Choosing a staking strategy
You have done the hard work: found a system, identified edges, and built a bankroll. Now comes a question that will quietly determine a huge portion of your results: how much should you bet on each wager? The two most common answers are flat betting and the Kelly Criterion, and they represent fundamentally different philosophies about risk, growth, and simplicity.
Neither is universally superior. The right choice depends on your experience level, your confidence in your probability estimates, and your psychological tolerance for drawdowns. Let us break down both approaches with real numbers so you can make an informed decision.
Flat betting: simplicity and safety
Flat betting means wagering the same fixed amount on every bet, regardless of your perceived confidence in the outcome. If your unit is $20, every bet is $20 — whether you see it as a strong play or a marginal edge.
The primary advantage is simplicity. There are no calculations to make, no subjective confidence ratings to assign, and no risk of catastrophically overbetting on a play where your edge estimate is wrong. Flat betting also produces the smoothest equity curve: your bankroll grows (or shrinks) in small, predictable increments.
• Zero complexity — no formulas, no subjective inputs
• Lowest variance of any staking method
• Psychologically easy to follow during losing streaks
• Immune to errors in probability estimation
Cons of flat betting:
• Does not capitalize on higher-edge opportunities
• Slower bankroll growth compared to variable staking
• A $20 bet on a 10% edge play and a 2% edge play is not capital-efficient
Kelly Criterion: mathematically optimal growth
The Kelly Criterion is a formula developed by John Kelly at Bell Labs in 1956. It calculates the optimal fraction of your bankroll to wager based on your estimated edge and the odds offered. The goal is to maximize the long-term growth rate of your bankroll.
f* = (bp − q) / b
Where:
f* = fraction of bankroll to wager
b = decimal odds minus 1 (the net payout per dollar wagered)
p = your estimated probability of winning
q = your estimated probability of losing (1 − p)
Example: Odds of 2.20, estimated 50% win probability.
b = 1.20, p = 0.50, q = 0.50
f* = (1.20 × 0.50 − 0.50) / 1.20 = 0.10 / 1.20 = 8.3% of bankroll
Kelly is mathematically proven to maximize the geometric growth rate of your bankroll over time, assuming your probability estimates are accurate. It naturally bets more on high-edge situations and less (or nothing) on low-edge or no-edge situations.
• Maximizes long-term growth rate (mathematically proven)
• Automatically sizes bets proportional to your edge
• Naturally avoids overbetting when edge is small
• Bets zero when there is no edge
Cons of Kelly:
• Requires accurate probability estimates (the hardest part of betting)
• Full Kelly produces extremely high variance
• Overestimating your edge by even a small amount leads to systematic overbetting
• Psychologically demanding during drawdowns
The problem with full Kelly
In theory, full Kelly is optimal. In practice, it is dangerously aggressive for almost everyone. The reason is simple: the formula assumes your probability estimates are perfectly calibrated. They never are.
If you estimate a 55% probability but the true probability is 52%, full Kelly will have you betting significantly more than the actual optimal amount. Over time, this systematic overbet erodes your bankroll instead of growing it. The formula is extremely sensitive to input accuracy.
Additionally, full Kelly produces gut-wrenching drawdowns. Simulations show that a full Kelly bettor will typically experience a 50% drawdown from peak at some point, even with a genuine edge. Most humans cannot sit through that without abandoning their strategy.
Fractional Kelly: the practical middle ground
Most experienced bettors who use Kelly employ a fractional version — typically quarter Kelly (25%) or half Kelly (50%). This means you calculate the full Kelly stake and then bet only a fraction of it.
- Quarter Kelly (25%): Very conservative. Growth is slower but drawdowns are small and manageable. Best for bettors who are uncertain about the accuracy of their probability estimates.
- Half Kelly (50%): The most common choice among professional bettors. It sacrifices only about 25% of the growth rate compared to full Kelly while cutting drawdowns roughly in half. A good balance of growth and safety.
- Three-quarter Kelly (75%): More aggressive. Only appropriate if you have strong confidence in your probability estimates, typically backed by a proven model with a long track record.
For a more detailed look at the Kelly Criterion, unit sizing, and other bankroll concepts, see our bankroll management guide.
Which should you choose?
Here is a practical decision framework:
- Choose flat betting if: You are relatively new to sports betting, you do not have a statistical model generating probability estimates, you prefer simplicity, or you find drawdowns stressful.
- Choose fractional Kelly if: You have a model or methodology that produces probability estimates you trust, you understand that drawdowns will be larger, and you want to maximize growth over the long run.
- Never use full Kelly unless you are running a quantitative operation with rigorously backtested probability models and you have deep experience managing variance.