1. The Three Main Formats
South African bookies generally offer the choice between three different ways to display odds:
- Decimal (e.g., 2.50): The most common in SA. It represents the total return for every R1 wagered, including your stake. (A R10 bet at 2.50 returns R25).
- Fractional (e.g., 6/4): Traditional format. It shows profit relative to stake. You win R6 for every R4 wagered. (A R10 bet returns R15 profit + R10 stake = R25).
- American (e.g., +150): Rarely used here, but good to know. A "+" number shows profit on a R100 bet. A "-" number shows how much you must bet to win R100.
2. Implied Probability
Odds are just bookmakers translating probabilities into numbers. To calculate the implied probability of decimal odds, use the formula: (1 / Decimal Odds) * 100.
For example, odds of 2.00 imply a 50% chance of winning (1 / 2.00) * 100 = 50%. If you do your research and believe the true chance of the event happening is 60%, then betting at 2.00 represents a Value Bet.
3. The Bookmaker's Margin (The Vigorish)
If you calculate the implied probabilities for all possible outcomes in a match (e.g., Team A wins, Team B wins, Draw) and add them together, the total will always be greater than 100% (usually 105% to 110%).
That extra percentage is the "margin" or "vig". It's the bookmaker's built-in profit margin. To be a profitable bettor long-term, your strategy must be good enough to overcome this margin by consistently finding value.