Kelly Criterion & Flat Betting Guide
While progression systems fail mathematically, two approaches stand on a different foundation: flat betting (the honest baseline) and the Kelly Criterion (the only mathematically optimal staking system — but only when EV is genuinely positive).
Flat Betting: The Honest Baseline
Flat betting means wagering the same amount on every bet. No progressions, no doubling, no sequences. It is the simplest possible staking plan.
Compared to Martingale or Fibonacci, flat betting has the same expected value (negative in casino games) but dramatically lower variance. You will not win big — and you will not lose catastrophically in a single session either.
Flat Betting Advantages
• Predictable session cost (bankroll × house edge)
• No runaway losses from bad streaks
• No table limit issues
• Easy bankroll management
vs. Progression Systems
• Same or lower total expected loss
• Lower variance — fewer extreme outcomes
• No illusion of a "system" that works
• Cannot hit table limits
How to Use the Flat Betting Calculator
- 1.Enter your bet size and bankroll. The ratio matters — a $10 flat bet on a $200 bankroll gives you 20 bets. A $5 bet gives you 40.
- 2.Set win probability and house edge. Match these to a real game to see an honest projection of your session costs.
- 3.Run simulations. Compare the distribution to Martingale. Note how flat betting produces far fewer total wipeouts — but the average outcome is similar.
The Kelly Criterion: Optimal Sizing for Positive EV
The Kelly Criterion is a mathematical formula for determining the optimal fraction of your bankroll to bet when you have a genuine edge (positive expected value). It maximises the long-term geometric growth rate of your bankroll.
Kelly Formula
f* = (bp − q) / b
- f* = fraction of bankroll to bet
- b = net odds received on the bet (e.g., 2.0 = 2:1)
- p = probability of winning
- q = probability of losing (1 − p)
Example: Sports Bet with a Real Edge
A bookmaker offers 2.10 odds (decimal) on a team you believe has a 55% true chance of winning.
- b = 1.10 (net odds — you win $1.10 per $1 bet)
- p = 0.55 (your estimated probability)
- q = 0.45
Kelly says bet 14.1% of your bankroll on this outcome.
Critical Warning
Kelly only produces positive results when your estimated probabilities are accurate and your EV is genuinely positive. In casino games (where the house has the edge), Kelly always returns a negative bet fraction — meaning do not bet at all. Applying Kelly to a negative-EV game does not make it profitable.
How to Use the Kelly Criterion Calculator
- 1.Enter your estimated win probability. This is your own assessment of the true probability, not the odds implied by the bookmaker.
- 2.Enter the decimal odds (or payout). A 2.0 decimal odd pays $1 profit per $1 wagered (plus your stake back). A 3.0 odd pays $2 profit.
- 3.Enter your total bankroll. The Kelly output is a fraction — multiply by bankroll to get the dollar amount to bet.
- 4.Consider fractional Kelly. Full Kelly maximises growth but produces high variance. Many professionals use half-Kelly (bet half the recommended amount) to reduce drawdowns while maintaining strong growth.
- 5.If the result is zero or negative, the bet has no edge. Do not bet.
Kelly vs. Flat Betting vs. Martingale
| System | Works when EV > 0? | Works when EV < 0? | Variance |
|---|---|---|---|
| Kelly Criterion | Yes — optimal | No | Moderate |
| Flat Betting | Suboptimal but safe | No | Low |
| Martingale | No | No | Very high |
| Fibonacci | No | No | High |
Try the Calculators
See flat betting as a baseline and calculate Kelly sizing for your bets.