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Women make less money than men -- about $0.78 per every $1 men earn on average, according to the U.S. Census Bureau -- and that disparity can follow them into retirement, leaving them struggling to get by in their golden years.

According to the Center for Financial Literacy at Boston College, a widow needs about 75% of a couple's pre-retirement income to maintain the lifestyle she had before her spouse died, but widows have on average about 60% of the couple's income. This is troubling, given that a recent report from the Federal Interagency Forum on Aging found that women aged 65 and older are nearly three times as likely to be widowed as their male counterparts.

With more women going it alone in retirement, it's especially important that they take charge of their finances before they reach retirement age. This holds particularly true for women who don't have, or perhaps don't want, a spouse to rely on for financial support.

The good news is that this is a solvable problem. Women in their forties and fifties can still close the gap if they act now. Here are three ways women can increase their retirement income while improving their opportunities to enjoy life later on.

Lean in

In her groundbreaking 2013 book Lean In: Women, Work and the Will to Lead, author and Facebook chief operating officer Sheryl Sandberg encouraged women to be more aggressive in seeking raises and leadership positions at work. Part of the reason for the wage gap, she writes, is that women unintentionally hold themselves back by underestimating their abilities and failing to negotiate for themselves.

Sandberg has a point: If you don't ask for a promotion, bonus, or raise, then you may never get one. But you can't expect to receive that raise without making sure you've done everything possible to be a valuable employee. Take on challenging projects, particularly when other employees shy away from them. At the very least, you'll learn something new and expand your skill set. Don't be afraid to speak up when you have an idea that will benefit the company -- and be prepared to put that idea into action if it's accepted. No matter the task, give it your all.

This could mean putting in some long hours, but when the time comes to negotiate that raise, you'll have plenty of evidence to prove that you deserve it. If possible, quantify your accomplishments -- for example, show exactly how you boosted sales by 15% or stayed $10,000 under budget on a project. And don't be afraid to recite your qualifications and achievements point by point.

If all of this doesn't get you the recognition you deserve, then you'll still have new skills and experience that will help you negotiate a better position with a new employer. And if you receive a competing offer but don't necessarily want to leave, then you can give your current employer a chance to make a counteroffer. Faced with the prospect of losing a valuable employee, your employer may finally recognize your worth.

The benefits of seeking getting a raise are twofold: You can sock away that extra money to fatten your retirement savings, and you can also increase the size of your Social Security retirement benefits, which are based on your past earning.

Work longer, work harder

Even if you get that promotion, you should consider getting a part-time job if possible. This can work for you in a variety of ways. Not only can it help you save more for retirement, but it could also help you get a handle on your second act in life.

More than 63% of people plan on working while retired. So before you clock out of your day job for good, try a second job to figure out what sort of part-time work you might want to do in retirement. Make it a job you enjoy, because one of the best reasons to work part-time during retirement is to stay active without suffering undue stress. For example, you might consider taking on a second job as a baker, a craftsman, or some other profession you've been dying to explore but simply put off because you were building a career.

Volunteer to help others -- and yourself

It's no secret that doing good for others can impact your own life in positive ways. Whether or not you wind up with a fat raise or a second job, consider volunteering as a way to develop new interests and network with like-minded people.

For example, museums and theaters provide tons of opportunities for volunteers to soak up culture for free while building new skill sets and developing relationships that can lead to work. Serving up lunch at a soup kitchen can turn into a second meaningful career in social work. Being a literacy volunteer for school children could lead to a job as a tutor.

Whether or not you wind up with a job, volunteering feels good. Studies have shown that older adults who volunteer reap health benefits such as lower hypertension and better cognitive function. Volunteering also promotes higher self-esteem and a longer life expectancy. In short, volunteering can lead to a positive mindset that can help you figure out how to tackle your next financial goal.

For many women, saving enough money can mean the difference between a vibrant retirement and a continuous struggle to make ends meet. By taking these steps now, they can begin to close the retirement savings gap.