Glossary / Portfolio

Position Sizing

Position sizing is the process of deciding how much capital to allocate to one stock, ETF, or trade idea. It connects your thesis to your portfolio risk.

Why it matters

Two investors can have the same view on a stock but very different outcomes because their sizing differs. A strong idea sized too large can damage a portfolio if the thesis fails. A small position in a volatile name may be easier to hold through normal price movement.

What affects position size

• Downside level: how much could be lost before the thesis is invalidated.
• Volatility: how wide normal price swings are for the asset.
• Conviction: how strong the evidence is, not how exciting the story feels.
• Correlation: whether the idea behaves like positions you already own.
• Liquidity: how easily the position can be adjusted or exited.

Research habit

Think about position sizing before entering, not after the price moves. The sizing decision should fit the research plan, the stop or invalidation rule, and the investor's broader portfolio constraints.