Don't have a lot of money to invest in stocks? Even putting aside $50 a week can be enough to help save for retirement -- provided that you have many investing years left. You don't need to take on aggressive strategies along the way, and you can even invest in an exchange-traded fund (ETF) to help take the guesswork out of worrying if you've picked the right stocks or not.

Here's how your money could grow

If you were to save $50 per week for 30 years, you would have amassed a total of $78,000 during that time. But to make the most of that money, you'd be better off investing it. At an average growth rate of 10% per year (roughly what the S&P 500 averages), those contributions could be worth close to $500,000 -- more than six times what you saved.

It's all possible through compound interest if you let your money grow over time. Here's how those investments could rise in value:

Chart by author.

One important caveat to consider is the effect of commission costs. Nowadays there is commission-free trading; if your brokerage doesn't offer it, you may be better off pooling that $50 and investing it on a monthly basis (or perhaps quarterly) to ensure commissions aren't diminishing your returns.

Focus on profitable, growing investments

You don't need to invest all that money in one stock. You can alternate investing in different stocks each week. The key is to have some stocks that you feel comfortable holding over the long term. 

Johnson & Johnson (JNJ -0.85%) is an example of a top healthcare stock that pays a dividend yield of 2.5%. If you were to reinvest that dividend income, it could improve the odds that you get close to a 10% return each year. This is also a low-volatility stock, meaning that it won't fluctuate wildly even if the markets do. The company's business is diverse, with the bulk of its revenue coming from pharmaceuticals and medical devices.

Johnson & Johnson likely won't be doubling its sales anytime soon, but with billions in free cash flow and a growing need for healthcare (especially as seniors make up more of the U.S. population), this can be a decent, slow-growth stock to buy and hold. 

If you're targeting a more ambitious growth rate, then a stock like Intuitive Surgical (ISRG -1.90%) might make more sense. The company is in the robotic-assisted surgery market, which is still in its early growth stages. And unlike many rapidly growing businesses, Intuitive is already generating profits, so it's not nearly so risky. It's a stock that I believe has the potential to make you a millionaire and is an excellent place to invest your money for the long haul.

When in doubt, go the ETF route

If you're not sure where to invest, another option is to simply invest in an ETF. With so many available, you can invest as broadly or as narrowly as you like. The iShares U.S. Healthcare ETF (IYH -1.39%) is an excellent option to gain exposure to the healthcare sector as a whole. The fund invests in Johnson & Johnson, Intuitive Surgical, and many other top healthcare socks in the U.S.

The downside with ETFs is that their returns are often more muted than those of top-performing stocks. But on the flip side, they can minimize your overall risk. Over the past five years, Intuitive Surgical has doubled in value, while Johnson & Johnson's total return (including dividends) is more modest at 54%. By comparison, the iShares U.S. Healthcare ETF has achieved a 75% total return during that same stretch.

There is no shortage of possibilities to explore that could help you grow your portfolio's value over the years. And by focusing on fundamentals and consistently setting aside money to invest, you can put yourself in a much stronger financial position in the future.