Mean reversion · daily rule · Software & devices
Bollinger Reversion on Fortinet
What the play says
FTNT with the play, last two years
Shading shows the play's call from the close that triggered it.
Growth of $10,000 since 2009
Log scale. After trading costs, with T-bill interest while out.
The record
The play against buying and holding FTNT over exactly the same dates, after costs.
| Play, since 2009 | Hold, since 2009 | Play, 5 yrs | Hold, 5 yrs | |
|---|---|---|---|---|
| Annual return | +7.0% | +32.1% | +10.9% | +25.3% |
| Total return | +209% | +10,527% | +67% | +208% |
| Worst drawdown | −42.1% | −51.2% | −30.7% | −38.3% |
| Volatility | 22.0% | 41.5% | 26.6% | 44.7% |
| Sharpe ratio | 0.35 | 0.84 | 0.38 | 0.65 |
| Time invested | 20% | 100% | ||
| Switches per year | 7.5 | 0 |
Every call, graded
Right on 77 of 126 closed calls (61%). In calls averaged +2.0%; out calls saw FTNT move +7.5% on average.
| Called | Call | Price | Until | FTNT moved | Result |
|---|---|---|---|---|---|
| Apr 16, 2026 | OUT | $82.40 | now | +131.5% | open |
| Apr 10, 2026 | IN | $76.70 | Apr 16, 2026 | +7.4% | ✓ right |
| Apr 2, 2026 | OUT | $82.53 | Apr 10, 2026 | −7.1% | ✓ right |
| Mar 27, 2026 | IN | $78.20 | Apr 2, 2026 | +5.5% | ✓ right |
| Mar 3, 2026 | OUT | $81.10 | Mar 27, 2026 | −3.6% | ✓ right |
| Feb 23, 2026 | IN | $75.60 | Mar 3, 2026 | +7.3% | ✓ right |
| Jan 23, 2026 | OUT | $81.64 | Feb 23, 2026 | −7.4% | ✓ right |
| Jan 14, 2026 | IN | $76.39 | Jan 23, 2026 | +6.9% | ✓ right |
| Dec 1, 2025 | OUT | $81.82 | Jan 14, 2026 | −6.6% | ✓ right |
| Nov 6, 2025 | IN | $80.54 | Dec 1, 2025 | +1.6% | ✓ right |
| Sep 5, 2025 | OUT | $78.83 | Nov 6, 2025 | +2.2% | ✕ wrong |
| Aug 1, 2025 | IN | $97.36 | Sep 5, 2025 | −19.0% | ✕ wrong |
An in call is right when the price rose before the next call; an out call is right when it fell. The latest 12 of 127 calls shown.
How the play works
- In on a close below the lower band (20-day average − 2 standard deviations).
- Out on a close above the 20-day average.
This runs against Bollinger's advice that tags of the bands are not signals. It is shown because so many traders use it.
The case against
Valeriy Zakamulin tested moving-average timing on up to 155 years of U.S. stock data and found no statistically significant edge in the second half of that record. The rules earned their keep in a few severe bear markets and lagged buy and hold for long stretches in between.