The United States remains one of the few countries on earth—along with Papua New Guinea, Suriname, and Tonga—with no national paid family leave policy, despite the fact that a majority of women and mothers work outside the home, that a majority of children are being raised in families where all parents work, and that an aging population is increasing caregiving demands on working age men and women.

With families under intensifying time pressure and stress, growing economic inequality, and widespread public support for paid family leave, more policymakers on the federal and state level and individual companies and organizations are grappling with how to craft paid family and medical leave policies that will support individuals and families, and work for businesses and the economy.

But how long should those leaves last? How much time is enough? And for whom?

Lengths of paid family leave vary wildly around the globe, from a few days to, with home care leaves, a few years. Some of the earliest policies—Germany was the first to enact paid maternity leave in 1883, followed by Sweden in 1891, and France in 1929—initially granted lengthy paid leave after the birth of a child to women, not men. That served to reinforce traditional gender normsthat men are breadwinners and women caregivers, intensified women’s exhausting unequal “second shift” of housework and child care after a full day of work, and exacerbated poor health, family strife, and unequal pay.

Beginning in the 1990s, a majority of countries in the Organization for Economic Cooperation and Development (OECD) began offering job-protected parental leave and paid leave specifically to fathers, some with “use it or lose it” provisions and higher wage replacement to encourage men to take an active role in caregiving and promote gender equality at work and home.

Now, the length of paid leave for new and adoptive mothers in OECD countries averages 18 weeks, with some countries, like Bulgaria and the U.K., offering close to one year. For fathers, the average is eight weeks, with Japan and South Korea offering up to one year.

In the United States, the 1978 Pregnancy Discrimination Act enabled some women to apply for six to eight weeks of partially paid disability pay for medical reasons. That only applied to women who lived in five states with Temporary Disability Insurance programs, who worked for employers offering it, or who bought their own private insurance. While six to eight weeks was, at the time, considered the length of time mothers needed to recover physically from childbirth, subsequent research shows that physical illness, post-partum depression and symptoms such as fatigue, pain, and dizziness can last far longer.

The United States offers 12 weeks of unpaid leave under the 1993 Family Medical Leave Act. It covers just 60 percent of the workforce, because the law applies only to full-time workers who’ve worked at least 1,250 hours in the previous year at firms with more than 50 employees. Rather than being based on scientific evidence, 12 weeks represents political compromise. Early backers of the bill – which took nearly ten years to pass and was twice vetoed by President George H.W. Bush – pushed for six months of paid leave, which was eventually whittled back to 12 weeks of unpaid leave. Critics derided the bill as a “yuppie entitlement.” Subsequent research has shown, indeed, that women from disadvantaged backgrounds are far less likely to have access to paid leave and can’t afford unpaid leave.

Businesses and organizations currently voluntarily offer paid family leave to 14 percent of the civilian workforce, generally highly skilled workers. Workers with the highest incomes are three and a half times more likely to have access to paid family leave than those with the lowest incomes. And while unpaid FMLA has led to substantial reductions in infant mortality and other benefits, research shows that that’s largely true for college-educated married mothers who are better able to afford unpaid leave.

Political considerations, not science, also shaped state paid leave policies. A handful of  states offer extended lengths of unpaid family leave beyond the FMLA. An even smaller number offer paid family leave. California and New Jersey offer six weeks and Rhode Island four weeks of paid leave, in addition to six to eight weeks of paid temporary disability insurance for women. The paid leaves are part of statewide Temporary Disability Insurance programs, which are funded through a payroll tax on employees. Rhode Island is the only state to offer job-protected paid leave. To get that, backers of the bill had to agree to shave the original eight-week proposal down to four. “As with all things political, you have to start incrementally, with what already exists,” said Gayle Goldin, the Rhode Island state senator who sponsored the paid leave bill. “That doesn’t mean that the length of leave is tied to a medical standard or best practice.”

There are host of factors that make measuring the optimal duration of paid leave difficult. And some studies are not designed well or the results are inconclusive. Some questions are understudied, particularly when it comes to men, and paid leaves to care for oneself, or sick or elderly family members. Yet a growing body of research is finding that, on the whole, job-protected paid family leaves of adequate duration and wage replacement lead to more income and gender equality, significant reductions in infant, maternal and even paternal mortality, improved physical and mental health for children and parents, greater family stability and economic security, business productivity, and economic growth. 

The improved child and parent physical and mental health may be due not only to families’ ability to take more time to recover, bond, breastfeed and go to doctor appointments, but also to increased family economic security, both via paid time off and because paid leave has been shown to increase the likelihood of women returning to work.

Further, in many OECD nations, paid family leave is followed by high-quality, subsidized child care systems starting at age one, which better enable families to combine work and home responsibilities. The United States has no such system: Parents bear the majority of the cost of care. The cost of infant care outstrips the cost of in-state college tuition in 33 states and eats up as much as 25 percent of the median household’s income. Caregivers earn poverty wages. And quality, particularly for infants, is mediocre at best. The National Association for the Education of Young Children recommends one caregiver take care of no more than 3 or 4 infants for safety and quality. Only 35 states and the Department of Defense meet that standard for child care centers. Only 16 states and DOD meet the standard for family child care homes. 

“Honestly, based on the evidence related to child health and development, there is a good case for a year of paid leave so that parents can bond with their children, arrange quality child care, and take their children to the doctor for all their well-baby visits and immunizations, and so that mothers can breastfeed for a sustained period of time,” said Jane Waldfogel, professor of social work and public affairs at Columbia University’s School of Social Work, who has extensively studied paid and unpaid leave around the world.

Christopher Ruhm, professor of public policy and economics at the University of Virginia, who, too, has spent much of his career studying family leave, is pragmatic. “If I had my druthers, what we would do right now is switch FMLA from 12 weeks unpaid to paid, with a specific plan to evaluate it in five years,” he said. “The reason I wouldn’t go longer is that the U.S. is different from other countries, and we’re not sure of the impact. So I would start small. Because frankly, I want it to succeed.” 

In our latest Better Life Lab project, we scan some of the best U.S. and international research to lay out how the length of paid family leave impacts four areas: infant and child health and wellbeing, maternal health and wellbeing, gender equality, and businesses and the economy. While this project focuses primarily on paid parental leave, more research is needed to gauge the optimal duration of paid family leave to care for sick or aging family members or oneself. 

Optimal Paid Leave Duration Recommendations:

• Infant and child health and wellbeing: One year, split between parents

• Maternal health and wellbeing: Six months

• Gender Equality: Equal bonding leave time, continuous or intermittent, with policy and culture support for men to use leave

• Economic Impact: Nine months to one year for women’s labor force participation, with graduated return to flexible work