It's fairly easy to go from having \$1 million to being broke. You might buy one fancy house or several modest ones. You might buy a fancy car, fly first class on a trip around the world, and prepay college tuition for all your kids. You might even just spend a crazy weekend in Las Vegas.

It's harder to go in the other direction, though, turning a net worth of \$0 into a net worth of \$1 million. It takes longer, too. But the important thing to understand is that it can be done. Here's how you can do it.

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## Simple math

It's really all just a matter of math. Perhaps obviously, you'll get to a million dollars by saving and investing -- fairly aggressively and very regularly. The table below shows how long it will take you to reach approximately \$1 million if you're saving and investing various sums each year. It assumes a growth rate of 8% in order to be somewhat conservative, since the average annual return of the stock market is close to 10% over many decades.

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

So if you're socking away \$10,000 annually, you can get there in about 28 years, and it will take only about 20.5 years if you can regularly save and invest \$20,000.

So how are you going to aim for that average annual growth rate of 8%? The best way, arguably, is to just invest in a good low-fee index fund, or a few of them. Here are a few index-based exchange-traded funds (ETFs) that can serve you well:

• The SPDR S&P 500 ETF : This ETF tracks the S&P 500 index of 500 of America's biggest companies. The S&P 500 is often used as a proxy for the overall U.S. market, as its holdings make up about 80% of the total value of the U.S. stock market.
• The Vanguard Total Stock Market ETF : This ETF encompasses all of the U.S. stock market, including the many smaller companies not in the S&P 500.
• The Vanguard Total World Stock ETF : This ETF tracks the whole world's stock markets, including the U.S. market.

Over relatively short periods, such as 10 or even 20 years, the S&P 500 or broader markets might not average as much as 8%, and they might average more. There's no way to know. So try to hope for the best but plan for the worst.

It can help to be aggressive in your saving. If you're able to sock away \$10,000 per year, see if you can do \$12,000 instead. The earliest dollars you invest will have the longest time in which to grow for you, so it's not crazy to consider taking on a side hustle for a while, to earn extra early dollars. If you're carrying high-interest-rate debt, be sure to pay that off before investing, because you won't get ahead trying to earn 8% or 10% in the stock market while paying 20% or 25% annual interest on debt.

Once you have a good plan in place, stick with it. The most important factor in your success will be your determination.

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.