Prediction market calculators
Three calculators for the arithmetic that comes up around a prediction market. They run in your browser, there is nothing to sign up for, and you are welcome to link to any of them.
The calculators
Implied probability calculator
What does this price mean as a percentage?
Converts between a market price in cents, implied probability, and American, decimal and fractional odds. Also strips a bookmaker's margin out of a two-way line, so you can see what the quote says once its cut is removed.
Open the implied probability calculator →Parlay calculator
What do these legs pay together, and what do they cost?
Prices a parlay from its legs and shows the two numbers most parlay calculators leave out: how the bookmaker's margin compounds with every leg added, and how far correlated legs can move the true chance away from the multiplied one.
Open the parlay calculator →Kelly criterion calculator
The market says 50¢ and I think 60% — how much do I put on it?
Turns a disagreement with a price into a position size, in dollars, at full, half and quarter Kelly. Says plainly when your own number does not beat the price, which is the answer more often than not.
Open the kelly criterion calculator →
And some numbers rather than a calculator
If you need a figure rather than an answer, the running count of the prediction market catalog reports how many markets are live on Polymarket and where the last day’s volume went, recounted every hour, with its method and a citation line.
To try any of this on a real price without staking anything, every market on Papermarkets trades with simulated money — browse what is open or read the paper trading guide first.