Investing regularly into the stock market can be an effective way to build up a large portfolio by the time you retire. It's a great alternative if you don't have a large lump sum to invest today, as you can add to your position over the long term and end up with a seven-figure balance.

If you can set aside $450 per month and can put that into the stock market, I'll show you how doing that over the long term (30 years) could help you end up with a portfolio worth at least $1 million. The good news is that it doesn't involve taking much risk. By targeting top growth stocks, you can ensure that you're making the most of your investment dollars.

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An ideal fund for growth investors

One of the best exchange-traded funds (ETFs) you can invest money into on an ongoing basis is the Vanguard Growth Index Fund ETF (VUG 1.08%). As its name suggests, this fund focuses on growth stocks, and that's an excellent way to grow wealth over the long haul. Growth stocks can generate significant returns as the underlying businesses are expanding into new markets or developing new products, and finding ways to become more valuable.

There can be some greater volatility with growth stocks than with dividend stocks or value stocks. These can be safer investments, but their returns will likely be less significant over time. As long as you are looking at the long term and not just a few years, investing in growth stocks can still be the ideal way to set yourself up for massive gains.

The VUG ETF has been a terrific investment over the years, and it has outperformed the S&P 500 by a wide margin. In the chart below, you can see how much more money you'd make on a $10,000 investment in the fund versus investing in an ETF that tracks the S&P 500.

^SPX data by YCharts.

By taking the safer option and going with the broader index, you could be sacrificing a lot of gains. The Vanguard fund isn't a high-risk investment, either. While it does have heavy exposure to tech (close to 60% of its holdings are in that sector), that can enable it to produce fantastic returns for investors in the long run. And with a low expense ratio of 0.04%, it's an efficiently run ETF with minimal fees.

How your balance could grow over a period of 30 years

Regularly investing $450 per month in this ETF allows you to spread your investment over a long period, and it avoids the temptation of trying to time the market and pick the best time to invest. You're effectively averaging your position over decades. The payoff comes with building up a significant balance, which then compounds and gets even bigger. Like a snowball, once it gets big, it can get even bigger quickly. The key is getting that balance as large as possible.

If the fund were to grow at a rate of 10% per year, which is in line with the market's long-run average, here's how your portfolio balance might look, assuming you invest $450 each month into the ETF.

Table and calculations by author.

While it might take 25 years to get the balance up to over $600,000, it will take just another five years to get to over $1 million. That's where the big payoff comes from -- once that balance becomes substantial, the effect of compounding really starts to show its strength by rapidly growing your balance.

It's the effect of simple math. A 10% return on a $600,000 balance is going to be $60,000, while on a balance of $25,000, it'll only be $2,500. The larger the balance, the more meaningful the effect even average returns will have on your portfolio.

Routinely saving and investing $450 each month may not be an easy thing to do, but there's definitely an incentive to do so, as it can help put you in a strong financial position in the future.