Women may have come far enough in the working world that most of them now claim Social Security benefits under their own work records, rather than on their husbands’, but that doesn’t mean that they’ve really caught up.

A brief from the Center for Retirement Research at Boston College took a look at the data on the effect that lingering caregiving responsibilities — time lost from work for childbearing and child rearing — have on women. It found it takes a financial toll not just on lifetime earnings, but also on Social Security benefits.

Using the Health and Retirement Study, linked to administrative earnings records, the brief considered three questions in determining whether, and how much, motherhood might cost women in Social Security benefits.

It points out that “[i]f motherhood lowers earnings, and these losses are not made up later, then having children could give rise to a career’s worth of lower annual earnings, which would result in significantly smaller Social Security checks.”

However, most studies focus more on “reductions in women’s earnings only in the years in which their children are young,” it adds, with the result that “the extent to which motherhood is associated with lower earnings throughout [mothers’] entire working lives is not well understood.”

In addition, since Social Security does have a progressive benefit formula to compensate lower earners by allowing them to keep a higher share of their earnings the less they earn, it wasn’t known whether the motherhood penalty spilled over into Social Security benefits as well.

Researchers first looked at how much less mothers earn over their careers compared to childless women, and how much less they earn for each additional child.

The amount is substantial; lifetime earnings of mothers with one child are 28% less than the earnings of childless women, with all other factors being equal.

In addition, each additional child lowers lifetime earnings by another 3%.

Then there’s the question of how Social Security benefits differ between mothers and nonmothers.

The motherhood penalty is smaller than the earnings penalty, but mothers with one child still receive 16% less in benefits than nonmothers, and each additional child reduces benefits by another 2%.

Finally, the study looked at how each of the existing elements of the Social Security system that indirectly help mothers — the spousal benefit and the progressivity of the benefit formula — contribute to reducing the motherhood penalty.

It found that while the per-child motherhood penalty is almost negligible among women receiving spousal benefits, mothers who receive benefits on only their own earnings histories see significantly lower Social Security income than childless working women, and for each child.

It concluded that mothers end up less well off in economic terms when spousal benefits are not available, and if the receipt of spousal benefits continues its likely decline, policymakers may want to consider whether to compensate women for their lost earnings due to motherhood.