When it comes to stock market performance, investors often watch for those eye‐popping 20%+ annual gains in the S&P 500. While a single 20% year isn’t terribly rare, consecutive such years are a different story. Let’s explore how many times this has happened, the aftermath in each case, and what (little) history can tell us about the odds for the next year going 20% or more.

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1. A Century of Data: The Seven “Streaks”

We have roughly 100 years of price‐index data on the S&P 500 (or its predecessor indices, going back to the mid‐1920s). During that span, only seven runs of consecutive 20%+ annual returns have occurred:

1. 1924–1925
2. 1927–1928
3. 1935–1936
4. 1942–1943
5. 1954–1955
6. 1995–1996–1997–1998 (four straight years!)
7. 2023–2024 (the current streak)

As you can see, it’s pretty unusual—about once a decade or so on average. Sometimes many decades go by without a multi‐year 20% streak (e.g., from 1955 to 1995 was a 40‐year gap!).

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2. What Happened the Year After?

a) Historical Break Years

For the first six streaks (where we know how they ended), here’s the year that broke each streak (i.e., came in below +20%) and its approximate S&P 500 price return:

Streak	Break Year	Return
1924–1925	1926	+12%
1927–1928	1929	−11%
1935–1936	1937	−35%
1942–1943	1944	+19%
1954–1955	1956	+2.5%
1995–1996–1997–1998	1999	+19.5%

Only 1999 even came close to another 20% year (it was around +19.5%), but it still fell short—ending that rare four‐year streak from the 1990s tech‐boom era.

b) Odds of a 3rd (or 4th) Straight 20% Year

Looking at two‐year streaks (the first five of the table above):

• 1924–25 → 1926 was +12%
• 1927–28 → 1929 was –11%
• 1935–36 → 1937 was –35%
• 1942–43 → 1944 was +19%
• 1954–55 → 1956 was +2.5%

None of these went on to notch a third consecutive year above +20%.

By contrast, 1995–1996 did evolve into a 4‐year 20%+ run (1995–1998). That’s really the only modern example where two years of 20% led to more years of 20%. So historically, we’ve had:

• 6 total “two‐year streaks” that have fully played out (excluding the ongoing 2023–2024).
• 1 of those 6 extended into a three‐year (and ultimately four‐year) streak.
• That’s roughly a 17% chance (1 out of 6) that a two‐year 20% streak continues into a third 20% year.

Yes, we’re dealing with a very small sample—and times have changed drastically from the 1920s and 1930s—so treat these “odds” with a grain of salt.

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3. Probabilities for 2025: Another 20%? Another 10%?

With the new 2023–2024 streak, the natural question is: Could 2025 also be 20%+? Or at least 10%+?

a) 20%+ Probability

Using our tiny sample of two‐year streaks:

• Historically, we’ve had 6 completed two‐year streaks (1924–25, 1927–28, 1935–36, 1942–43, 1954–55, and 1995–96 which continued through 1997–98).
• Only once (the mid‐’90s) did the streak extend beyond two years.

So, from a purely “numbers in a vacuum” perspective, that’s a 1/6 = ~17% chance.

b) 10%+ Probability

Rather than focusing on 20%, some may wonder: “Is 2025 at least likely to be decent, say +10%?” We can take a narrower look at how the next year performed after each two‐year 20% streak:

1. 1926: +12% (post‐1924–25)
2. 1929: −11% (post‐1927–28)
3. 1937: −35% (post‐1935–36)
4. 1944: +19% (post‐1942–43)
5. 1956: +2.5% (post‐1954–55)
6. 1999: +19.5% (post‐1995–98, which was actually a four‐year streak, but let’s include it)

Out of these 6 “post‐streak” years:

• 3 had returns of +10% or more (1926, 1944, 1999).
• 3 had returns below +10%—two of them actually had negative returns (1929, 1937), and one was mildly positive (1956).

