Look forward retirement payday - retirement written in calendar and highlighter (iStock)

If it were completely based on discipline, women would be way ahead of men when it comes to retirement savings.

Not only are women more likely to save in retirement plans than men are, but they also save more and are just as aggressive with their cash as their male peers, according to a new report from Vanguard. Take a look at the numbers:

Women were more likely to participate in their retirement plans at work than men, with 73 percent of all women studied participating in plans, compared to 66 percent of men. And that held true for every income level.

Participation rate in retirement plans in 2014, by income and gender. (Courtesy of Vanguard )

When they did save, women were also likely to put away a bigger share of their pay. Overall, the women studied saved 7 percent of their salary in retirement savings accounts, compared to the 6.8 percent of pay saved by men. Saving rates increased with earnings, but at every income level, women saved a higher share of their pay than men did.

“Women seem to be a bit better at this than men,” says Jean Young, senior research analyst at Vanguard and author of the report. “They’re more likely to save and when they save, they save more.”

Percent of pay saved in retirement plans in 2014, by income and gender. (Courtesy of Vanguard )

Women were just as likely as men to invest in stocks, with 73 percent of their savings invested in equities, compared to 74 percent for men. And women were more likely to use investing vehicles like target-date funds, which adjust portfolios automatically as a person reaches retirement age. That in turn makes them less likely to trade within their retirement accounts, a habit that research shows can boost long-term returns by minimizing the chance that investors will try to time the market.

But women still fall woefully short when it comes to one key measure: their account balances. Women held an average $79,572 in defined contribution plans in March, compared to the average $123,262 held by men, according to Vanguard. The median account balance for women was $24,446, compared to $36,875 for men.

So what is behind the gap?

Don’t blame it on shoes. The bottom line is that men make more money than women do, on average, and that makes it easier for them to save more money over time, says Young. Indeed, when Vanguard researchers took income into account, the savings gap nearly vanished, except for people at the very high end of the income spectrum. As the chart shows, the gap even disappears in some cases when men and women earn the same level income.

Median retirement savings by income (in thousands). Women (blue) had median account balances that were similar to men (green) at most income levels, except at the higher end. (Courtesy of Vanguard)

The exception for higher earners is likely explained by the fact that men have slightly longer tenure in higher paying jobs than women did, Young says, giving them more years to save. (And that affects a small group of savers, since only 1 percent of women and 2 percent of men studied earned more than $250,000 a year.)

Some women may also be held back by an obstacle not fully covered in this report: access. Lower-income workers, and people who work part time, are less likely to have access to a retirement plan at work, according to the Bureau of Labor Statistics. Those are often the types of jobs that are more likely to be held by women, says Craig Copeland, a senior research associate for the Employee Benefits Research Institute, which has studied the gender gap in IRA balances.

The gender pay gap can also be explained in part by trends in job selection, Young says. But for women, the findings are another reminder to negotiate pay when applying for jobs or promotions. The pay gap can have an effect, even long after you’ve stopped working.

Read more:

Why the retirement savings crisis is also a women’s crisis

Always negotiate pay — even on your first job out of college

What you need to know about the lucrative Social Security strategy that’s going away

The inequality in retirement savings between top 100 CEOs and U.S. workers