Women who have contributed to retirement savings throughout their career should have 11.2 times their final pay to meet  retirement needs, but are actually on track to accumulate only 8.6 times their final pay. That's a shortfall of 2.6 times pay. Men have a projected shortfall of only 1.9 times pay.

"Women face a number of challenges when it comes to saving for retirement including gaps in their career when they are not actively contributing to their retirement and longer life expectancies, said Patti Balthazor Björk, director of retirement research at Aon Hewitt.  "However, there are factors that women can control to boost their retirement savings, such as how much they contribute, how they invest over time and whether they keep assets within the retirement system."

Women and men take loans from their retirement savings at the same rate, but women are more likely to default on the loan if they leave their job. Seventy-one percent of women who terminated employment with an outstanding loan defaulted on the loan, compared to 64 percent of men, Aon Hewitt found.

Aon Hewitt recommends women take the following actions to build a better retirement nest egg:

• Invest more and begin investing earlier.
• Take advantage of employer matching contributions.
• Make the most of automatic features like automatic enrollment and auto escalation.
• Avoid taking loans from retirement savings.
• Take advantage of "help" tools.