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 norms that 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 this 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

From the moment an infant is born, the brain begins to form one million new neural connections per second through experience, their environment, and warm, responsive interactions with adults, building the architecture of all future learning, behavior, and health. At two months, infants begin to smile and recognize caregivers’ faces. At four months, they can hold their heads up unsupported. By six months, infants have begun to form healthy or unhealthy attachment patterns to caregivers, based on the quality of the caregivers’ responsiveness, which research has found is an important predictor of a child’s future academic, social, and emotional success and wellbeing.

While some studies show limited links between extending leave and improved child health, other studies have found that supporting families in the early years with an adequate duration of paid family leave can contribute to fewer low birth weight and early term babies, particularly for children of single and African American mothers, fewer infant deaths, higher rates of breastfeeding, well-baby care and immunizations, longer parental lifespan, improved mental health, and increased long-term achievement for children.

“The relatively consistent findings about paid leave predicting increased birth weight and fewer preterm babies is somewhat puzzling, given that the leave is usually taken post birth,” said Taryn Morrissey, public policy professor at American University and author of Cradle to Kindergarten: A New Plan to Combat Inequality. “But it may be that pregnant mothers experience less stress when they don't have to worry about what will happen economically or to their children post birth.”

• Infant mortality: The U.S. has one of the highest rates of infant mortality and SIDS deaths of all advanced economies. A seminal study of paid leave duration and health outcomes in 16 European countries from 1969 to 1994 found that a 10-week extension of paid parental leave reduced post neonatal infant mortality (28 days after birth) by 2 to 3 percent, and child fatalities by 1 percent. Job-protected paid leave of 40 weeks showed the greatest reduction to mortality. Another study of 20 low- and middle-income countries found an even greater impact: each month of paid maternity leave was associated with a 13 percent decrease in infant mortality. The benefits of unpaid, leave, however, are not equally shared. One 2011 study of the Family Medical Leave Act in the United States found unpaid leave is associated with small increases in birth weight, decreases in premature births, and a substantial decrease in infant mortality, but only for college-educated married mothers, presumably because lower-educated and single mothers are unable to afford unpaid leave.
• Long-term achievement: Researchers have been following the lives of Norwegian children who were born before 1977, when mothers were entitled to 12 weeks of unpaid leave, and children born after 1977, when a new law guaranteed mothers an additional four months of paid leave. The longer paid leaves led to a 2.7 percent decline in high school dropout rates and a 5 percent increase in wages at age 30, with positive outcomes even greater for those whose mothers were less educated.
• Child maltreatment: A study of hospitalizations due to abusive head trauma, the chief cause of deaths from child abuse, found a significant decrease among children younger than two after California’s six week paid family leave law went into effect in 2004.
• Chronically sick children: Children who have special health care needs make up 13 to 17 percent of the child population in the U.S. One study found that the longer the leave, the more parents felt that time benefited their child’s physical and emotional health. Longer unpaid leaves, however, were also associated with greater reported financial problems and perceived negative job performance.

Childbirth in the United States is hazardous to women’s health. While rates of maternal mortality have been falling in other advanced economies, the rate of women dying in childbirth in the United States increased, from 12 to 14 per 100,000 births, between 1990 and 2015, a rate higher than in Bosnia, Libya, and Kazakhstan. And once mothers give birth, an estimated 10 to 15 percent will experience postpartum depression.

The research, what little there is, on how the length of paid leave affects maternal health shows positive effects on mental and physical health. The question is difficult to study in the U.S., largely because there is little paid leave and little variation in leave: Most first time mothers in the United States return to work within 12 weeks, the time allotted by the unpaid Family Medical Leave Act. But rigorous U.S. and international studies find that adequate periods of paid leave have significant, positive effects on maternal physical and mental health, an increase in breastfeeding, which has health benefits for mother and child, and a reduction in maternal stress and intimate partner violence. Leaves of fewer than 12 weeks have been associated with higher maternal depression and anxiety, reduced sensitivity to the infant and knowledge of infant development, negative impact on self-esteem, work stress and overload, and marital dissatisfaction.

