Kelly Criterion Betting: How to Size Bets

Kelly Criterion builds on EV betting — read that first if you're new to expected value. Also see our sportsbook guide for which books support sharp bettors.

The Problem With Flat Betting

Most bettors put the same amount on every pick. $100 on a 12% edge underdog. $100 on a 1% edge favorite. Same stake, wildly different risk profiles.

This sounds disciplined, but it's actually broken. Here's why:

If you have a $1,000 bankroll and you're flat-betting $100 on every pick, you can only survive 10 consecutive losses before you're wiped out. On a busy slate — say 15 NCAAB picks in one day during March Madness — you'd need $1,500 in action on a $1,000 bankroll. That's 150% exposure on a single day. One bad Saturday and your bankroll is toast.

There's a better approach, and it's been mathematically proven since the 1950s.

Kelly Criterion in Plain English

The Kelly Criterion is a formula that tells you exactly how much to bet based on how big your edge is. Big edge? Bigger bet. Small edge? Smaller bet. No edge? Don't bet.

The idea is simple: bet proportionally to your advantage. A pick where you have a 7% edge deserves more of your bankroll than a pick where you have a 1.5% edge. Kelly gives you the exact percentages.

The Formula

The Kelly fraction is:

kelly% = (edge) / (odds payout)

Or more precisely: kelly% = (probability × decimal_odds - 1) / (decimal_odds - 1)

But you don't need to do this math. The important thing is the output: a percentage of your bankroll to wager.

At EdgeBets, we use half-Kelly — betting half of what the formula recommends. This sacrifices a small amount of theoretical growth for significantly less volatility. Most professional bettors use fractional Kelly for the same reason.

Real Examples From EdgeBets

Here's how Kelly sizing works with a $1,000 bankroll on two real types of picks:

Pick A: Strong edge on an underdog

Team: +260 moneyline
Our fair odds: +190
EV: +7.3%
Kelly fraction: 3.2%
Bet size: $32 (3.2% of $1,000)

Pick B: Small edge on a slight underdog

Team: +130 moneyline
Our fair odds: +115
EV: +2.1%
Kelly fraction: 0.8%
Bet size: $8 (0.8% of $1,000)

Pick A gets four times the stake of Pick B because the edge is four times larger. If Pick A wins, you collect a meaningful return. If Pick B wins, great — but you didn't risk much on a marginal edge.

Why This Maximizes Long-Term Growth

Kelly Criterion has a mathematical property that no other staking system matches: it maximizes the expected growth rate of your bankroll over time.

Here's the intuition:

Bet too little and you leave money on the table. Your bankroll grows, but slowly.
Bet too much and a losing streak can set you back further than the wins push you forward. Overbetting is the #1 bankroll killer.
Kelly finds the sweet spot — the exact amount that grows your bankroll fastest without excessive risk of ruin.

This is why we use half-Kelly. Full Kelly is theoretically optimal but comes with gut-wrenching swings. Half-Kelly captures about 75% of the growth rate with dramatically smoother results.

Kelly Across a Full Day's Slate

On a typical day, we might post 5-8 picks across NHL, NBA, and NCAAB. Here's what Kelly sizing looks like in practice:

| Pick | Edge | Kelly % | Bet ($1,000 roll) | |------|------|---------|-------------------| | Team A | +8.1% | 3.5% | $35 | | Team B | +5.2% | 2.1% | $21 | | Team C | +3.8% | 1.4% | $14 | | Team D | +2.4% | 0.9% | $9 | | Team E | +1.9% | 0.6% | $6 |

Total exposure: $85, or 8.5% of your bankroll. That's responsible. Even if all five lose, you still have $915 — plenty of bankroll to keep going.

Compare that to flat-betting $100 on each: $500 total exposure, or 50% of your bankroll on one day. That's how accounts blow up.

What Kelly Won't Do

Kelly Criterion doesn't guarantee profits. It doesn't turn losing picks into winners. And it doesn't protect you from a bad run.

What it does is ensure that your bet sizing is mathematically optimal for your edge. Combined with +EV betting — finding bets where the odds are in your favor — Kelly is the best known method for long-term bankroll growth.

How EdgeBets Uses Kelly

Every pick on EdgeBets includes a Kelly fraction. We calculate it from the exact edge (the gap between the offered odds and our consensus fair odds), then apply half-Kelly for safety.

Our Bankroll Tracker shows every bet we've made, the Kelly-sized stake, and the running bankroll balance. We started with $1,000 and track every dollar — wins and losses — publicly.

You can see the math behind every pick on our homepage, including EV%, Kelly%, fair odds, and the number of books in our consensus. For the full methodology, see How It Works.

Every bet on EdgeBets is Kelly-sized. See the results on our Bankroll Tracker and our full Track Record.