Bot for KalshiKalshi Kelly Calculator
Enter your own probability estimate against the market price and get the mathematically optimal position size — full Kelly, the practical half and quarter-Kelly stakes, expected value, and long-run log-growth. Pure math, no account needed.
| Sizing | Fraction | Stake | Log-growth |
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This is a math tool, not financial advice. The hard part is your probability estimate — Kelly is only optimal if it is right, and overconfidence over-bets toward ruin. That is exactly why half and quarter-Kelly exist.
How the Kelly criterion works on Kalshi
A Kalshi YES contract at price c¢ risks c to win (100 − c). The net payout ratio is b = (100 − c) / c, and the full-Kelly fraction of your bankroll is:
f* = p − q / b
p = your estimated probability of YES
q = 1 − p
b = (100 − c) / cIf f* is zero or negative, your probability does not beat the price — there is no positive-edge stake, so the calculator says do not bet rather than sizing down to a tiny number.
Why half-Kelly is the practical default
Full Kelly maximizes theoretical growth but assumes your probability is exact and tolerates brutal drawdowns. Half-Kelly keeps roughly 75% of the growth rate with substantially smaller swings and far more tolerance for estimation error — which is why nearly every quantitative trader and bot sizes with a fractional Kelly. This tool highlights the half-Kelly row as the recommended default for that reason.
For the full derivation, drawdown math, and practical caps, read the in-depth Kelly criterion for Kalshi guide, or see the broader Kalshi trading strategies guide.
Turn the sizing decision into explicit limits
Bot for Kalshi lets you define position and loss controls around a rule you have reviewed. It does not estimate your probability or automatically apply Kelly sizing; use this calculator to choose the limit, then encode and paper-test it deliberately.