In your 20s: ignoring student loan debt

Why it happens: Upon graduation, many people haven't learned how to manage their money—not because they don't get it or don't care, but because financial literacy isn't taught in school. There are so many other important things to pay for—a new car, an apartment, an interview wardrobe—and since student loans can be tricky to understand, it seems easier to push them aside.

How you can avoid it: The old rule of thumb was to "pay yourself first," but not anymore, says Cathy DeWitt Dunn, president and CEO of retirement income planning firm Annuity Watch USA. You're better off paying your loans first, since you can't get rid of them in bankruptcy court, and the fees of defaulting on a payment are astronomical—late fees can be as high as 18.5 percent of the outstanding loan, including principal and interest, according to the U.S. Department of Education. The fee is then tacked on to the principal of your existing loan.

You typically have a six-month grace period after graduation before payments kick in, but don't wait to start planning. As soon as you get out of school, ask yourself, How is your current repayment plan set up? How long do I have to repay your loans? How much is my monthly payment? If the plan doesn't work for you, look into other options. Then mark on a calendar the due date for your first loan payment and the monthly deadline for each payment, and set up bill-pay reminders.

In your 20s: being afraid of investing

Why it happens: Investing seems scary and sounds complicated, so it's no wonder so many of us avoid it altogether. Plus, people think if you don't have a lot to invest, it's not worth it. But that's not true, says Kimberly Rotter, a personal finance expert at "You can now buy and sell stock very cheaply, so the old rule to not buy stock if you can't afford 10 shares is moot."

How you can avoid it: You don't need a fancy personal finance advisor. Just call your bank—many, such as Chase, Citi, Wells Fargo, and Capital One offer investing and wealth management services—and ask how to buy a stock. It's that simple—they will help. If you'd like to read up beforehand, you can learn about the basics of investing on sites like The Motley Fool and Investopedia. And if you're still intimidated or confused by all the jargon, ask a bank representative if they have an on-staff financial advisor you can speak to free of charge. A fee-only one is legally required to put your interests first and isn't incentivized to sell you anything.

In your 20s: not learning and being proactive about finances

Why it happens: It can be intimidating to sit down and plan a budget, especially if you're iffy on the basics of money management. When you're faced with something overwhelming, apathy is a natural response. To make matters worse, many women don't consider themselves financially competent. A 2012 to 2013 Prudential study found that only one in 10 female breadwinners felt they were knowledgeable about financial products and services. Even though they made the most money in their household, they were still less likely to see themselves as the primary financial decision-makers.

How you can avoid it: The key is to make fear motivate, not debilitate, you. In reality, everyone is on the same playing field in their 20s, a time when we're all just starting out financially, says Jamal Mahmood, a certified financial planner at Access Wealth Planning. Plus, many of the decisions you make in your 20s involve a small amount of money, so it's the ideal time to make mistakes.

Start by seeing a few financial advisors—don't just follow the advice of the first one you meet. "Hearing different perspectives helps you develop your own, and you will get better at asking questions," says Mahmood. Do the same with three or four older people who you trust financially and whose experiences can help guide your own.

Still feeling shaky? Take a class that covers the basics of budgeting, retirement savings, taxes, and investing. Many local adult-learning centers offer them, says Darren Zagarola, a certified financial planner at EKS Associates, which holds a class at the Princeton Adult School. "Find one that's independently run, not sponsored by a bank or lending institution," he advises.

In your 30s: buying more house than you can afford

Why it happens: You want your first home to be your dream home, but more often than not, it won't have everything you want. A big house may make you look successful, and with a low-interest rate, buying one seems doable. But that can lead to borrowing more than you can afford long-term—it's what ultimately led to the subprime mortgage crisis and subsequent recession in 2008.

How you can avoid it: "You don't need to go out and get the house that your parents have," Zagarola says. Start small and work your way up, thinking about how you'll afford homeowner's insurance, property taxes, repairs, and maintenance, as well as how life changes—like having a baby, needing a new car, or reducing hours at work—could affect your ability to pay for it all. It's also essential to give yourself some wiggle room so that you can still do the fun stuff, such as going out to meals with friends and taking vacations.

