Women have made significant inroads into the workforce over the past few decades, increasing levels of labor participation, education, and share of earnings. But an income gap lingers, and not just between women and their male peers.

Working women today earn more than their mothers did, on average, but they still make less than their fathers did at similar stages in their lives, according to a study released Tuesday by Pew Charitable Trusts tracking female economic mobility across generations. The study compares women who entered their “prime working years” (approximately 40 years old) in the 1970s with their daughters, who reached 40 in the early 2000s, by measuring participation rates, hours worked, and wages earned.

Unsurprisingly, the “daughters” in the study worked more hours and had higher wages than the “mothers” – the latter group worked an average of 24 hours a week and earned about $10 an hour. The daughters worked 34 hours a week at an average of $19 per hour, which translated to three times more earnings than their mothers.

The explanation is fairly simple: more women, including mothers, are working these days. Only 53 percent of the mothers surveyed earned wages between 1972 and 1986, compared with 85 percent of the daughters.

Likewise, 85 percent of the working daughters in the study earned more than their actual mothers. But less than half earned higher wages than their fathers during their prime working years.

The gap grows more pronounced with wealth – among the highest earners, only 21 percent of women earned more than their dads. By comparison, 70 percent of sons had higher hourly wages than fathers, and 63 percent of the highest earnings group made more.

“At every rung of the economic ladder, women’s median wages rose by 50 percent or more, but daughters continue to earn lower hourly wages than fathers did on the same rung,” the study reads. “Daughters working full time contribute more than half of family incomes, strengthening financial security. The extent of this contribution, however, varies based on family structure: Daughters who are in a couple (either married or cohabiting) supply 45 percent.”

Given a persistent wage gap (full-time female workers earn about 77 cents for every dollar a man earns) and many of the roadblocks that still exist for working women and especially mothers, the finding isn’t a huge shock.

Women are underpaid relative to men even in fields like medicine, and there are differences in labor force participation during peak childbearing years.  Fathers get a wage premium, while employers are less likely to hire mothers. And reports say that a majority of mothers are working, but we don’t have adequate childcare. All of this puts women in a secondary labor market.

Even high-achieving women have a tendency to make their husband’s careers a higher priority, not because they want to but purely for economic reasons. Men often have better earning potential to begin with, so it becomes a self-fulfilling prophecy.

Still, the Pew study and others note that women have more of a bearing than ever on a household’s economic mobility. 40 percent of American mothers, including single moms, are now the primary breadwinners for their families, up from 11 percent in 1960.  Significant changes are still needed for income equality.