Strategy Thesis
Bollinger reversion is one of the oldest mean-reversion playbooks in systematic trading. The logic is straightforward: when price closes below the lower Bollinger band, it has deviated far enough from its rolling mean to warrant a long entry; when it closes above the upper band, the trade is exited. Applied here to a 24-name universe of large-cap US equities spanning tech, financials, healthcare, consumer staples, and energy, the strategy aims to harvest short-term dislocations while staying anchored to names with deep liquidity.
Backtest Overview
Over 451 days the strategy executed 76 trades, compounded to a 17.55% total return (9.46% CAGR), and closed winners on nearly 64% of trades — a respectable hit rate for a systematic strategy. Maximum drawdown came in at 20.57%, which is meaningful but not unusual for an unlevered equity book during a period that included significant macro volatility.
The Sharpe of 0.66 is modest. It suggests the return is real but not particularly risk-adjusted — you are accepting roughly 1.5 units of volatility for every unit of gain. Turnover at 1,720% annualised is high, implying frequent repositioning and sensitivity to transaction costs; the backtest accounts for flat fees but not slippage, which matters at this churn rate.
Walk-Forward Validation: The Key Concern
The validation suite is where the picture complicates. Across four sequential folds the strategy passes a basic profitability test — all four folds are positive — but the trajectory is unmistakably downward:
| Fold | Period | Return | Sharpe | Max DD |
|---|---|---|---|---|
| 1 | Aug 2024 – Jan 2025 | 7.67% | 1.78 | 7.06% |
| 2 | Jan 2025 – Jul 2025 | 1.42% | 0.25 | 20.56% |
| 3 | Jul 2025 – Dec 2025 | 0.77% | 0.20 | 6.66% |
| 4 | Dec 2025 – May 2026 | 0.40% | 0.14 | 11.19% |
Fold 1 looks excellent: 7.67% in five months with a Sharpe of 1.78 and a drawdown under 8%. But returns compress in each subsequent fold, arriving at just 0.40% out-of-sample in the most recent period with a Sharpe of 0.14. The probabilistic Sharpe ratio (PSR) of 0.814 and deflated Sharpe ratio (DSR) of 0.342 — combined with 6 trials tested — indicate a non-trivial probability that the headline Sharpe is inflated by selection bias. The system correctly flags validation as failed.
Recent Live Activity
Deployed on 31 May 2026 with a $10,000 paper allocation, the strategy opened four positions immediately: WMT, COST, GOOGL, and PG — defensive and consumer-oriented names, consistent with its reversion logic firing during a softer tape. On 1 June it executed two more buys; the following two daily runs each saw one signal rejected, suggesting either position-size constraints or the portfolio approaching full allocation. Current paper NAV sits at $9,956.56 against a $10,000 starting balance — essentially flat in its first few days, which is neither alarming nor encouraging at this sample size.
Strengths and Risks
Strengths: Conceptually sound and transparent. The universe is liquid, the logic is rules-based with no ambiguity, and the 64% win rate over 76 trades provides a credible sample. All four walk-forward folds were profitable, which is more than most strategies can claim.
Risks: The fade in edge across folds is the dominant concern. Whether this reflects regime change, crowding in classic band-reversion signals, or simply the absence of the volatile early-2024 setup that made Fold 1 exceptional is unclear. At a DSR of 0.34, there is a meaningful chance the strategy's edge is weaker than the backtest implies. High turnover also means live performance will be sensitive to execution quality and spread costs that flat-fee assumptions do not capture.
This is a strategy worth watching in paper mode, but not one to size aggressively until the live out-of-sample record accumulates.