Method

Sources

Polymarket and Kalshi publish their prices with no account or key. Probdesk reads them every 30 seconds: order book (best bid, best ask) of match-winner markets 7 days ahead. The bookmaker consensus is the median of their no-vig probabilities.

Matching

A game is matched only when both teams are recognised on each platform and the times agree. When in doubt it stays separate: an extra row beats a false gap.

Gap

Difference, in probability points, between the highest and lowest price of the same outcome (mid between bid and ask).

Best buy

For each outcome, the lowest ask, fees included (Kalshi: 7% × p × (1 − p); Polymarket sports: 5% × (1 − p)), compared with the fair price: the bookmaker consensus when available, otherwise the average of the other markets. The edge is the difference.

What Probdesk is not

Probdesk takes no bets, holds no funds and gives no investment advice. A gap can vanish before it is taken, and prediction markets are not available everywhere.