Risk management: position size, stop and drawdown

Why risk comes first

Losses are asymmetric. After losing 10% you need a gain of 11.1% to recover; after losing 50% you need 100%. The deeper the drawdown, the steeper the road back, which is why limiting each loss matters more than finding a perfect entry.

Position sizing

A common framework fixes a small percentage of the account to risk per idea, often cited between 0.5% and 2%, and derives the size from the distance to the invalidation level.

Size = (account × risk %) / |entry − stop|

Example: an account of 10,000, risking 1% (100), with an entry at 50 and a stop at 48. The distance is 2, so the size is 100 / 2 = 50 units. The size is determined by the stop, not by conviction.

Where a stop goes

A stop-loss is a predefined level at which the idea is considered invalid. It is generally placed beyond a level that would not be reached if the analysis were right, such as past a support, and often with room expressed in ATR multiples so that normal noise does not trigger it. Placing it by the amount you are willing to lose, instead of by the market, tends to produce stops in meaningless places.

Stops are not guaranteed: gaps and fast markets can cause execution beyond the stop level.

Risk-reward and win rate

Risk-reward = potential gain / potential loss
Break-even win rate = 1 / (1 + risk-reward)

With a risk-reward of 2, a method needs to win only a third of the time to break even before costs. A risk-reward of 0.5 needs two wins out of three. Neither is better in itself; what matters is the combination and the costs.

Common mistakes

• Moving a stop further away after the price approaches it.
• Adding to a losing position to “average down”.
• Using leverage that makes a normal move large enough to wipe out the account.
• Concentrating everything in one asset or in highly correlated ones.

InvestAI never places orders or holds funds: its readings and synthesis are information, and this guide is a learning resource, not investment advice. Investing carries a risk of capital loss.