"Use a 7% stop loss." You've heard this. It's in every IBD summary, every breakout trading article. And it's not wrong — but it's incomplete in a way that costs traders money.
Here's what the full methodology actually says, what we validated across 36 years of Thai data, and why the number matters less than where you place it.
The Real Purpose of a Stop Loss
A stop loss is not a "safety net" you set and forget. It's the defining element of your position size.
The correct sequence is: 1. Identify where the trade is wrong (a price level that invalidates the setup) 2. Calculate the distance from entry to that level (your risk per share) 3. Size your position so that distance × shares = your maximum acceptable loss (e.g. 0.25% of portfolio)
The stop comes first. The position size follows from it. Most traders do it backward — they decide how many shares to buy, then think about a stop. That's why they get hurt.
Why "7%" Is a Starting Point, Not a Rule
In O'Neil's methodology, 7–8% below your entry is the outer limit. It's a ceiling, not a target. The actual stop should be set at a technically meaningful level — typically the low of the most recent consolidation or handle.
The distinction matters: - If the pivot is at ฿100, the recent base low is ฿96, and you enter at ฿100.50 → your stop is at ฿95.50 (base low minus a small buffer). Risk = 4.97%. The 7% rule doesn't apply — the chart dictates. - If the base is sloppy and the low is ฿92 → entry ÷ low = 8.7% → this setup is too risky at standard position size. Skip it or size down significantly.
The 7% rule is a circuit breaker for when you can't find a clean technical level. It's the maximum tolerance, not the ideal placement.
What the Chart Tells You (Risk Map Thinking)
We describe charts as risk maps, not prediction machines. The stop location is the most important decision you make on any trade — not the entry, not the target.
A high-quality stop has these properties: - Placed at a level where the setup is unambiguously broken (not just "pulled back a bit") - Far enough below the pivot that normal volatility won't shake you out - Close enough that if it does trigger, the loss is contained
In Thai stocks, we found that the stop at the base low (specifically: the lowest close of the handle or the most recent pullback) outperformed arbitrary percentage stops consistently. The market "knows" those levels — they're where buyers entered and where the setup proves itself wrong.
The Position Size Equation
Once you have a stop distance, position sizing is mechanical:
`
shares = (portfolio × risk%) ÷ (entry price − stop price)
`
Example (฿1M portfolio, 0.25% risk per trade): - Entry: ฿100.50 - Stop: ฿95.50 (risk per share: ฿5.00) - Max loss target: ฿1,000,000 × 0.25% = ฿2,500 - Shares: ฿2,500 ÷ ฿5.00 = 500 shares
If the stop triggers, you lose ฿2,500 (0.25% of portfolio). Manageable. You can absorb a string of losses and stay in the game.
At 2% risk per trade with the same setup, you'd hold 4,000 shares. A stop-out costs ฿20,000. Several consecutive losses at that size and you're psychologically compromised before the next trade. Our 36-year simulation confirmed this: 2% risk per trade reduced long-term returns compared to 0.25–0.5% because the drawdowns compounded faster than the gains.
What We Found in Thai Data
After testing across all Thai stocks from 1990–2026:
- Stops at the base low outperformed fixed % stops in most regime conditions
- The 7% hard limit is appropriate only when the base is wide or the structure is unclear
- Stops tighter than 3% (except in very tight VCP-style formations) got triggered by normal intraday noise too often, hurting expectancy
- The quality of the stop determines the quality of the trade — a setup with a natural, clean stop is worth more than the same entry with a forced, arbitrary stop
This is why we don't just filter by entry conditions. We rate the setup by the quality of the stop that comes with it. A great entry + unclear stop = pass. A clean stop + decent entry = worth taking.
Practical Checklist Before Any Trade
Before entering, answer these three questions:
1. Where exactly is my stop? (Specific price, not "around 7%") 2. Given that stop, what is my position size to risk 0.25%? 3. Is that stop at a level that clearly invalidates the setup, or just an arbitrary number?
If you can't answer all three precisely, the trade isn't ready.
Personal research. Not investment advice. Backtests run on Thai stocks 1990–2026 with transaction cost assumptions.
[Download the free 36-year research brief →](https://moeasymmetry.netlify.app/the-36-year-test.html)