Accumulator Probability
Each extra leg creates another condition that must succeed. Even individually plausible selections can produce a low-probability combined outcome.
Multiplying probabilities
If three independent events each had a true 50% chance, all three occurring would have a probability of 0.5 × 0.5 × 0.5 = 12.5%.
Real football outcomes are not always independent, and bookmaker prices include margin. Use this principle as an educational model, not a prediction engine.
Read bookmaker margin and value betting.