• Psychological distress: A 2013 longitudinal study of Australian two-parent families found that the length of a mother’s leave after childbirth affected her mental health, the quality of parenting, and couple relationships. Psychological distress was significantly less likely among mothers who took more than 13 weeks of paid leave or 26 to 52 weeks in total. Leaves longer than 26 weeks, however, were associated with “distant” parenting. Mothers who experienced workplace problems during pregnancy were also more likely to report feeling rushed and their couple relationship as “unhappy” or “argumentative” two to three years later.
• Physical health: Although state, employer, and private temporary disability insurance typically cover up to six weeks for a woman to recover from a vaginal birth and eight weeks from a Cesarean section, (C-sections make up about one-third of all U.S. births) a Minnesota study following more than 400 mothers for 12 months after childbirth found that women had a number of physical symptoms and illnesses that persisted long after six weeks, including respiratory symptoms, dizziness, hot flashes, hemorrhoids, constipation, fatigue, sexual concerns, and hair loss. An Australian study found that 94 percent of new mothers reported one or more health problem six months after childbirth. Yet women underreport these issues—more than a quarter reported they hadn’t talked to a health professional.
• Mental health: Researchers assume that since the stress of juggling childbirth, recovery, caregiving, and professional work are likely greater than a mother's ability to cope, she’s at a higher risk for depression. As a result, taking an adequate amount of paid time off may help mothers to physically recover from childbirth and adjust to new caregiving and professional responsibilities. One study found increasing the length of maternity leave from under eight weeks to eight to 12 weeks showed the biggest improvement in mental health, and that increasing the length of leave by one week could reduce depressive symptoms by 6 to 7 percent.

Longer paid leaves also have long-term benefits. Another U.S. study found that increased length of paid leave is associated with decreased depressive symptoms until six months after childbirth. Using European data, one long-term study found that longer maternity leaves are associated with greater mental health years later in old age.

Just as women’s roles have expanded in recent decades beyond caregiving in the private sphere into the public sphere of work, men’s roles as caregivers have been evolving as well. A recent survey by the Pew Research Center found that a majority of Americans support not just paid maternity leave, but paid paternity leave, though support is much stronger among younger Americans than those over 65, by 82 to 55 percent. And 71 percent say it’s important for new babies to have equal bonding time with their mothers and fathers.

Yet the median length of leave for fathers in the U.S. is about one week (compared to 11 weeks for mothers). Seven in 10 men reported taking two weeks or less off work after the birth or adoption of a child. Nearly two-thirds wished they’d had more time. As many as 20 percentof U.S. companies do not comply with the Family Medical Leave Act and offer leave to fathers, compared to 7 percent for mothers. Internationally, 70 countries provide paid paternity or shared parental leave. Paid leave for men averages just over eight weeks in OECD member states, with 13 countries reserving three months or more for fathers. Japan and Korea reserve as much as 12 months.

Although there is little research on the caregiving experience of men, the length of paid leave and its impacts, some studies have found that men taking caregiving leave of adequate duration and wage replacement is associated with reduced family stress, improved gender equality,and more involved parenting, which can lead to better social, emotional, cognitive and health outcomes for children, as well as healthier, more stable relationships with partners.

• Paternal health: One quantitative survey in Sweden found that men who were on parental leave for 30 to 60 days had a 25 percent reduced mortality risk compared to men who did not take leave. However, men with more education, status, and income—factors that are often associated with better health—also tend to take longer paid leaves than working class men.
• Involved fathering: Studies in Iceland, where in 2012, 92 percent of fathers took paid parental leave lasting an average of 87 days, found that the longer fathers are on leave, the more likely they are to say they have a better understanding of a child’s needs and how much work it is to care for a child, and that their enjoyment of caring for, their emotional attachment to and participation in the caring for a child increases in the short and long term. Other studies have found that when fathers take leaves of two weeks or more, they’re more likely to be involved in direct child care nine months after birth, and more hands-on throughout a child’s life
• Gender equality: The wage gap noticeably widens when women have children, as policy, workplace practice, and traditional gender expectations of the male breadwinner and female caregiver lead to women being primarily responsible for housework and child care, even when working full time—what sociologist Arlie Hochschild called the “second shift.” Research suggests that the ability for women to return to work after having a child at the same wage, as well as not losing income during time off, could help close the gap. A 2016 analysis suggests New Jersey’s state paid leave policy has helped close its gender wage gap between women and men. When men take leave, women are not only more likely to return to work, but earn more. One study in Sweden found that every month a father stays on paid parental leave has a larger positive effect on a mother’s earnings than if she’d reduced her leave by the same amount.

