Implied probability: turning betting odds into a percentage

Odds are probabilities in disguise. Converting a line into its implied probability is the most useful habit in reading a market.

The formulas

Minus (favorite): odds ÷ (odds + 100). −160 → 160 ÷ 260 = 62%.

Plus (underdog): 100 ÷ (odds + 100). +135 → 100 ÷ 235 = 43%.

Not 100%

62% + 43% = 105%. The extra 5% is the sportsbook’s margin — the vig — and why beating the market long-term is hard.

Why convert?

It turns a feeling into a testable number. If you think a dog wins 50% but the line implies 43%, the market may underrate them. That gap is the heart of “value.”

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