small-cap stocks are expected to benefit the most as their businesses focus on the U.S. economy.
— CNBC's Patti Domm and Jeff Cox contributed to this report.