Kelly size is a half-Kelly bet fraction from historical win rate and risk/reward; recommended size further scales it by confidence and a portfolio cap.
f* = (p·b − q) / b, where p is historical win rate, q = 1−p, and b is average win divided by average loss. We use half of the full Kelly output — full Kelly is growth-optimal in theory but produces punishing swings in practice; half-Kelly gives up a modest amount of long-run growth for a large reduction in variance.
Live example: AAPL's current Kelly size is 7.0%, and the final recommended position size (after the confidence multiplier and portfolio cap) is 0.4%. See the full AAPL forecast for the trade plan this sizing attaches to.
Recommended position size scales Kelly size down further by the signal's model confidence, and caps it at a hard portfolio limit (default 10% per position). Direction without sizing discipline loses money over time — two traders can agree on the same BUY call and have completely different outcomes purely from how much capital each risked.
Full Kelly is growth-optimal in theory but produces large, hard-to-tolerate drawdowns in practice. Half-Kelly gives up modest growth for much lower variance.
A 0% reading means the Kelly formula found no positive edge for that ticker's current win rate and risk/reward — not a system error.
Kelly size is the raw half-Kelly output; recommended size scales it down further by model confidence and caps it at a hard portfolio limit.
AAPL analysis shows this metric in context, or browse all S&P 500 tickers.
Educational research only — not investment advice.