KellyIQ

Kelly Criterion Calculator

Put in the odds, your win probability and your bankroll. It shows the Kelly-sized stake at full, half and quarter, and the break-even price the bet has to clear before any of it is worth staking. No login, no email.

Break-even at these odds
52.4%
Your number
55.0%
Edge
+2.6 pts
Full Kelly
$55.00
5.5% of bankroll
Half Kelly
$27.50
2.8% of bankroll
Quarter Kelly
$13.75
1.4% of bankroll

Full Kelly maximizes long-run growth if your probability is exactly right. It never is. Betting a fraction of it keeps most of the growth and cuts the swings hard, which is why most disciplined bettors sit at a half or a quarter.

This sizes one bet under the probability you supplied. It does not estimate that probability, and it does not tell you what to bet. If your number is wrong, the stake is wrong with it.

One bet is the easy case

A calculator sizes a single bet in isolation. A real Sunday is six of them competing for the same bankroll, under a cap on any one position and a cap on the whole day. KellyIQ models the slate as a portfolio: capital split across competing positions, fractional Kelly, per-bet and total exposure limits, and a risk mode that constrains the tail rather than the average.

It also isn’t only about today. Save a slate and the Monte Carlo run shows the distribution of where a bankroll lands rather than a single expected number, which is what makes next Sunday’s card comparable to the ones you have already sized.

A five-position slate in KellyIQ. The Boston Red Sox at -254, the shortest price on the card, receive $50 or 4.4% of the allocation, while the Texas Rangers at -146 receive $400 or 35.5%.
A real slate, half Kelly. The -254 was the shortest price on the card and took $50. The -146 took $400. Sizing follows the edge you assign against the price, not how likely a team is to win, and the whole card used 11.3% of the bankroll rather than all of it.
Size a whole slateHow it works

Common questions

What is the Kelly Criterion?
A formula for how much of a bankroll to stake on a bet, given the odds and your estimate of the win probability. It sizes the bet in proportion to your edge: a bigger edge takes a bigger fraction, and no edge takes nothing.
Why does the calculator sometimes say no bet?
Because the price already demands a higher win probability than you entered. At -110 a bet has to win 52.4% of the time just to break even, so a 52% read is a losing bet and Kelly sizes it at zero. That is the formula working rather than failing.
Should I bet full Kelly?
Full Kelly maximizes long-run growth only if your probability is exactly right, and it never is. Betting a fraction of it keeps most of the growth while cutting the swings sharply, which is why half and quarter Kelly are common. The calculator shows all three so the trade is visible.
Where does the win probability come from?
You supply it. This calculator does not estimate probabilities and does not evaluate whether your number is any good. If the input is wrong, the stake is wrong with it.

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Occasional pieces on sizing, risk and portfolio construction, built from real slates. No picks, no hype.

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KellyIQ is an optimization tool, not a betting service. It produces stakes under assumptions you supply, and makes no claim about whether a bet will win. Nothing here is advice. 21+, US only. If gambling stops being entertainment, call 1-800-GAMBLER.