The Narrative vs. The Data
Ask any experienced trader about mid-August and you'll hear the same warnings: thin summer markets, volatility spikes, flash crashes. The conventional wisdom is clear — the second half of August is dangerous, and the prudent move is to reduce exposure and wait for September.
The data says something more nuanced.
Over 16 years of /ES continuous front-month data (Aug 16–31, 2010–2025), the second half of August has closed higher 11 of 16 times — a 68.8% win rate. The average return is essentially flat at +0.01%, held down by two catastrophic outliers that dominate the narrative.
The Numbers
| Year | Period | Return | Max Up | Max Down |
|---|---|---|---|---|
| 2010 | Aug 16 – Aug 31 | -2.34% | +2.00% | -3.68% |
| 2011 | Aug 16 – Aug 31 | +1.73% | +2.58% | -3.63% |
| 2012 | Aug 16 – Aug 31 | +0.07% | +1.50% | -0.68% |
| 2013 | Aug 16 – Aug 30 | -1.36% | +0.79% | -2.15% |
| 2014 | Aug 18 – Aug 29 | +2.20% | +2.46% | 0.00% |
| 2015 | Aug 17 – Aug 31 | -5.93% | +0.67% | -12.80% |
| 2016 | Aug 16 – Aug 31 | -0.80% | +0.25% | -0.85% |
| 2017 | Aug 16 – Aug 31 | +0.24% | +0.40% | -1.10% |
| 2018 | Aug 16 – Aug 31 | +3.00% | +3.36% | -0.53% |
| 2019 | Aug 16 – Aug 30 | +2.55% | +3.36% | -3.80% |
| 2020 | Aug 17 – Aug 31 | +3.80% | +4.71% | -0.63% |
| 2021 | Aug 16 – Aug 31 | +1.61% | +1.93% | -1.67% |
| 2022 | Aug 16 – Aug 31 | -7.78% | +1.57% | -8.56% |
| 2023 | Aug 16 – Aug 31 | +1.44% | +2.00% | -1.76% |
| 2024 | Aug 16 – Aug 30 | +1.58% | +1.87% | -0.78% |
| 2025 | Aug 18 – Aug 29 | +0.11% | +0.86% | -1.69% |
The Two Events That Built the Narrative
The entire bearish reputation for mid-August rests almost entirely on two years:
2015 (-5.93%, max drawdown -12.80%): China devalued the yuan on August 11. The move sparked a global emerging markets selloff. August 24, 2015 — "Black Monday" — saw /ES gap down nearly 100 points at the open. The S&P hit circuit breakers intraday. This was not seasonal weakness; it was a specific geopolitical event that happened to fall in August.
2022 (-7.78%): Jerome Powell's Jackson Hole speech on August 26, 2022 was the most hawkish Fed communication in decades. "Restoring price stability will likely require maintaining a restrictive policy stance for some time." The market had priced in a pivot; Powell explicitly rejected it. The 3.4% single-day loss on August 26 accounts for nearly all of 2022's August 2nd half return.
Remove those two macro shocks, and the remaining 14 years show an average return of +1.02% with a 78.6% win rate.
Why the Narrative Persists
The 2015 and 2022 crashes were violent and memorable. Traders who lived through the Black Monday gap or the Jackson Hole dump carry a visceral risk aversion toward mid-August. That's psychologically understandable and narratively compelling — but it doesn't describe the base rate.
There's also a structural argument that gets recycled: thin summer markets amplify moves, so the downside is worse. That's true as a statement about volatility — but volatility cuts both ways. The same thin conditions that let 2015 and 2022 gap lower also let 2018, 2019, and 2020 drift cleanly higher.
The Honest Read
The base rate is bullish (68.8% win). The average return is flat (+0.01%). The tail risk is real but concentrated in two macro-event years.
The correct framing is not "August second half is bearish" — it's "August second half has fat tails." The distribution is wider than other months. If you're sizing for a normal month and a 2015-type event hits, you're underestimating the damage. If you're hiding in cash every August second half to avoid a repeat of 2015, you've missed 11 of the last 16 positive periods.
The answer is position sizing for the tail, not avoidance.
Summary
| Metric | Value |
|---|---|
| Sample | 2010–2025 (16 years) |
| Win rate | 68.8% (11 of 16) |
| Avg return | +0.01% |
| Avg max drawdown | -2.88% |
| Ex-2015 and 2022 | Avg +1.02%, win rate 78.6% |
| Worst year | 2022: -7.78% (Jackson Hole) |
| Best year | 2020: +3.80% |
The August second half bear narrative is built on two specific macro events. The base rate says buy the dip, size for the tail risk.