Many investors dream of building a million-dollar portfolio, but few realise that it doesn't take a massive upfront investment to achieve this goal.

With a combination of patience, consistency, and a smart approach to investing in quality ASX shares, you could potentially grow your portfolio to $1 million over time—even if you start with just $5,000.

The power of compounding

One of the most powerful forces in investing is compounding. This is when your returns generate additional returns over time, supercharging portfolio growth.

Historically, the share market has delivered an average total return of around 10% per annum. And while this is not guaranteed again in the future, I feel it is a fair return to base our assumptions on.

With that in mind, if you were to start with a $5,000 investment and contribute an additional $500 per month into high-quality ASX shares, your portfolio could grow to over $1 million within 30 years, assuming that average annual return.

Investing in quality ASX shares

To maximise your chances of reaching this milestone, it is important to invest in the highest quality ASX shares you can find. These usually boast qualities such as strong and sustainable business models, talented management teams, and positive long-term growth outlooks. Here's what to look for:

• Strong fundamentals: Companies with solid revenue growth, strong profit margins, and healthy balance sheets tend to deliver consistent returns over time.
• Competitive advantages: Businesses with economic moats—such as brand strength, intellectual property, or cost advantages—are more likely to sustain profitability.
• Resilient industries: Investing in sectors that benefit from long-term tailwinds, such as technology, healthcare, and consumer staples, can improve your portfolio's stability and growth potential.

Companies such as ResMed Inc. (ASX: RMD) and Accent Group Ltd (ASX: AX1) could tick these boxes.

The importance of consistency

One of the key factors in building a successful ASX share portfolio is maintaining consistency.

Market fluctuations are inevitable, but investors who stick to a disciplined investment plan, regularly adding to their portfolio regardless of short-term volatility, are often rewarded in the long run.

Dollar-cost averaging—investing a fixed amount each month—helps reduce the impact of market ups and downs, allowing you to accumulate shares at different price points.

Patience is key

Reaching $1 million won't happen overnight. However, those who remain patient and committed to their investment strategy are more likely to see substantial long-term results.

Selling out during market downturns or chasing short-term gains from highly speculative stocks such as meme stock Brainchip Ltd (ASX: BRN) can hinder your ability to fully benefit from compounding returns. Instead, focusing on long-term growth and reinvesting dividends can significantly accelerate portfolio growth.

Foolish takeaway

By starting with just $5,000 and consistently investing $500 each month into high-quality ASX shares, you could potentially build a million-dollar portfolio within three decades.

While market returns are never guaranteed, history suggests that a disciplined and patient approach to investing in great companies gives you the best chance of achieving financial success.