That’s basically a 50/50 split. If you consider a bigger sample of all S&P 500 years, historically about two‐thirds or so have ended with a gain, and something close to half have ended with a double‐digit percentage gain. The “streak or no streak” factor may not shift that baseline probability all that much.

In short, there’s a plausible historical precedent for either scenario: about half the time after big multi‐year surges, the index kept rising by 10%+, and half the time it disappointed.

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4. Extra Context: Past Performance Leading Into & After Each Streak

For those who love the raw numbers, below are summary tables showing the 5 years prior to each streak and the 5 years after the break year. This can reveal broader context—whether the market had already been strong or weak before the streak, and how things evolved in the following half‐decade.

A) Example: 1954–1955 Streak

• 5 Years Prior (1949–1953): Averages around +9.5%/yr
• Streak: 1954 (+45%), 1955 (+26%)
• Break Year: 1956 (+2.5%)
• 5 Years After (1956–1960): Averages around +6.3%/yr

You can see that even after those two big 20%+ years ended, the market still had positive average returns in the subsequent five years—but it wasn’t nearly as spectacular as 1954–55.

B) All Seven Streaks: Condensed Table

Here’s a high‐level snapshot for each streak (S&P 500 price returns, approximate):

Streak	Years	Break Year (Return)	5‐Yr Return AFTER	5‐Yr Return BEFORE
1924–25	1924 (+26%), 1925 (+30%)	1926 (+12%)	~+7.2%/yr (1926–30)	−1.4%/yr (1919–23)
1927–28	1927 (+27%), 1928 (+37%)	1929 (−11%)	−11.1%/yr (1929–33)	+17.9%/yr (1922–26)
1935–36	1935 (+47%), 1936 (+34%)	1937 (−35%)	−5.4%/yr (1937–41)	−10.1%/yr (1930–34)
1942–43	1942 (+20%), 1943 (+25%)	1944 (+19%)	+11.5%/yr (1944–48)	−5.4%/yr (1937–41)*
1954–55	1954 (+45%), 1955 (+26%)	1956 (+2.5%)	+6.3%/yr (1956–60)	+9.5%/yr (1949–53)
1995–98 (4‐yr streak)	1995 (+34%), 1996 (+20%), 1997 (+31%), 1998 (+27%)	1999 (+19.5%)	−0.1%/yr (1999–03)	+6.0%/yr (1990–94)
2023–24**	2023 (+24.2%), 2024 (+23.3%)	?? (unknown)	Not yet known	+9.3%/yr (2018–22)

* The 5‐year “before” 1942–43 overlaps the “after” 1935–36.
** Data for 2023 and 2024 as provided (approx. +24.23% and +23.31%, respectively). The break year is undetermined.

From these highlights, you can see how the market environment before and after these big streaks can vary wildly—from the depths of the Great Depression (negative returns for years) to the roaring bubble of the late 1990s.

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5. Final Thoughts & Disclaimers

• Sample Size Caveat: Only 7 multi‐year streaks in about a century is a tiny dataset. That means we should treat any “probability” as at best a light historical reference, not a hard forecast.
• Changing Market Structures: The 1930s to 1950s hardly resemble the globalized, tech‐driven market of the 2020s. Fed policy, globalization, sector composition, and so on differ drastically from past eras.
• Long‐Term Perspective: Even in the historical data, strong short‐term runs do not guarantee that returns must revert sharply. Sometimes they do (e.g., 1929, 1937, 2000–02); other times the market keeps surprising to the upside.

If You’re Watching for Another 20% in 2025

Historically, going for a third consecutive 20%+ year happened only once (the 1990s tech rally). So there’s about a 1‐in‐6 precedent among completed two‐year streaks. On the flip side, there’s about a 50/50 chance that we at least see a +10% year. Again, that’s small‐sample math and not a crystal ball.

Bottom line: If you’re excited by 2023’s and 2024’s stellar performance, it pays to remember the market can do anything in the short run—especially after a couple of big “melt‐up” years. Keep expectations realistic and remember that “history doesn’t repeat, but it often rhymes.”