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I probably don't need to tell you this, but saving for retirement isn't easy.

There are a seemingly countless number of obstacles that stand in the way of our ideal retirement plans. These include unexpected medical expenses, starting a family, going to college or paying for your children's education, and being laid off. Any number of changes can send your saving and investing plans for a loop, causing you to rework how much you save and invest, and potentially delaying your retirement.

But saving and investing are only the half of it. Workers and retirees also need to ensure that their nest egg and income stream are outpacing the national rate of inflation. For example, if your money is earning only 1% a year, but the inflation rate is 2% a year, you're actually losing real money. In this instance, you'd be gaining nominal value on your principal, but you'd be losing purchasing power as your investments aren't keeping pace with the rising costs of goods and services. 

Two surprising ways your purchasing power is being eroded

Staying ahead of inflation isn't always easy. In fact, two commonly relied-upon income streams could be eroding the purchasing power of Americans without them realizing it.

Social Security

For seniors, there's arguably no source of income more important than Social Security. A Gallup poll from 2015 found that nearly 6 in 10 seniors count on Social Security to provide a majority of their retirement income, with another 3 in 10 relying on Social Security as a minor source of income. But when it comes to meeting the financial needs of seniors, Social Security appears to be failing.

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Social Security benefits are adjusted annually using the Consumer Price Index for Urban Wage Earners and Clerical Workers, or CPI-W. The average CPI-W from the third quarter of the previous year serves as the baseline number, while the average CPI-W in the third quarter of the current year serves as the basis for determining whether or not beneficiaries will get a "raise." If the CPI-W increases, Social Security beneficiaries receive an increase commensurate with the percentage difference. If it decreases, benefits stay flat year over year.

Three times over the last seven years Social Security beneficiaries haven't received a cost-of-living adjustment, or COLA. All the while, the price seniors are paying for medical care and housing continues to climb. Specifically, healthcare inflation has outpaced the normal rate of inflation (measured by the consumer price index) in all but one year between 2005 and 2015. Although COLA is keeping pace with the cost for everyday goods like food and entertainment, increases in housing and healthcare costs could continue to pinch seniors and reduce their purchasing power during their golden years.

U.S. Treasury bonds

Another "say it ain't so" moment can be found with consumers currently buying U.S. Treasury bonds (or bank CDs for that matter).

For decades, U.S. T-bonds have been counted on, along with bank CDs and other forms of low-risk investments, to provide near-guaranteed interest-based income. It's likely your parents, and their parents, have at some point counted on the interest-earning power of T-bonds to outpace inflation. For many years this worked. Unfortunately, that train appears to have left the station.

Image source: U.S. Department of the Treasury.

As you can see in the above snip published by the U.S. Department of the Treasury, the daily Treasury yields have been on a precipitous decline for years. Currently, A one-year bond would yield just 0.45%, a five-year only 1%, and a 30-year just 2.24%. Mind you, the historic rate of inflation between 1914 and 2014 was well over 3%, meaning if you were to purchase a T-bond at today's yields, you'd almost certainly lose real money and thus purchasing power over the long run. The only exception where you could see success is if the U.S. economy entered a pretty long period of weak growth or recession that resulted in stagnant, but low, inflation or even deflation.

The T-bond, a longtime mainstay income stream, has now turned into a deceptive destroyer of purchasing power for working Americans and senior citizens.

This tried-and-true investment beats inflation over the long term

Although it can be volatile at times, the stock market remains the tried-and-true investment vehicle that gives investors the best chance of outpacing inflation over the long term.

Historically, the stock market has returned an average of 7% per year, including dividend reinvestment. This would suggest that stocks have, on average, doubled the historic rate of inflation over the past 100 years and allowed investors the opportunity to build real wealth.

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But just as important to investing in the stock market is the idea that your investments should be geared for the long term. Trying to time your investments in order to avoid a market swoon simply isn't wise, because you could miss a major move higher in stocks.

A study from J.P. Morgan Asset Management, using data from Lipper, found that if you'd invested $10,000 in the S&P 500 on Jan. 3, 1995 and stayed invested through Dec. 31, 2014, you'd have earned 9.9% per year for a total return of 555%. If, however, you missed just 30 of the best trading days, your return per year fell to just 1.5%, or 34% overall. The study specifically points out that six of the market's best days over this 20-year period came within two weeks of its 10 worst trading days. Simply selling out of the market because it's turbulent isn't a smart move.

If you're looking for a way to get your purchasing power back, consider putting your money to work in the stock market.