Starting from zero can feel like the hardest part of investing.
There is no portfolio yet. No momentum. Just a decision to begin.
But I actually think this is one of the best positions to be in. You have complete flexibility. No legacy holdings, no need to unwind past decisions. Just a clean slate and a long runway ahead.
If I were starting today with the goal of building a $100,000 ASX shares portfolio, this is how I would approach it.

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Step one: focus on consistency
The first thing I would accept is that I do not need a large lump sum to get started. Instead, I would focus on investing in ASX shares regularly.
Whether it is $500 a month, $1,000 a quarter, or whatever is realistic for my budget, I think consistency matters far more than trying to wait until I have a big amount to invest.
In my experience, the habit of investing is more important than the initial amount. Once that habit is in place, the portfolio can begin to grow steadily over time.
Step two: start with a strong foundation
If I am building from scratch, I want a solid base early on.
For me, that would likely mean starting with a broad market exchange-traded fund (ETF) like the Vanguard Australian Shares Index ETF (ASX: VAS).
It gives instant diversification across the Australian share market, including large caps, mid caps, and smaller companies. That reduces the risk of being too reliant on any one stock in the early stages.
I would keep adding to this core position as I build the portfolio, particularly in the beginning.
Step three: gradually introduce high-quality ASX shares
Once the portfolio starts to take shape, I would begin adding individual ASX shares.
This is where I would focus on quality over quantity.
I would rather own a small number of strong businesses than spread myself too thin across too many names. Companies like CSL Ltd (ASX: CSL), ResMed Inc. (ASX: RMD), and Goodman Group (ASX: GMG) stand out to me as examples of businesses with long-term growth potential.
I would not rush this step.
Instead, I would build positions gradually over time, adding ASX shares when I have new funds available rather than trying to time the market perfectly.
Step four: think about allocation
As the portfolio grows, I would start thinking more deliberately about allocation.
For example, I might aim for a mix that includes a core ETF holding, a handful of growth-oriented companies, and perhaps some more defensive or income-focused names.
That could include businesses like Commonwealth Bank of Australia (ASX: CBA), which I think can provide a level of stability and income alongside higher-growth holdings.
The exact balance would evolve over time, but the key for me would be avoiding overexposure to any single company or sector.
Step five: stay patient
Reaching $100,000 with ASX shares will not happen overnight. It will likely take years of consistent investing, market ups and downs, and staying committed to the plan.
I think the biggest risk along the way is not market volatility. It is losing discipline.
Changing strategy too often, chasing trends or speculative stocks, or trying to outguess the market can all slow progress.
Personally, I would aim to keep things simple. Invest regularly, focus on quality ASX shares, and give the portfolio time to grow.
Foolish takeaway
Building a $100,000 ASX shares portfolio from zero is less about finding the perfect stock and more about building the right habits.
For me, that means starting with a diversified foundation, adding high-quality businesses over time, and staying consistent through market cycles.
It might feel slow at the beginning. But with patience and discipline, I believe it is achievable in time.