If the gap between price gains and EPS growth as stocks priced in 2017 tax changes is any guide, we calculate the S&P 500's trailing P/E ratio may drop 3-4% to account for a possible increase in the statutory corporate tax rate under a new administration. In 2017, the index rose 19.4% and EPS grew 12%. As monetary policy was tightening that year as the balance sheet held steady and the Fed steadily raised rates, the 7.4-point gap between the two can be viewed as what investors priced into multiples at the time, anticipating the Tax Cuts and Jobs Act of 2017, passed in December.A similar hit to the current 24.3x trailing P/E multiple would take the S&P 500 to 22.5x, but since the Biden plan implies an increase in the corporate tax rate half as large as the 2018 decline, we posit the P/E adjustment may be half as great.