You can become a millionaire with just four investments. That may sound too easy, but it's true.

And you don't even need to think too hard about the investments you choose. Four Vanguard exchange-traded funds (ETFs) are enough. Here's what they are and how they can form the basis of a millionaire-making long-term investment plan.

Getting down to business

You can build a powerful, global portfolio with these four Vanguard ETFs: Vanguard Total Stock Market ETF (VTI 0.93%), Vanguard Total International Stock ETF (VXUS 0.81%), Vanguard Total Bond Market ETF (BND 0.23%), and Vanguard Total International Bond ETF (BNDX 0.27%). That's really all you need.

Three golden eggs in a basket made of money.

Image source: Getty Images.

The next step is to decide on how much of your portfolio should go into each of these exchange-traded funds. While that can be a nuanced discussion and personal to each individual, there are some broad guidelines that make sense for most investors. For example, 60% in equity investments and 40% in bonds is a tried-and-true portfolio mix. As for domestic versus foreign exposure, most investors will probably be more comfortable focusing domestically with, say, 75% of their portfolio.

At the end of the day, that leaves the mix something like this:

  • 45% of assets in Vanguard Total Stock Market
  • 15% in Vanguard Total International Stock
  • 30% in Vanguard Total Bond Market
  • 10% in Vanguard Total International Bond

You can, of course, adjust those percentages to ones that fit better with your investment needs and risk tolerance. Note that more equity exposure will likely lead to more growth, but it will increase risk.

Once you get that set up, you just have two more steps to worry about for the rest of your investment life.

Step one is to rebalance the portfolio roughly once a year. That will require selling some ETFs and buying others so that the portfolio mix comes back in line with the targets you are comfortable with. There's no need to be exact; close is good enough.

Step two is the bigger one and something that has to happen far more regularly: save, save, and save some more. Basically, you need to work hard to live below your means so you can put as much money as possible into your investments. That, in the end, will have the biggest impact on your long-term wealth. You can invest that cash as you save it, if you like, but simply leaving it in cash until you rebalance annually would be easier and, over the long term, a perfectly fine choice.

But that's it. That's the entire investment plan. It's a simple but effective way to build a million-dollar nest egg. It won't happen overnight, and you'll have to stick to the plan through both good times and bad (in the stock market and in your life). But if history is any guide, this easy-to-build and maintain four-ETF portfolio should get you to seven digits if you stick with it long enough.

Why these four Vanguard ETFs?

The reason these four Vanguard ETFs are almost perfect options for this portfolio is basically contained in their names, noting that each has the word "total" in it.

With Vanguard Total Stock Market ETF, you are getting exposure to the entire U.S. stock market. With Vanguard Total International Stock ETF, you are getting exposure to virtually all the important equity markets throughout the rest of the world. The same logic holds with Vanguard Total Bond Market and Vanguard Total International Bond, just for fixed-income investments.

Four ETFs and you pretty much own the world. As the world grows, your portfolio should grow with it.

As an added bonus, these Vanguard ETFs have extremely low expense ratios. Vanguard Total Stock Market ETF and Vanguard Total Bond Market ETF both charge just 0.03%. Vanguard Total International Stock's expense ratio is 0.08%, and Vanguard Total International Bond is 0.07%. These two ETFs are more expensive to own because of the added work of investing across multiple foreign markets, but the costs are still ultra low on an absolute basis.

The one drawback is that you may have to pay commissions on the trades you make with these ETFs. However, many brokers now allow for free trading of ETFs. And even if yours doesn't, each year you will make a maximum of four trades with annual rebalancing (setting up the portfolio will, similarly, require just four trades).

So the actual trading costs will be low even if you pay commissions. Four trades a year, meanwhile, won't require a huge amount of time or effort, either.

Slow and steady wins the race

You won't likely brag about this four-Vanguard ETF portfolio at your next dinner party. And over the short term, it will be about as exciting for you as watching paint dry. But over the long term, if you continue to focus on saving and rebalance the portfolio once a year, it should serve you well and help you get to millionaire status. Investing doesn't have to be hard, but it does require a lifelong commitment.