Building a large share portfolio might sound like a big task, but with consistent investing and the power of compounding, it certainly is achievable.

Let's walk through how you could grow a $250,000 ASX share portfolio from scratch.

Step 1: Start with regular contributions

The first step is to make investing a habit. By committing $500 a month into ASX shares, you are putting $6,000 a year to work. This steady approach removes the need to time the market perfectly and lets you buy through both highs and lows with dollar cost averaging.

If you can automate the process through your broker, even better — that way you're never tempted to skip a month.

Step 2: Let compounding do the heavy lifting

Compounding is your best friend when investing. It helps accelerate the growth of your portfolio over time as you earn returns on both your original investments and the gains they generate. This snowball effect is the secret behind long-term wealth creation.

In the first few years, most of your growth will come from your contributions. But as the years pass, compounding will take over and your portfolio will grow faster, even without increasing your monthly investment.

Step 3: The numbers in action

So, how long will it take to reach $250,000? At $500 a month and an average 10% annual return, which is in line with historical averages (but not guaranteed), it would take just under 17 years to hit your goal.

After 10 years, you'd have invested $60,000 of your own money, but your portfolio could be worth around $100,000 thanks to compounding. By year 15, it would be over $200,000 — and in those final couple of years, the jump to $250,000 happens surprisingly quickly.

Step 4: Stay the course through market ups and downs

The key to success is consistency. Share markets will have down years — sometimes sharply — but by staying invested, reinvesting dividends, and continuing to make contributions, you allow compounding to work in your favour.

Focusing on high-quality ASX shares or diversified ETFs can help smooth your returns and reduce risk over the long term. This might include shares like ResMed Inc. (ASX: RMD) and Pro Medicus Ltd (ASX: PME), or ETFs like the Betashares Nasdaq 100 ETF (ASX: NDQ) and the iShares S&P 500 ETF (ASX: IVV).

Foolish takeaway

Starting from zero doesn't mean you can't build substantial wealth.

By investing $500 a month and earning an average 10% return, you could grow a $250,000 ASX share portfolio in under 17 years. The key is to be patient and disciplined.