The United States will soon fully understand what a millennial workforce means. The generation, which includes present-day adults aged 18 to 33, will make up some 50% of the nation's employees by 2020, according to the U.S. Bureau of Labor Statistics. And the workforce they're entering promises a much different retirement from the version their baby-boomer parents are now beginning to enjoy.

As adult millennials get their professional careers fully into gear, they face a post-recession milieu in which student loan debt, fewer matched savings plans, Social Security changes, and fears about the market brought on by the recession all pose challenges to proactive retirement planning.

So let's look at the retirement landscape for this wave of workers and discuss what they need to do to retire comfortably.

1. Millennial school debt can cut into retirement savings
The skyrocketing cost of college means that millennials graduate with an average of $29,000 in student loan debt. Paying these balances down is crucial to their ability to free up funds for retirement savings. Part of doing that is simply paying back loans aggressively -- and because you almost certainly can't save at a rate higher than student loan interest, it's important to eliminate the principal. To that end, augmenting your monthly payments can be as basic as making small changes to daily expenses. A $4 daily coffee adds up to $1,000 annually in a 50-week work year. A $10 daily lunch costs you about $2,500 annually. If you were able to cut those costs by, say, 75% -- bringing coffee and lunch from home -- you'd have an additional $2,625 per year to help pay down that $29,000.

2. Many millennials will never see a pension check
Baby boomers came up in a world that still ensured most workers a guaranteed full pension after 30-odd years of service. However, private-sector pensions are few and far between today. The millenials could be referred to as a "gig" generation; some 60% of millennial workers change jobs every 36 months or less. So, if pensions are thing of the past, what can Millennials count on to take their place?

Beyond socking away around 15% in a 401(k) or Roth IRA, one strategy is to plan for a deferred-income annuity. As a way of augmenting annual income after retirement, putting, say, $50,000 into an index fund like the SPDR Dow Jones Industrial Average -- sometime around age 45, after a millennial's career is under way -- would mean, if one started withdrawals 20 years later (assuming annual growth rate of 7% with 3% fees), a boost to annual income of some $6,000 for the next two decades.

3. For millennials, the role of Social Security will likely change
The Social Security Board of Trustees has been telling us for more than a decade that, barring a major overhaul, the trust fund on which the system in large part relies is expected to last until about the mid-2030s. After that, expectations are that benefits will be cut to the tune of about 25% per check per recipient. In other words, for every $1,000 you could anticipate right now, make that $750 if the trust runs dry. So millennials would be wise to plan for smaller Social Security benefits than the ones their parents or grandparents receive. That means shifting emphasis to savings, as we address in the next point.

4. Personal savings mean more to millennial retirees
Even the familiar 401(k) plan will prove a different instrument for many future retirees. Instead of the typical scenario that boomers enjoyed -- employers fully matching employee contributions -- percentage matches, if anything, are now more common. Therefore millennials will carry more, if not all, of the responsibility for growing their retirement savings. Given all the other factors at play, it's best to start contributing at least 10% of your pay to a retirement plan and then push for 15% or more whenever possible. Think about it: With a $40,000 annual salary, that would be $4,000-$6,000 of tax-free savings per year. Do that for 40 years, and with a reasonable 7% return on your money, you'll have tucked away $828,000-$1.2 million for retirement.  

5. Millennials must work to overcome market fears
It's not hard to understand why millennials might be a bit wary of the stock market. Financial advisors speak about the effects of recent history. "Millennials have witnessed two significant market events in the past 14 years -- the 2000 tech-bubble collapse and the 2008 financial crises," says James A. Daniel, a registered financial advisor for The Advisory Firm, in an email interview. "Having witnessed this, it is easy to have a jaded view of investing and the markets. Overcoming this psychological barrier and learning to invest for long-term goals is a major challenge."

And this is a challenge that millennials have to face. Retirement is almost always deeply dependent upon investing --and doing so wisely, taking on some risk to achieve returns. Reaching out to advisors can help, revisiting the stock market as it is today with expert advice that can help dispel fears based on the past.

Finally, there is another characteristic about the financially minded millennials to consider: They're often entrepreneurs. According to the U.S. Chamber of Commerce Foundation, 29% of all entrepreneurs, as of 2011, were 20-34 years old. Millennials launched nearly 160,000 start-ups each month, by the Foundation's numbers. 

"They are spending their savings, investing in their business ventures instead of saving it for retirement," said Parker Harris, social entrepreneur, millennial consultant, and co-founder of Junto Global, in an interview by email. "The Millennial dream is to start their own company and have it bought out by investors -- providing them the cash for an early retirement."

Of course, such an accomplishment would solve many retirement-planning problems for a generation on whom a greater burden has been placed. But it won't negate the underlying need to manage retirement resources so that they provide the greatest benefit. Proactive saving, savvy approaches to investment, and a set of strategies that emphasize self-reliance are still the roadmap for the coming journey of millennial retirees.

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