Ask most punters how they land on a stake and you'll usually get a shrug. A tenner here, fifty on the "good thing" there, maybe double up after a bad run to "get it back". Bet sizing is the part of punting almost nobody studies properly — and it's exactly the gap this video sets out to fill, walking through the Kelly Criterion: a formula built specifically to answer the question "given an edge, how much should I actually risk?"
Where the formula comes from
The Kelly Criterion isn't a betting gimmick — it was developed in 1956 by John L. Kelly Jr., a scientist at Bell Labs, originally to solve a problem in information theory about long-distance telephone signal noise. Gamblers and later Wall Street quants picked it up because the underlying maths translates neatly to any situation involving repeated bets with an edge, from blackjack card counting to horse racing to hedge fund position sizing.
The formula itself, as the video explains, is straightforward in form even if the thinking behind it isn't: your optimal stake is a function of your edge and the odds on offer. Get a bigger edge at generous odds, and the formula tells you to bet more of your bankroll. A marginal edge at short odds, and it tells you to bet next to nothing. The elegant bit is that Kelly doesn't just try to win — it's designed to maximise the long-run growth rate of a bankroll across many bets, rather than chasing the biggest single result.
Why "full Kelly" scares serious bettors
Here's the catch the video spends real time on, and it's the most important takeaway for anyone tempted to plug numbers into a Kelly calculator: full Kelly assumes your probability estimate is exactly right. It almost never is. Shade your true win chance by even a few percentage points — entirely plausible when you're setting your own prices on a horse race — and full Kelly can tell you to stake several times more than it should. The result is brutal volatility: extended losing runs, savage drawdowns, and for an overconfident bettor, a real risk of blowing up a bankroll even while holding a genuine edge.
That's why almost nobody who uses Kelly seriously bets "full Kelly" in practice. Half Kelly, quarter Kelly, or even smaller fractions are the norm, deliberately sacrificing some theoretical growth for a much smoother, more survivable ride. It's a sensible hedge against the fact that human edge estimates are noisy, not gospel.
Why it matters for punters
For Australian racing bettors, the lesson isn't "go calculate Kelly stakes for Saturday's card" — it's the mindset shift underneath it. Bookmaker overround means the market price rarely equals the true probability, so any "edge" a punter thinks they have is an estimate, not a fact. Treating stake size as seriously as selection — and staying sceptical of your own confidence — is what separates punters who survive variance from those who get wiped out by one bad month. Betting is inherently risky, and no staking method removes that; understanding the maths just makes the risk a conscious choice rather than an accident.
Betting 101 at The Daily Punt, covering Australian racing and sport with an eye for where the value sits.
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