Kelly criterion calculator
Enter your estimated win probability, the contract price in cents and your bankroll. The calculator sizes a Kelly stake after Kalshi’s fee and lets you scale it down to a fractional Kelly.
How it works
The Kelly criterion sizes a stake to grow a bankroll fastest when your probability estimate is right. It bets nothing when the price is above your probability, and more as the edge grows.
Full Kelly is aggressive and very sensitive to errors in your estimate. Most traders use a fraction, such as a quarter Kelly. If your probability comes from a sportsbook fair value, remember that the fair value is itself an estimate.
Common questions
What is the Kelly formula for a $1 contract?
With price c (including fees) and win probability p, the net odds are b = (1 − c) ÷ c and the Kelly fraction is (b × p − (1 − p)) ÷ b.
Why use fractional Kelly?
Probability estimates are uncertain. A fraction of Kelly gives up some growth in exchange for much smaller drawdowns when your estimate is wrong.
Does the calculator include fees?
Yes, optionally. Choose Kalshi to add its per-contract taker fee to the price before sizing.
What if Kelly says zero?
The price is at or above your probability after fees, so there is no positive expected value at that price.