Tool · Discipline · Three Modes

Bankroll
calculator.

The single most important calculation in sports betting: how much should you risk on this bet? Three modes — flat staking, percentage of bankroll, and Kelly Criterion — for the disciplined SA bettor who wants to keep their bankroll alive.

Calculator

Optimal bet size

Choose your sizing methodology, then enter the inputs.

Enter your bankroll to see recommended bet size

The three modes, compared

Flat staking

Same Rand amount on every bet. Simple, predictable, low variance. Doesn't compound winning runs. Doesn't reduce stakes during losing runs. Best for new bettors who want to develop discipline before optimising. Standard recommendation: 1-2% of starting bankroll per bet.

Percentage staking

Fixed percentage of current bankroll. Self-adjusts: stakes grow with winning runs, shrink with losing runs. The most common professional approach. Standard recommendation: 1-3% per bet, 2% as default.

Kelly Criterion

Optimal bet size based on perceived edge. Calculated as: Kelly% = (b·p − q) ÷ b, where b = decimal odds − 1, p = your estimated win probability, q = 1 − p. Theoretically maximises long-term bankroll growth — but requires accurate edge estimation, which most bettors lack. Use fractional Kelly (0.25 to 0.5 of full Kelly) to absorb estimation errors.

The honest recommendation

For most SA bettors, simple percentage staking at 2% per bet is the right answer. It's mathematically sound, psychologically manageable, and doesn't require you to estimate your edge precisely (which most bettors do badly). Kelly is for bettors who track every result over hundreds of bets and have empirical evidence of edge. Flat staking is for absolute beginners or for fixed-stake disciplines like accumulator betting.

Why position sizing matters more than picking winners

A bettor with a 55% win rate at even-money odds (2.00) has a clear edge. They'll be profitable over time. But if they bet 20% of bankroll on each pick, a normal 6-bet losing streak (which has roughly a 1-in-100 probability) blows up two-thirds of their bankroll. Variance kills bankrolls long before the underlying edge has time to manifest.

Same bettor at 2% per bet survives 6-bet streaks easily — only 12% of bankroll lost in the worst case, plenty left to recover. Position sizing isn't a mathematical optimisation game. It's survival.

* Bets until bust is a worst-case estimate based on losing every bet at the recommended size. Real losing streaks are much shorter than this — but the figure illustrates how aggressive sizing erodes survival capacity.

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Common Questions

You asked.

Flat staking: same fixed Rand amount on every bet (e.g. R100 each time). Simple, low variance, doesn't adapt to bankroll changes. Percentage staking: a fixed percentage of current bankroll (e.g. 2%). Self-adjusts as bankroll grows or shrinks. Kelly Criterion: dynamic bet sizing based on perceived edge — bigger bets on high-edge plays, smaller on marginal ones. Theoretically optimal but requires accurate edge estimation and produces high variance.

Money you can afford to lose entirely without affecting essential expenses. For sports betting at 1-2% per bet, you want at least 50 units of bankroll — meaning if your typical bet is R100, your bankroll should be R5,000+. Smaller bankrolls force smaller bets, which is fine but less rewarding. Never bet borrowed money, money earmarked for bills, or money you'd need back.

Full Kelly is mathematically optimal but psychologically brutal — drawdowns of 50%+ are normal. Most professional bettors use 1/4 Kelly (quarter Kelly) which dampens variance significantly while retaining most of the growth. For recreational SA bettors who don't track edge precisely, 1/4 Kelly or simple flat percentage staking (1-2% per bet) is more practical than self-estimated Kelly.

Honest answer: most bettors don't, even when they think they do. Edge = your estimated probability minus the bookmaker's implied probability. If you think a team wins 55% of the time and the bookmaker prices at odds of 2.00 (50% implied), your edge is 5%. The catch is that 'your estimated probability' is usually overconfident. The discipline is to underweight your own estimates — assume you're less right than you feel — and use fractional Kelly to absorb the inevitable estimation errors.