Odds and Probability Calculator
Moves between the two common ways of expressing a chance.
Probability
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Odds in favour —
Odds against —
Decimal form (1 ÷ probability) —
Reading this —
The formula
probability = a ÷ (a + b), for odds of a to b odds in favour = p ÷ (1 − p)
These are true odds, without any built-in margin.
What to watch out for
A quoted price in a market or a betting shop includes the seller’s margin, so its implied probabilities add up to more than 100% and are not the true chance.
Frequently Asked Questions
What are odds of 3 to 1 as a probability?
75% if in favour, 25% if against.
What is a 20% chance as odds?
0.25 to 1 in favour, or 4 to 1 against.