History Says This ETF Could Turn $200 a Month Into $450,000 With Next to No Effort on Your Part. Here's How.

Building a portfolio valued at hundreds of thousands of dollars might seem like an impossible dream. But if you build it brick by brick, it's not as tough as it appears.

By investing a regular amount into a broadly diversified stock exchange-traded fund (ETF) and letting it grow for many years, you can watch a couple of hundred dollars every month turn into nearly half a million dollars or more by the time you need it.

Here's the roadmap to getting there.

Let's say you invest $200 per month into one of the broadest U.S. equity funds there is, the Vanguard Total Stock Market ETF (NYSEMKT: VTI). For many working-age folks, that's a reasonable amount to target, especially if you consider that things like 401(k) matches count toward it, too.

The long-term return for the S&P 500 has averaged about 10% annually. The Vanguard Total Stock Market ETF invests in large-, mid-, and small-cap stocks beyond the S&P 500, but that's still a fair return assumption to use.

And let's say that you've got 30 years to continue making contributions and to let the investment grow. In the end, $200 per month invested for 30 years with a 10% average annual return would turn into approximately $452,000. Small investments made consistently over time can create a nearly half-million-dollar portfolio as you approach retirement age.

More than choosing the right investments, consistency is the key to success, and time is your greatest ally. If you keep a long-term view and maintain discipline, your chances for success improve considerably.

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