Probability Calculator
Aggregate odds from multiple prediction market sources. Compute weighted consensus probabilities, detect arbitrage opportunities, and strip vig to find fair values.
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Results
Weighted Consensus
60.3%
Source Breakdown
Source
Y + N
Overround
Fair Value
Flag
Polymarket
1.020
+2.0%
60.8%
Fair
Kalshi
1.020
+2.0%
56.9%
Fair
How it works
How does the weighted probability calculation work?
Each source's YES price is multiplied by its weight, then divided by the total weight. Higher-weighted sources have more influence on the consensus probability.
What is vig-adjusted fair value?
When YES + NO prices sum to more than 1.00, the excess is the vig (vigorish). Fair value removes the overround: Fair = YES / (YES + NO).
How is arbitrage detected?
Arbitrage exists when YES + NO prices sum to less than 1.00—you can buy both sides for a guaranteed profit. The calculator flags any source where this occurs.