With the market down substantially from its all-time highs, the benefits of dollar-cost averaging into a low-cost, broad-based stock index fund are becoming quite clear. By making regular investments every payday in this market, each dollar you're investing buys that many more shares while stocks are down. That may not seem like much benefit now, but it means you've got that many more shares available to compound in any recovery that follows.

It's with that backdrop that making regular investments in the SPDR S&P 500 ETF Trust (SPY -0.13%) starting now could make you a millionaire retiree. It's a process that takes time no matter what the market is doing, which is a great reason to consider starting those investments now, even if the market continues to fall.

Investor looking at a screen of ETFs

Image source: Getty Images

Why invest in the SPDR S&P 500 ETF Trust?

The SPDR S&P 500 ETF Trust is a low-cost index ETF that attempts to track the S&P 500 index, which is often used as a proxy for the overall US stock market. With itd expense ratio of 0.09%, investors in that ETF can get returns that nearly perfectly match that index, while losing almost nothing to fund management fees.

That combination of stock market like returns with very low internal costs makes the SPDR S&P 500 ETF trust a simple, one-stop shop for investors. It's especially potent for investors who don't want or are otherwise unable to put a lot of time and effort into digging through financial reports to pick individual stocks. When you add the fact that index investing tends to beat funds managed by Wall Street's best and brightest over time, the SPDR S&P 500 ETF Trust become an even more compelling option.

How long will it take to become a millionaire?

The path from $0 to $1 million depends heavily on two key factors: how much you're able to invest every month and what rate of return you earn along the way. The good news is that if you've got a long enough time horizon, reaching millionaire status by retirement age is feasible, even for people with modest incomes.

The following table shows how many years it takes to reach that millionaire status, depending on what you can save each month and what annual rate of return you earn along the way.

Monthly Investment

10% Annual Returns

8% Annual Returns

6% Annual Returns

4% Annual Returns































Data source: author.

The top end of that savings rate -- $2,200 per month -- represents a savings rate that can be contributed to tax-advantaged, retirement-focused accounts for most people. Workers under age 50 can generally contribute up to $20,500 per year in a company-sponsored retirement plan like a 401(k). They can also typically sock away up to $6,000 per year in their own IRA.  (The contribution limits are even higher for workers ages 50 and up. )

The bottom end of that savings rate -- $300 per month -- works out to around $10 per day. Even at that savings level, as long as you invest consistently throughout the length of a typical working career, you've got a decent shot at reaching millionaire status by the time you retire.

Get started now

Regardless of where you are in your career, you'll never again have more time before you retire than you do right now. That makes today a great day to get your plan in place. The sooner you get started, the more of the cells in that table will be within your reach, improving your chances of retiring a millionaire.