Numerous studies have shown balancing the gender scales doesn’t just help women—it helps the economy, too. A new report from the McKinsey Global Institute offers a new eye-popping estimate of that untapped potential.

The report, released Thursday, found that achieving parity for women–that is, if women played an identical role in the economy as men–could boost annual global gross domestic product by as much as $28 trillion in 2025, or 26% of global GDP, compared with a scenario in which nothing changed.

That’s about as big as the combined economies of the U.S. and China, and is twice what previous studies have estimated, the authors said.

The report looked at gender quality indicators—from women’s labor-force participation rates to maternal mortality to financial inclusion—in 95 countries, which account for about 90% of the world’s GDP and its population of women.

Even just narrowing the gender gap could add significantly to global economic output. If each country surveyed advanced gender equality by matching the rate of improvement of the best-performing country in their region, it could boost growth by $12 trillion in 2025, the study found.

“It’s a prize worth chasing,” said Anu Madgavkar, one of the study’s authors.

Increasing women’s participation in the labor force would provide the biggest boost to GDP—about half—as well as closing the gap between the number of hours worked by women and men and shifting women into higher productivity sectors.

The highest potential economic benefit would be in India, along with the rest of South Asia and the Middle East and North Africa, which received some of the lowest marks for gender equality in the McKinsey study.

But both advanced and emerging economies stand to gain. The study found that 74 of the 95 countries analyzed could boost GDP by more than 20% in 2025 if women were able to reach their full economic potential.

In the U.S., for example, gender parity could add $4.3 trillion, or 19%, to U.S. GDP growth in 2025. Even if the U.S. only matched the rate of improvement of Spain, the best-performing country in the region, GDP could grow as much as $2.7 trillion, or 12%, the report found. (For purposes of the study, the U.S. belongs to a region that includes Western Europe.)

McKinsey researchers found that progress in four key areas would have the biggest impact: closing gaps in education, closing gaps in financial and digital inclusion, bolstering legal protections for women and improving attitudes and practices toward unpaid work, such as household work and caring for family members.

“Businesses can find many ways in their own self-interest that make business sense to actually work with the government or the social sector to make a difference, not just in their own workplaces but beyond,” Ms. Madgavkar said.

A slew of studies have shown that breaking down barriers to women can help spur economic growth. That’s especially critical now as global growth appears to be slowing, and central banks have fewer policy tools to stimulate their economies.

“Women’s empowerment is not just a fundamentally moral cause, it is also an absolute economic no-brainer,” Christine Lagarde, managing director at the International Monetary Fund, said in a keynote speech at the W-20, an ancillary conference launched by the Group of 20 largest economies aimed at boosting gender parity in the global workforce.

“It holds the potential to boost growth, raise overall per capita income, tackle poverty and reduce income inequality for people all over the world,” the IMF chief said.

A report from the World Bank released earlier this month found that about 90% of countries around the world have some form of legal discrimination against women, many of which prevent them from joining or participating fully in the economy.