Sure, the thought of buying a starter home and having to move again later can seem daunting, unfortunate, and just plain stressful—but it's also extremely common. The average homeowner lives in a home for seven years before moving and will move 11.7 times during her life, according to real estate site

In your 30s: competing with peers and colleagues

Why it happens: In your 30s, you start to feel more settled—you've invested in your career, your relationships are better developed, and you become curious about how you're doing. That leads to measuring yourself against everyone else.

How you can avoid it: Take a realistic look at your situation, knowing that your finances may be different because your circumstances are, says Mahmood. For example, having a young child may have prevented you from saving as much as you'd like over the past few years because so much of your money goes toward day care. Your single colleague doesn't have that expense. Avoid asking questions like, "Am I supposed to have this much in my 401(k)?" because there is no right answer. Instead of beating yourself up over how much you have saved, see where you stand financially and take small steps toward improvement.

In your 40s: thinking it's too late to start saving for retirement

Why it happens: There are any number of reasons why you may not have done the best job saving in your 20s and 30s—maybe you weren't making a steady income, you were taking care of a family member, or you were paying back debt. You can't change that, but you can work forgive yourself, figure out where you are now, and determine how to improve things from here on out.

How you can avoid it: Hitting your financial stride in your 40s and 50s isn't uncommon, because by then, you likely are making more, are further in your career, and have paid off many of your debts. That means you have more wiggle room to save for retirement. The best place to start is to take advantage of your company's matching policy by contributing the maximum they'll match. Don't have that kind of career? A traditional IRA is the equivalent of a 401(k), and while there's no matching policy, you pay taxes on your contribution later, which makes sense if you plan to withdraw the money when you're in a lower income bracket. If you'd rather pay taxes now, invest in a Roth IRA with post-tax dollars. Any profit that money accrues will remain tax-free.

"If you start saving at 40, you still have at least 20 years before you reach typical retirement age," says Mahmood. That gives you plenty of time to invest in a stock-heavy portfolio, which is riskier in the short-term, but typically offers much better returns over time—especially if you're not planning to retire in your early 60s, which today, many people don't. And to a degree, you can make up for lost time. "In and after the calendar year you turn 50, you may be eligible for catch-up contributions of up to $5,500 in an 401(k) and $1,000 in an IRA," says Simon Moore, CFO of FutureAdvisor.

In your 40s: thinking you're too old to switch careers

Why it happens: "The fear is all about the money," says Rotter. And that makes sense—taking a leap into the unknown is scary, especially when a pay cut or change in salary is involved.

How you can avoid it: Remember that your experiences have value, even if you shift your focus, says Rotter. When you enter a new field, you don't necessarily have to start at the very bottom, so long as you can sell the ways in which your carefully developed skills are an asset.

Thinking about starting your own business? If you can make more money and achieve a better balance as a consultant or freelancer, it might be a smart idea. Once you identify your strengths, weaknesses, how to compensate for the stuff you're not the best at, and your ideal client, you'll have a better idea of what you're up against. It's essential to research your preferred industry before leaving your current jobs by attending industry conferences to network and feeling out whether there's a niche you can fill that will allow you to start earning an income. If there's one thing to invest in, it's a solid internet marketing plan, including a site and social media strategy that reflects your new personal brand.

"It all comes down to is having the gumption to give it a try," says Shelley Hunter, who left her management job at a large oil company to launch Gift Card Girlfriend. "Although at times it felt like I was all over the map, I realized one day that I was gathering the skills and expertise I needed to ensure my business would really go the distance. Everybody has a unique perspective, and if you want to share yours, don't let fear hold you back."

Sarah Kaufman is the editor-in-chief of theThe Manilla Blogat, a platform that helps you manage your finances, utilities, daily deals, travel and rewards programs, and subscriptions—all in one place. She is also a regular contributor to Yahoo! Finance, The Huffington Post, Good Housekeeping, Woman's Day, The Motley Fool, and other sites.

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