If there's one force in investing that deserves more attention, it is compounding.

In simple terms, compounding is when your returns start generating returns of their own. And over time, that snowballs into something pretty remarkable.

So, what happens when you combine compounding with a long-term mindset, a regular investment plan, and a healthy dose of quality ASX shares?

Let's take a look.

The ASX share plan

Let's imagine you're starting with $10,000 in savings and can invest $500 a month into the share market. You're committed to this strategy until 2040, which gives you 15 years of consistent investing.

And while nothing in the market is guaranteed, we'll assume a 10% average annual return, which is in line with historical long-term returns for the Australian share market, including dividends.

Here's what that could look like:

• Starting amount: $10,000
• Monthly investment: $500
• Time horizon: 15 years
• Annual return (assumed): 10%

By 2040, your ASX portfolio could grow to a jaw-dropping $240,000+ — built from $100,000 of total contributions and over $140,000 in growth alone. That's the magic of compounding in action.

The key? Quality

Of course, achieving strong long-term returns depends on where you invest. For those confident in picking individual stocks, companies like Goodman Group (ASX: GMG), TechnologyOne Ltd (ASX: TNE), ResMed Inc. (ASX: RMD) and CSL Ltd (ASX: CSL) have proven themselves over time with durable competitive advantages, solid earnings growth, and shareholder-friendly policies.

But if you prefer a simpler approach — or just want to sleep well at night — ASX ETFs offer a fantastic alternative.

Easy diversification with ETFs

Rather than picking stocks, you can buy entire baskets of them through exchange-traded funds. Here are a few ETFs that could help form the foundation of a quality-focused, long-term ASX portfolio.

The Vanguard Australian Shares Index ETF (ASX: VAS) gives you broad exposure to Australia's largest companies, including banks, miners, healthcare, and more. The Betashares Australian Quality ETF (ASX: AQLT) targets high-quality Aussie businesses with strong financials and consistent earnings — a great tool for compounding. And the VanEck Morningstar Wide Moat ETF (ASX: MOAT) offer access to US companies with strong competitive advantages. Perfect for adding global exposure with a quality tilt.

Foolish takeaway

It is easy to feel overwhelmed by day-to-day market noise. But long-term investing doesn't need to be complicated.

Start with what you can. Stay consistent. Focus on quality. And give compounding the time it needs to work its magic.

With a simple plan — like investing $500 a month and letting it grow — your ASX portfolio could transform your financial future by 2040. The hardest part? Getting started. But the sooner you do, the better the results could be.