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The main goal of retirement planning is to be able to maintain roughly the same standard of living after your career as during it. But achieving that goal can a challenge. For example, the latest Transamerica Retirement Survey of Workers found that 40% of baby boomers expect their standard of living to fall during retirement, 83% of Generation Xers believe they'll have a harder time achieving financial security than their parents, and only 18% of millennials say they're very confident about their retirement prospects.

So how can you avoid having to ratchet down your lifestyle after calling it a career? Here are three ways:

1. Live below your means during your working years. This simple concept is something that many people have difficulty pulling off. Indeed, a 2016 Guardian Life survey on financial confidence found that nearly two-thirds of Americans say they're not good at living within their means, let alone below them. But this is critical for two reasons: By saving consistently, a portion of your earnings today will be available for future spending when the paychecks stop. And the lifestyle you will be trying to continue in retirement won't be as costly as what it might have been without the saving.

Granted, some people face such difficult financial circumstances that they have little choice but to spend all they earn. The issue for most of us, however, is finding a way to turn the resolve to save into actual dollars in a retirement account. The best way to tilt the odds in your favor is to make saving automatic, such as by enrolling in a 401(k) or other workplace retirement plan that moves money from your paycheck before you can even get your hands on it.

Generally, you want to set aside 15% or so of pay each year (including any money your employer kicks in), although you may need to step it up a bit if you're getting a late start. If you can't hit your target right away, you can work up to it gradually by boosting your savings rate a percentage point or so each year you receive a raise. If a 401(k) or similar plan isn't an option where you work, you can sign up for an automatic investing plan and have money transferred each month from your checking account into an IRA at a mutual fund company.

Putting your savings regimen on autopilot allows you to bypass the chief obstacle to saving—you, or more accurately, your natural impulse to spend. It makes it more likely that the money you intend to save actually ends up getting saved. Further, if, say, 10% to 15% of your paycheck is going into your 401(k), then you pretty much have to arrange your life so that you're able to live on the remaining 85% to 90%. In other words, you're effectively forced to live below your means.

This approach isn't foolproof. You can always sabotage yourself by running up lots of credit-card or other debt in order to overspend. But if you avoid piling on debt, save consistently and track your progress periodically—which you can do with a good retirement calculator like this free version from T. Rowe Price—you'll reduce the chance that you'll have to live a more meager lifestyle than you'd envisioned in retirement.

2. Learn to take pleasure in small things. Preparing for a secure and comfortable retirement is certainly important, but you don't want to focus on saving and controlling spending so much that you don't enjoy life. Fortunately, you don't have to live large to be happy. On the contrary. Research shows that the pleasure you receive from spending even on major expenditures and big luxuries quickly fades. So indulging in more small, less-expensive purchases may actually lead to greater happiness than splurging on high-price items.

For example, in a paper titled "If Money Doesn't Make You Happy, Then You Probably Aren't Spending It Right," researchers exploring the relationship between spending and happiness note that "if we inevitably adapt to the greatest delights that money can buy, then it may be better to indulge in a variety of frequent, small pleasures—double lattes, uptown pedicures, and high-thread-count socks—rather than pouring money into large purchases, such as sports cars, dream vacations, and front-row concert tickets."

More from RealDealRetirement.com: What Size Nest Egg Do You Need for a Secure Retirement?

Clearly, you're not going to eliminate all big-ticket expenditures during your life. But to the extent that you can find less costly yet still effective ways to treat yourself, you'll free up more money to save for retirement and be better able to manage your spending after you retire without forcing yourself to live like an ascetic.

3. Get a bigger investment bang for your savings buck. Saving regularly by living below your means is the surest way to avoid seeing your standard of living fall in retirement. But another form of saving—reducing the amount you shell out in investment costs and fees—can also help. How? Simple. Morningstar research shows that lower costs tend to boost returns, which allows you to build a larger nest egg during your career and can lower your risk of depleting your savings prematurely after you retire.

The easiest way to reap the benefits of lower investing costs is to invest your savings as much as possible in a broadly diversified portfolio of index funds or ETFs, many of which you can find with annual expenses of 0.20% or less, vs. 1% to 1.5% for many actively managed funds. Low-cost index funds and ETFs can also bestow an advantage beyond their cost savings—namely, the more you stick to a straightforward mix of stock and bond index funds, the less likely you are to fall for gimmicky or exotic investments that can make it more difficult to manage your retirement portfolio and possibly drag down long-term returns.

I can't guarantee, of course, that following these three guidelines will allow you to maintain your pre-retirement standard of living throughout your post-career life. But I can say that doing so should definitely tilt the odds in your favor.

Walter Updegrave is the editor of RealDealRetirement.com. If you have a question on retirement or investing that you would like Walter to answer online, send it to him at walter@realdealretirement.com. You can tweet Walter at @RealDealRetire.