1 Low-Cost Vanguard ETF Could Turn $300 per Month Into a $1 Million Portfolio. Here's How.

It's a dream for most people to earn the title of "millionaire." There's a perception that in order to reach the $1 million mark, you need to either win the lottery or be the beneficiary of a major inheritance.

In reality, building an investment portfolio to $1 million is far more attainable than you might think. I won't tell you that it's easy, though. It requires years of steady contributions, discipline, and investing your money in the right thing.

But if you have a plan, you can reach this target. If you have just a few hundred dollars per month to commit to this goal, it's time to get started.

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The path to $1 million by investing just $300 per month

When getting started, a financial calculator can be invaluable. I like this one. Plug in a few numbers, and you'll find out quickly exactly what it takes to get there.

For long-term investing goals, I like the Vanguard Total Stock Market ETF (NYSEMKT: VTI). Instead of focusing only on large-cap stocks, it invests in the entire investable U.S. stock universe, more than 3,000 stocks in all. Using a diversified equity fund like this one captures the potential of the full U.S. economy without exposing yourself to undue risk from any single company. And you don't need to worry about picking winners!

Over the past century, the U.S. stock market has returned roughly 10% per year. While there's no guarantee that this is what stocks will return in the future, it's a reasonable assumption.

With these numbers in place, we can use our financial calculator. If you assume that the Vanguard Total Stock Market ETF can return 10% annually, you start with a balance of zero, and invest $300 per month, it will take just short of 34 years to reach the $1 million mark.

That kind of time frame, of course, means the earlier you start, the better. But even if you don't start early, you can still get there (or at least make strong progress). The biggest lever to pull is how much you contribute. Increasing the monthly contribution from $300 to $500, for example, shortens the timeline to 29 years. The more you contribute, the faster you get there.

The monthly contribution amount may not be that daunting either. If you have a $60,000 salary and contribute 10% of your paycheck to a workplace retirement plan like a 401(k), that's a $500 monthly contribution right there. Plus, it's tax-advantaged, and you might get a company match on top of it to grow your savings even faster.

The idea of making yourself a millionaire may seem daunting on its own. Break it down to numbers and what you need to do to get there, though, and you'll find the goal is much more achievable than you think.

David Dierking has positions in Vanguard Total Stock Market ETF. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.