When countries initially expanded maternity leave to include parental leave or paternity leave, few men took paternity leave and women tended to take all parental leave, further reinforcing traditional gender roles. Studies, particularly in Iceland and Quebec, which have “use it or lose it“ paid leave “daddy quotas” for men—12 weeks in Iceland, 5 weeks in Quebec—suggest that policies that provide adequate wage replacement and actively encourage men to take longer leaves disrupt traditional norms and lead to greater gender equality at work and at home in the long run. For instance, in Iceland, before the “daddy quota,” mothers did the majority of child care at a child’s birth, and were still doing the bulk of the caring when the child turned three. After the quota, 70 percent of married and cohabiting couples were equally sharing child care by the child’s third year.

Beyond the wage gap, research has found that mothers suffer additional penalties in the workplace: simply becoming a mother changes assumptions others have regarding her commitment and even competence. That could change, Taryn Morrissey argues, “if both mothers and fathers took paid leave and were viewed as being equally committed to family, and work.”

Employers providing paid family leave report that it’s both good for their workers and good for their businesses: Morale is higher, productivity increases, and the company is better able to attract talent and engage and retain employees. A 2017 Ernst and Young survey found more than 90 percent of companies with paid family leave policies reported either a positive or neutral effect on morale, profitability, and productivity.

Research shows that disadvantaged workers are less likely to afford to take unpaid family leave. Paid family leaves of adequate duration, however, have been found to help close the gender pay gap, reduce family reliance on public assistance, and boost women’s return to work.

• Women in the Workforce: Women’s labor force participation has been dropping steadily since 2000, and one study found that a lack of paid leave and family-supportive policies are important reasons why. Policies to support gender parity in the U.S. workforce could add up to $4.3 trillion to the economy by 2025. One study found that women who take paid leave are 93 percent more likely to be in the workforce 9 to 12 months after a child’s birth than women who take no leave, and another that mothers who took paid family leave increased their work hours, and likely their wages, by 10 to 17 percent one to three years later. Duration of leave matters. Like a bell curve, paid leaves that are too short push women out of the workforce. Yet when leaves are too long, women can have a hard time getting back in, according to one study in the Czech Republic, where paid maternity and parental leavecan last until a child’s third birthday. While there’s some debate, research finds that the optimal duration of paid leave for women’s return to work without severe penalty is nine months to one year.
• Productivity: Workplaces with family-supportive policies are more productive. One survey of more than 2,000 U.K. workplaces found that those with parental leave policies are 60 percent more likely to report above-average financial performance than companies without such policies. For workplaces with paternity leave policies, it’s 93 percent, compared to those without it. One study of OECD countries found that unpaid leave is only linked to higher productivity when paid maternity leave is short or not available, as in the United States. If the U.S. were to adopt a paid maternity leave policy at the average OECD level of 15 weeks, the researchers predicted a productivity increase of 1.1 percent over time. Studies of the California, New Jersey, and Rhode Island state paid family leave systems found a majority of companies reporting positive or neutral effects on productivity.
• Employee retention: When Google extended its paid leave from 12 weeks to 18 weeks, attrition among young mothers dropped by 50 percent. When Accenture extended its paid maternity leave from 8 weeks to 16 weeks, attrition among mothers dropped by 40 percent. And when Aetna expanded its maternity leave, the share of women returning to work jumped from 77 to 91 percent. Higher retention benefits hold true for low-wage workers as well.