A stop is an execution mechanism; invalidation is the reasoning
A stop-loss can automatically trigger an order when a specified condition is reached. But the more important concept is the invalidation level: the price or event at which the original reason for holding the position is no longer valid.
Three different ideas people mix together
Stop price: the trigger condition. Execution price: the price actually obtained. Thesis invalidation: the evidence that says the position should no longer be held. They can be related without being identical.
Worked position-sizing example
You have ₹1,00,000 of capital and are willing to risk ₹2,000 on a trade. Entry is ₹500 and planned invalidation is ₹480, so risk per share is ₹20. A simplified risk-based size is 100 shares. This is a sizing calculation, not a guarantee that the loss will be exactly ₹2,000.
Why stops can fail to protect the exact price
- Overnight gaps can jump across the trigger.
- Fast markets can produce slippage.
- Thin liquidity can make execution difficult.
- Order-type rules differ by venue and broker.
Percentage stops versus structure stops
A fixed 5% stop treats every stock as if it has identical volatility and structure. A structure-based invalidation can be tied to a broken support area, failed breakout or changed thesis. Volatility-adjusted methods can also be used, but every method should be tested against the strategy's actual behaviour.
Common mistakes
- Placing a stop so close that normal noise repeatedly triggers it.
- Moving the stop farther away simply to avoid taking a loss.
- Using a stop without reducing position size when the stop is wider.
- Assuming a stop guarantees the planned loss.
Checklist
- Why am I entering?
- What proves the thesis wrong?
- Where is the invalidation?
- What is the rupee risk?
- What size matches that risk?
- What happens if the stock gaps?