Babies are a lot of work, as new parents quickly discover. Newborns need feeding, changing, bathing, holding, and help getting to sleep. The work of parenting, however, does not rest evenly on mothers' and fathers' shoulders, a new study finds.

When researchers asked working parents how much their daily workload had increased with the arrival of their first child, both men and women estimated it had grown by over four hours each day. But when the same parents kept daily diaries of how they spent their time before and after the baby was born, a different picture emerged.

These are the couples you would expect to have the most egalitarian relationships…But that's not what we found.

Both parents seriously overestimated the amount of time their babies added to their workloads, but men were especially off — the time diaries showed women's workloads increased by two hours a day, while men's total working time each day increased by only about 40 minutes.

Uh-oh.

What's interesting is that before the baby came, couples shared housework equally. “The birth of the child dramatically changed the division of labor in these couples. What was once a relatively even division of household work no longer looked that way,” Jill Yavorsky, co-author of the study, said in a statement.

The couples in the study aren't exactly average U.S. couples. They were part of The New Parents Project, a long-term study of dual-earner couples' adjustment to first-time parenthood. Not only do both spouses have jobs, they tend to have higher-than-average levels of education. Both parents had reported they planned to keep working after their child was born.

“These are the couples you would expect to have the most egalitarian relationships,” said co-author Claire Kamp Dush, an associate professor of human sciences at The Ohio State University. “They have the education, the financial resources and the other factors that researchers have believed would lead to equal sharing of responsibilities. But that's not what we found.”

Working with Sarah Schoppe-Sullivan, a professor of human sciences at Ohio State, the researchers had couples complete time diaries twice, once during the third trimester of pregnancy and then again when their babies were about 9 months old.

At both times mothers and fathers each provided a detailed accounting of their time for one workday and one non-workday. They recorded all their activities on paper, beginning at 4 a.m. and ending 24 hours later. They included any simultaneous activities they did while multitasking.

Both men and women reported doing about 15 hours of housework per week, as well as 42 to 45 hours of paid work. And when asked during pregnancy, nearly all of them agreed that each should share child care equally.

But the time diaries after the baby arrived indicated that men did about 10 hours a week of things like changing diapers and bathing the baby. Women did 15 hours per week.

The time diaries showed a similar gender gap when it came to tasks like reading to the baby and playing. Men spent about four hours per week in these child engagement tasks, while women spent about six hours.

Both men and women overestimated how much time they spent on housework. Men's estimates of housework differed sharply from what they recorded in their time diaries. The diaries revealed that on average the men did 9 hours of housework a week — one-fourth as much as the 35 hours they thought they were putting in. Women put in 13.5 hours doing housework — 14 hours less than they thought they were doing.

Were women doing more childcare because they clocked fewer hours at their paid jobs? No, at nine months, according to the study results, both men and women were still working the same number of hours.

“A lot of data shows that many women eventually decrease their time spent at paid work after having children, but we don't know when it happens,” Yavorsky said. “This study shows that they're not doing it right after the birth of their first child.”

Kamp Dush added, “…[T]he key is that this new routine seems to be that the woman is doing more of the housework and more of the child care, while not doing any less paid work.”

The reasons for the change are complex and not entirely the fault of mothers or fathers. Other research led by Schoppe-Sullivan has found that some mothers control how much fathers are involved in childcare and what they can do, bringing on some of the inequities themselves.

“Women shouldn't try to manage their partner's parenting. But men also need to take the initiative and learn child care duties that their own socialization may have neglected,” said Kamp Dush.

That means fathers need to realize they can — and should — pick up the baby without being asked; change his or her diaper rather than leaving it to mom. Dads may not be able to breastfeed, but when infants start on solids, they can spoon food just as easily as a mother can. New mothers need to let go a little and not feel they have to be the sole parent in charge.

The study will be published in the June 2015 issue of the Journal of Marriage and Family and was presented at the Council on Contemporary Families' Symposium on Housework, Gender and Parenthood.