History Says This 1 Simple Strategy Could Build Life-Changing Wealth, and It Requires Next to No Effort

Making big money in the stock market might be less work than you think. It doesn't require picking hot stocks, obsessively following the latest financial news, or making rapid-fire day trades. (In fact, day trading is more likely to hurt you.)

Some of the best stock-market wealth-creation accrues to people who "do" the least. People who use a simple strategy. People who stay calm and consistently put more money into their stock investments, month after month, year after year -- and then get out of the way and let that money grow for years to come. That's not an easy thing to do, but it can really pay off.

Let's look at one simple strategy to build life-changing wealth with stock market investments, and how the math might look for you.

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S&P 500 average annual returns: 10% for 98 years

You don't have to buy individual stocks to get rich from investing in the stock market. Buying shares of a fund that tracks the S&P 500 index (SNPINDEX: ^GSPC), which is one of the most-watched groups of stocks in America, might be enough. This index consists of the stocks of the 500 largest publicly traded companies in America. When the American economy grows -- when companies are making good money and growing, when people are spending at malls and restaurants and online retailers -- the S&P 500 tends to do well.

Even when times are bad, the S&P 500 tends to recover relatively quickly, and it makes up for short-term downturns with long-term gains. In the 98 years since 1928, the S&P 500 has delivered average annual returns of roughly 10%. That includes years when it rose and years when it fell hard. That return is not guaranteed in any year, but it's a reasonable baseline expectation over many years.

Stocks tend to go up in the long run and be the best choice for many people to put their money into for long-term wealth-building.

How this ETF can grow your wealth along with the S&P 500

In the past 10 years, the S&P 500 has done even better than that (already impressive) long-term average. The Vanguard S&P 500 ETF (NYSEMKT: VOO) is a popular exchange-traded fund that lets investors own all the stocks of the S&P 500 index. Just buying VOO and leaving that money alone to grow -- which some folks call "VOO and chill" -- can be a great investment strategy.

In the past 10 years, VOO has delivered 15.3% average annual returns.

Future returns are not guaranteed, but here's some fun math: If you invested $1,000 and it kept growing at that same 15.3% rate, after one year you'd have $1,153. After two years, you'd have $1,329. After three years, you'd have $1,533. This is how money compounds. After five years, your money would have doubled (and then some), reaching $2,038.

How long could it take to make life-changing wealth with the S&P 500

What does life-changing wealth mean to you? Is it $500,000? How long would it take to get to that level just by investing in the S&P 500 with VOO?

Keep in mind that future returns are not guaranteed. Just because the S&P 500 has delivered roughly 10% annualized returns for the past 98 years doesn't mean it will keep doing that forever. The stock market could struggle for years; the economy could change in ways that are bad for stocks. But let's assume your S&P 500 investment would earn 10% annualized returns.

If you invest $300 per month in VOO and the S&P 500 delivers 10% average annual returns for the next few decades. After five years, you'd have $36,616. After 10 years, you'd have $95,533. After 20 years, you'd have $342,870. And after 24 years, you'd have $529,469.

Lots of bad news can happen every day in the stock market. Crises, crashes, and bear markets happen. But in the long run, patient, consistent, buy-and-hold investors tend to win. It's a simple strategy, but it works. Hopefully it will keep working for decades to come.

Ben Gran has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Vanguard S&P 500 ETF. The Motley Fool has a disclosure policy.