The stock market can be daunting at times, especially during periods of volatility. But investing remains one of the simplest and most effective ways to build wealth over time, and it's possible to earn hundreds of thousands of dollars or more.

However, you'll need the right strategy to pull off that achievement. Fortunately, with just one low-maintenance investment, it's possible to turn $100 per week into $790,000 while barely lifting a finger. Here's how.

Generating wealth with next to no effort

There are countless investments to choose from, and where you buy will depend on your personal preferences and risk tolerance. But if you're looking for a low-effort investment to put your savings on auto-pilot, the S&P 500 ETF may be a smart choice.

The S&P 500 ETF -- such as the Vanguard S&P 500 ETF (VOO 0.28%) tracks the S&P 500 index itself. This means it includes the same stocks as the index or roughly 500 stocks from the largest and strongest companies in the U.S.

In other words, when you invest in just one ETF, you'll instantly own a stake in all 500 of these companies -- ranging from tech behemoths like Amazon and Apple to household names like Procter & Gamble and Coca-Cola.

This level of diversification can significantly lower your risk because you'll own a wide variety of stocks across multiple industries. And because the companies within the S&P 500 are some of the strongest in the world, this investment is extremely likely to recover from market downturns and go on to see consistent long-term growth.

Building a $790,000 portfolio

Perhaps the biggest advantage of the S&P 500 ETF is that it's a low-maintenance investment. You never need to worry about choosing stocks, deciding when to buy or sell, or keeping up with industry news. Simply invest whatever you can afford, then wait for your money to grow.

Historically, the S&P 500 itself has earned an average annual return of around 10% per year. While it's highly unlikely you'll earn 10% returns each and every year, the annual highs and lows should average out to around 10% per year over several decades.

Assuming your investment is earning a 10% average annual return, here's approximately how much you could accumulate over time by investing just $100 per week:

Number of Years Total Savings
20 $275,000
25 $472,000
30 $790,000
35 $1,301,000
40 $2,124,000

Data source: Author's calculations via Investor.gov

To build a portfolio worth $790,000, you'd need to invest consistently for around 30 years. But if you have even a few more years to invest, you could earn exponentially more. Time is your most valuable resource, so the sooner you get started investing, the easier it will be to make a lot of money.

One drawback to consider before you buy

The S&P 500 ETF is a fantastic choice for those looking for a low-cost investment that requires very little upkeep. However, it won't be the right fit for every portfolio.

If you're looking to earn above-average returns, for example, the S&P 500 ETF won't get you there. Because this investment is designed to follow the market, it's impossible for it to beat the market.

For many people, lower returns are a worthwhile trade-off for the ease and simplicity of this investment. But if you're aiming to truly maximize your earnings in the stock market, you may be better off investing in individual stocks. While they do require more effort than this ETF, you could potentially earn far higher returns.

Generating wealth in the stock market doesn't have to be complicated, but you will need the right investments. If you're looking for a "set it and forget it" type of investment that can help you make money while barely lifting a finger, the S&P 500 ETF may be a great fit for you.