While women globally have positive expectations about their future retirement, there are also dark storm clouds threatening their retirement readiness.

A report from the Transamerica Center for Retirement Studies (TCRS) in collaboration with Aegon, Women: Balancing Family, Career & Financial Security, finds that one of the greatest issues facing women globally is an imminent retirement savings shortfall. Only 20% of women believe they are on track to meet their income needs when they retire, and 40% don’t know.

Read: Fewer women say they’re ready for retirement

“Most women are saving for retirement; however, they are not saving enough to meet their future retirement income needs,” says Catherine Collinson, president of TCRS. The survey finds that the majority (57%) of women are saving for retirement, including 36% who always make sure they are saving and 21% who save only occasionally. Another 24% are not saving but intend to do so.

While most women are saving, few women globally (10%) say they are saving enough for retirement, and almost one-quarter (23%) indicate that they are hardly saving at all.

Read: Women more likely to outlive retirement savings

“When comparing a woman’s ability to save to that of a man, her life’s circumstances, which may include lower pay and/or time out of the workforce, make it very difficult for her to save consistently and adequately,” he adds. Globally, the survey finds that women’s annual income is about 27% less than what men earn.

Fewer women (38%) are offered a retirement plan with employer contributions compared with 45% of men. In cases where savings plans require full-time employment or an eligibility waiting period, many women may be effectively excluded from participation.

“Given current employment trends, it’s no wonder that women are struggling to adequately save and financially prepare for retirement,” says Collinson. Overall, 67% of women say that a lack of money to invest is an obstacle to saving.

Read: Women less confident about retirement saving: Study