Flat Betting vs Kelly Criterion: Which Bet Sizing Method Wins Long-Term?
Two bet sizing methods dominate serious betting discussions:
- Flat betting
- The Kelly Criterion
Both are logical.
Both are mathematical.
Only one fits most bettors in the real world.
What Flat Betting Really Is
Flat betting means:
- Same bet size
- Every wager
- Independent of confidence
Usually:
- 1–2% of bankroll per bet
Flat betting assumes:
- You might have an edge
- But you respect uncertainty
- And you prioritize survival
It’s conservative by design.
What the Kelly Criterion Tries to Do
The Kelly Criterion sizes bets based on:
- Your estimated edge
- The odds being offered
The formula attempts to:
- Maximize long-term bankroll growth
- Avoid ruin if inputs are perfect
And that’s the problem.
Kelly Works Only If You Know Your True Edge
Kelly assumes:
- Accurate probabilities
- Stable edges
- Correct pricing
Most bettors:
- Overestimate their edge
- Use small samples
- Confuse variance with skill
A small error in edge estimation leads to massive overbetting.
Why Kelly Feels So Powerful (At First)
Kelly betting often:
- Starts fast
- Grows aggressively
- Produces impressive early curves
This is survivorship bias in action.
You don’t see:
- The blown-up bankrolls
- The unrecoverable drawdowns
- The bettors who quit
Volatility: The Hidden Cost of Kelly
Even correctly applied Kelly betting:
- Produces brutal swings
- Creates deep drawdowns
- Requires extreme emotional discipline
Many bettors abandon Kelly at the worst possible moment — after losses.
At that point, the math no longer matters.
Fractional Kelly: The Compromise
Some bettors use:
- ½ Kelly
- ¼ Kelly
This reduces volatility but introduces a question:
If you’re cutting Kelly down to survive…
Why not just flat bet?
Fractional Kelly slowly converges toward flat betting behavior anyway.
Why Professionals Prefer Flat Betting
Pros value:
- Stability
- Scalability
- Predictable risk
Flat betting allows:
- Clean performance analysis
- Easier automation
- Lower emotional load
- Longer betting careers
Many “Kelly bettors” quietly flatten their bets over time.
Flat Betting Handles Bad Assumptions Better
When your edge estimate is wrong:
- Kelly magnifies the mistake
- Flat betting absorbs it
Flat betting is error-tolerant.
Kelly is not.
The Psychological Reality
Flat betting:
- Reduces tilt
- Prevents chasing
- Keeps losses manageable
Kelly betting:
- Encourages confidence-based sizing
- Amplifies emotional reactions
- Punishes hesitation
Most bettors are human — not equations.
Which One Should You Use?
For most bettors:
- Flat betting wins
- Kelly adds unnecessary risk
- Survival beats optimization
Kelly belongs in:
- Academic models
- Simulations
- Very controlled environments
Flat betting belongs in real bankrolls.
Final Verdict
If your goal is:
- Longevity
- Emotional control
- Sustainable growth
Flat betting is the better choice.
Optimization doesn’t matter if you can’t stay solvent long enough to benefit from it.