Kalshi 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.
Put disciplined sizing on autopilot
Bot for Kalshi builds the half-Kelly logic, position limits, and risk controls straight into your bots — so every trade is sized the way this calculator recommends, automatically.