The secret to unlocking a further $US6 trillion ($A7.86 trillion) of gains in global stocks and adding another 10 years to this bull run? Forget tax cuts and share buybacks, women are key, according to research by S&P Global.
The United States lags developed country peers in terms of the share of women in work. Even if it just catches up with other economies over the coming decade those extra workers would add a total of $US455 billion to its economic output over that period, delivering huge additional gains for stock markets in both the world's biggest economy and around the planet.
An increase in women's labour force participation rate (LFPR) to that of other advanced countries would drive US gross domestic product (GDP) up by 0.2 per cent a year, fuelling estimated gains of 0.7 per cent a year in the S&P 500, S&P Global said in a report.
This incremental gain could add a total of $US2.87 trillion to US market capitalisation over the next decade. The current market cap of the S&P 500 is $US24.54 trillion, Reuters data show.
Because global stock markets typically take their cue from Wall Street, equities in trade-sensitive countries such as Germany, China and Korea could benefit even more from US economic expansion than the S&P 500.
US women's contribution to GDP growth would add $US5.87 trillion to global market capitalisation over the 10-year time frame, doubling the length of the current bull run.
That's around 12.9 per cent of the current market cap of MSCI's All Country World index, $US45.4 trillion.
But these figures depend on American women entering, and staying in, work.
Having been among the pioneers of women's workforce participation in the 1990s, the United States slid to 20th place among 22 advanced OECD (Organisation for Economic Co-Operation and Development) economies for women's labour force participation by 2016.
Women's LFPR in the United States reached 74 per cent in 1990 and has remained roughly stable since, while it has increased elsewhere.
"A concerted effort to increase participation and foster retention of women in the American workforce, particularly in those professions traditionally filled by men, represents a substantial opportunity for growth of the world's principal economy," the authors of the report argued.
Child care remains the biggest obstacle stopping women from fully participating in the labour force, they added, and the United States is the only OECD country that does not provide income support during maternity or parental leave by law.
"If the US were to follow the lead of many other developed countries and implement policies that encourage women to enter and remain in the workforce, the effects could reverberate globally, supporting a stock market boom far greater than the economic growth itself," they said.