Library term·Portfolio & valuation
Fractional Kelly Bet Sizing Under Real Market Frictions
Full Kelly vs half/quarter sizing, estimation error tails, autocorrelation and why banks never use textbook Kelly outright.
Authored by·Editorially reviewed
Onur Erkan YıldızFounder, Financial Engineer · CMB-licensed
Higher education in Financial Engineering and Money & Capital Markets. SPK (Turkey CMB) licence. 16 years across institutional markets, research, and quant-driven analytics.
Kelly baseline
Kelly maximises geometric growth under known edge — but markets deliver unknown, drifting edges.Fraction rationale
Industry practice uses fractional Kelly (< 1) to degrade sensitivity to (hat{p}) estimation error.Hidden terms
Costs, autocorrelation, and path constraints shrink effective edge — adjust analytically + stress MC.Finvestopia
We discourage hero leverage narratives — fractional Kelly aligns with tempered risk storytelling.Related entries
Position Sizing
The process of choosing trade size so a single loss does not exceed a defined fraction of capital — typically 0.5–2% per trade.
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Educational content authored by our team — informational only, not investment advice.