DCA Into the S&P 500: A 20-Year Backtest That Proves the Strategy

What happens if you invest $500 every month into the S&P 500, no matter what the market does? We ran the numbers over 20 years — through crashes, rallies, and everything in between. The results speak for themselves.

What Is Dollar-Cost Averaging?

Dollar-cost averaging (DCA) is the simplest investing strategy that exists: you invest a fixed dollar amount at regular intervals, regardless of what the market is doing. When prices are high, your $500 buys fewer shares. When prices are low, it buys more. Over time, this averages out your cost per share and removes the pressure of trying to time the market perfectly.

The S&P 500 — an index of the 500 largest publicly traded US companies — has historically returned about 10% per year on average (roughly 7% after inflation). The two most popular ETFs that track it are VOO (Vanguard S&P 500 ETF, 0.03% expense ratio) and SPY (SPDR S&P 500 ETF Trust, 0.09% expense ratio). Both give you instant ownership of America's biggest companies.

The Backtest: $500/Month for 20 Years

Let's look at what happens when you invest $500 every single month into the S&P 500 for 20 years, using the index's historical average annual return of approximately 10%.

You put in $120,000 of your own money. The market did the rest. That extra ~$260,000? That's compounding doing its job. And here's the thing — the investor who earned these returns didn't need to pick stocks, read earnings reports, or watch CNBC. They just set up an automatic transfer and let it run.

Portfolio Growth Over Time

The magic of compounding is that it accelerates over time. The first few years feel slow, but by year 15 and 20, the growth curve becomes dramatic. Here's a rough breakdown of where the portfolio stands at different milestones, assuming a 10% average annual return:

Notice how the portfolio nearly doubles between years 15 and 20. That's not because you invested more — you contributed the same $500/month the entire time. It's because the compounding engine has more fuel to work with. The gains themselves start generating gains.

Buying Through the Crashes

Here's what makes DCA so powerful psychologically: it turns crashes into opportunities. A 20-year investor would have lived through some terrifying moments:

2008–2009 Financial Crisis: The S&P 500 dropped about 57% from peak to trough. Horrifying to watch. But your $500/month was buying shares at steep discounts. Those shares purchased at the bottom eventually delivered some of the best returns in the entire 20-year period.

2020 COVID Crash: The market fell roughly 34% in about five weeks. Fastest bear market in history. But the DCA investor kept buying, and the S&P 500 recovered to new all-time highs within six months.

2022 Bear Market: Rising interest rates pushed the S&P 500 down about 25%. Again, the consistent investor kept buying at lower prices, setting up the next leg of growth.

In every case, the investors who panicked and stopped contributing (or worse, sold) missed the recovery. The DCA investors who stayed the course were rewarded.

DCA vs. Lump Sum: What the Research Says

To be fair, academic research (including a well-known Vanguard study) shows that lump-sum investing — investing all your money at once — beats DCA about two-thirds of the time. This makes sense: markets go up more than they go down, so the sooner your money is invested, the more time it has to grow.

But here's the reality: most people don't have a large lump sum sitting around. They earn money through a paycheck, and they invest a portion of it regularly. That's DCA by default. And even if you do have a lump sum, many investors find DCA easier to stick with emotionally — which matters more than the theoretical optimal strategy you can't bring yourself to follow.

How to Actually Do This

Setting up a DCA strategy into the S&P 500 takes about 15 minutes:

Step 1: Open a brokerage account at Fidelity, Schwab, or Vanguard (all offer $0 commissions on ETFs).

Step 2: Buy VOO (0.03% expense ratio) or SPY (0.09% expense ratio). VOO is cheaper and equally effective for long-term investors.

Step 3: Set up automatic recurring investments. Most brokerages let you schedule weekly, biweekly, or monthly purchases.

Step 4: Don't touch it. Seriously. The hardest part of DCA isn't starting — it's resisting the urge to stop during downturns.

Want to see how different contribution amounts and time horizons would play out? Run your own scenario in our DCA Calculator.

The Bottom Line

Dollar-cost averaging $500/month into the S&P 500 over 20 years has historically turned $120,000 in contributions into roughly $380,000. That's the power of consistent investing combined with compounding. You didn't need to be smart, lucky, or well-connected. You just needed to be consistent. The strategy is boring — and that's exactly why it works.