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What's the best way to save money for the long term? Deposit it into a simple savings account? Put it into gold? Invest in stocks? Buy supposedly safe and reliable Treasury bonds?

We'll show you the answer, but first, think of your favorite uncle. (Don't have a favorite uncle? Then, just play along!)

Let's say that on the day you were born, he wanted to invest $2,000 in your future. And, he considered stocks, gold, bonds or a savings account. Depending on his choice, how much would you have today? Use our cool tool below and see.

Which would have been the best gift at your birth?

Select your birth year and see how a $2,000 gift would have grown, depending on how it was invested

The winner?

What you find is that for most birth years, the best investment your dear uncle could have made for you would have been in the stock market.

"If you have 10-plus years to invest, stocks should be the place to put your money, especially if you have 15 or more years," concludes Tenpao Lee, professor of economics at Niagara University in New York.

Adds Mike Allen, a portfolio manager with the automated investment service Wealthsimple: "The data is very clear that the smartest way to invest for the long-term is in a broadly diversified, low-fee portfolio."

Let's take a closer look at the four different investing scenarios.

1. Stocks

Stock market chart,Stock market data on LED display concept.
Jirapong Manustrong / Shutterstock
It's hard to beat a very basic investment in an index fund that tracks the stock market.

To the uninitiated, stocks can seem scary and volatile. But the key is spreading your risk over many stocks, such as through an index fund that mimics the S&P 500 index, which represents the stocks of 500 major companies.

"Index funds are a great way to keep fees low while diversifying investments," says Allen, of Wealthsimple.

"Even Warren Buffett is a firm believer in S&P 500 index funds," Allen says. "They're low-cost, and instead of trying to guess that one winning stock — and most investors guess wrong — you're buying into all the big companies."

Our tool's results for stocks are based on the performance of the S&P 500.

For most birth years, a $2,000 investment would have yielded average returns of 7% a year or better — up to 12% if you were born during a recession, when stocks were down.

2. Gold

Stacking gold coins with increase on the beautiful bokeh and gold bar background, Saving money and loan for prepare in the future.
Watchara Ritjan / Shutterstock
Gold can be a volatile and unreliable investment.

While our tool shows a few years that are exceptions — with gold coming out ahead of stocks — Niagara University's Lee calls gold unattractive and risky, particularly in recent years.

"Most gold returns happened in a high inflationary era, such as the 1970s and 1980s," he says.

Investing in precious metals offers just a slim chance of a high return over a period of decades.

"To thrive with gold you must time — both in and out — near perfectly, or be content with long periods of losing results,” writes billionaire investor Ken Fisher in his 2011 book Debunkery.

Gold had a few booms since 1970. But it rarely beats the S&P 500 as a long-term investment.

3. Bonds

U.S. Department of Treasury with statue of Alexander Hamilton, Washington DC
Joseph Sohm / Shutterstock
U.S. Treasury bonds are known as a safe investment. Too safe.

When the U.S. government wants to raise more money, it sells Treasury bonds, which pay interest.

It sure sounds safe: The most powerful country on Earth guarantees you a return on your investment if you let Uncle Sam borrow your money for anywhere from a few weeks to a few decades.

But the data — and our tool — show that bonds just can't beat stocks over the long run.

In 1981, Treasury bond yields hit their all-time high levels, above 15%. A $2,000 investment in bonds that year would have been worth more than $12,000 by 2011, we calculate.

But that same amount of money invested in an S&P index fund in 1981 would have given you more than $20,000 after 30 years.

4. Savings accounts

Business man hands holding saving account passbook with calculator, account and saving concept.
Worawee Meepian / Shutterstock
The interest on savings accounts can be really puny.

Savings accounts are arguably the safest place to store cash while earning interest. After all, the federal government insures up to $250,000 in deposits.

But the interest can be puny, and rising prices can even make your savings worth less.

While there is no freely available data showing average interest rates for basic savings accounts, the Federal Reserve tracks rates for 6-month certificates of deposit, which are a little higher than savings rates.

Those rates have been stuck well below 1%, on an annual basis, for years.

Meanwhile, annual inflation rates over the last 10 years have been as high as 3.8%. If you park your savings in a bank account for years and earn interest, your money won't have the same buying power when you withdraw it as it does today.

Let's hope that sweet uncle of yours would have realized that.

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