Position Sizing
Position Sizing · Portfolio Position Size
How much capital to allocate to a single investment — a decision that affects portfolio outcome as much as stock selection itself.
What it is
Position sizing is the process of determining how large a share of the portfolio to put into a single position. Even an excellent stock pick can hurt the portfolio if the position is too large relative to the rest and the outcome proves wrong; conversely, even a great thesis has little impact if the position is negligible.
Typical inputs into the decision:
- →Conviction — how strong is the investment thesis and how large is the margin of safety
- →Risk — volatility (beta), concentration (exposure), downside scenario
- →Correlation with the rest of the portfolio — does the position add diversification, or does it double an existing risk?
Why track it
Position sizing determines how much a single bad thesis can hurt the portfolio and how much a single good thesis can earn — it is the lever that multiplies the consequences of every individual decision. A disciplined approach to position size protects the portfolio from one wrong bet wiping out the results of dozens of correct ones.
Real-world example
An investor with a strong thesis and a large margin of safety allocates 8% of the portfolio to the position; for an uncertain speculative idea with thin justification they keep the position at 1–2%, even if the potential upside looks attractive — position size reflects the certainty of the thesis, not just the attractiveness of the potential return.
Watch out for
High conviction is not by itself justification for an extremely large position — even well-supported theses sometimes do not materialize. Position sizing should account for the possibility that the investor is wrong, not just the possibility of being right.