Saving for retirement can be an intimidating project to undertake, especially if you don't have any savings to start with right now. But the benefit of long-term investing is that you have time on your side. You can slowly build up your position over the years, and with the help of compounding, you can still be on your way to potentially retiring with a $1 million portfolio, even with no savings today.

You'll need at least 30 years to make this strategy work without having to take on a lot of risk. But if you have that much time and you can afford to begin saving and investing right now, here's how you can put yourself on track to building up a portfolio worth at least $1 million in the future.

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Invest in a top growth fund every month

The best way to ensure that you regularly add funds to your portfolio over the long term may be to make saving and investing part of your monthly budgeting process, Nowadays, with commission fees being minimal and in some cases even close to zero, investing on a more regular basis can make a lot of sense; there's no need to wait until you've built up thousands of dollars before getting started. Plus, by making the threshold smaller, you eliminate a potential excuse for not investing.

A great place to invest is an exchange-traded fund (ETF) that's focused on long-term growth, and that has solid blue chip stocks in its portfolio.

The Invesco QQQ Trust (QQQ -0.46%) fits these criteria well. It gives you a position in the top 100 nonfinancial stocks on the Nasdaq exchange, also known as the Nasdaq-100 index. It will rebalance over time to ensure that you're always getting exposure to the best growth stocks in the world. And it can generate better returns than an index fund that tracks the S&P 500. Over the past five years, the S&P 500 has doubled in value, but the Invesco QQQ's returns are up around 120% (as of Oct. 3).

The difference in returns become even more pronounced over the previous 10-year period, with the Invesco QQQ's returns notably stronger, reaching 480% at a 19.2% annual rate, overshadowing the S&P 500's 244% return, which had an annual rate of 13.2%.

How the ETF can get you to $1 million

To reach a goal of $1 million by investing in this ETF, you'll need to make monthly investments of $300. That can seem like a significant amount, but if you're able to do it, the payoff can be large. The table below shows how a $300-per-month investment can grow after 30 or more years, assuming it rises by a rate of 10% per year, which is approximately what the S&P 500 has averaged for decades.

Year 10% Annual Growth
30 $683,798
31 $759,201
32 $842,501
33 $934,523
34 $1,036,180
35 $1,148,483

Data source: Calculations by author.

It could take around 34 years of making monthly investments of $300 before you end up with a balance of $1 million. But remember that this is based on an average annual growth rate of 10%, which is likely to fluctuate. If the long-term average returns turn out to be higher than that, which may be possible if you focus on growth stocks, then it won't take as long to get there. But on the flip side, if the market crashes or faces a prolonged downturn and the average growth rate is less than 10%, then it could very well take you longer to reach $1 million.

However, by investing in a top ETF such as the Invesco QQQ Trust, you'll still likely end up in a far stronger financial position. And that's why investing every month into that -- or other top growth ETFs -- can be a great habit to start today, even if you currently have no savings.