A market's prices can include a margin, so converted probabilities are not automatically calibrated predictions. Comparing selections requires the same market and price basis.
Converting a quote into a percentage
For decimal odds, divide one by the price and multiply by 100. Odds of 4.00 produce 25%; odds of 1.25 produce 80%. This is a conversion of a quoted price, not a measurement of how often the event will actually occur. A market can reflect incomplete information, commercial margin and different opinions.
Consider a fictional two-outcome event priced at 1.80 on both sides. Each side implies approximately 55.56%, giving 111.11% combined. Mutually exclusive exhaustive outcomes cannot have true probabilities totalling more than 100%. The excess shows why raw implied probabilities must not automatically be treated as a coherent forecast.
Removing margin is an assumption
A simple normalisation divides each implied probability by their total. In the symmetric example, this gives 50% for each side. For an asymmetric market, proportional normalisation is only one possible allocation of margin. It does not reveal the bookmaker's exact view or prove a selection is valuable.
Correlated events and combinations
Multiplying probabilities is valid for independent events, or when the correct conditional probabilities are used. Two bets affected by the same match outcome can be correlated. Multiplying their standalone implied probabilities can produce a misleading combination estimate. Keep price conversion, fair-probability estimation and a personal prediction separate; they are three different calculations with different evidence requirements.
In practice
Hypothetical decimal odds of 2.50 imply 1 ÷ 2.50 = 0.40, or 40%, before any margin adjustment. That calculation does not establish that the event's true chance is 40%.
What to check
State the odds format, conversion and margin treatment. Do not label a price-derived number as a verified real-world probability.