Most of us would like to become millionaires, but it can seem impossible unless you are a stock market genius or lucky casino frequenter. That's not the case, though. As long as you have enough time before you retire, it's possible to amass surprisingly large sums -- even a million dollars or more.

Better still, this can be done very simply, such as by only investing in a broad market index fund. Since many exchange-traded funds (ETFs) exist that track many different stock market indexes, you can achieve millionairehood via ETFs.

A happy couple embracing and smiling.

Image source: Getty Images.

How money grows

The proof of how much money you can amass over time is in the math -- reflected in the table below. Much depends on how long you invest and on how much money you invest regularly. The bolded numbers below show the points at which you might cross the millionaire line when you're saving various sums for various periods.

Growing at 8% for

$10,000 invested annually

$15,000 invested annually

$20,000 invested annually

5 years

$63,359

$95,039

$126,718

10 years

$156,455

$234,683

$312,910

15 years

$293,243

$439,865

$586,486

20 years

$494,229

$741,344

$988,458

20.5 years

$518,914

$778,371

$1,037,828

23.5 years

$688,744

$1,033,115

$1,377,487

25 years

$789,544

$1,184,316

$1,579,088

28 years

$1,029,659

$1,544,489

$2,059,319

30 years

$1,223,459

$1,835,189

$2,446,918

Data source: Calculations by author.

The table uses an 8% annual growth rate, and that's an attempt to be somewhat conservative. Over long periods, the average stock market return has been roughly 10%, but an investor might average a little or a lot more or less depending on the specific period in which they invest.

A road sign says Millionaire Next Exit.

Image source: Getty Images.

Some ETFs to consider

So which specific ETFs can help you amass significant wealth? Well, there are lots of great low-cost ETFs that are passively managed index funds, and fund companies such as Vanguard, Fidelity Investments, and Schwab. Here are a handful of solid contenders that encompass much or all of the U.S. or world stock market:

The following ETFs focus on companies of certain sizes:

Finally, here are some ETFs that have particularly strong performances over the past 10 and 15 years. That's not necessarily guaranteed to continue, so be sure to read up on any of them before investing in them, to make sure you like what you see and that you're confident in their promise.

  • Invesco QQQ Trust (NASDAQ:QQQ): This ETF tracks the Nasdaq-100 Index of the 100 largest non-financial companies that trade on the Nasdaq market.
  • Vanguard Information Technology ETF (NYSEMKT:VGT): This ETF is heavily invested in technology stocks such as Apple, Microsoft, and NVIDIA.
  • SPDR S&P Biotech ETF (NYSEMKT:XBI): This ETF is focused, obviously, on the biotech arena, with holdings such as Moderna and Curis.

If you end up invested in one or more ETFs that grow significantly faster than the overall market, you may become a millionaire even faster than if you just stick with an S&P 500 or world market ETF. But even those very broad ETFs have very respectable records and are likely to be solid performers over the coming decades.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.