How far in advance are prediction markets right?

The decay curve

Reading the table: a Brier score is the mean squared error between the predicted probability and the outcome (0.25 is what always guessing 50% scores; 0 is perfect). Directional accuracy is how often the >50% side won. Coin-flip prices within ±2pts of 50% are excluded from grading — they make no call to grade.

What this means

The pattern is consistent: prices at resolution look near-oracular, a day out they are good but clearly imperfect, and the further back you go the closer they drift toward an informed guess. That decay is the honest answer to “do prediction markets work?” — they aggregate information impressively fast near the event, and the premium for reading them early is real but bounded.

It is also why ProbCast grades venues at a fixed 24-hour lead time on the accuracy leaderboard instead of at resolution: any venue can look perfect at settlement; foresight is what differentiates them.

Caveats, honestly stated

• Samples shrink as lead time grows: a market must have existed (and been tracked) N days before resolving to be graded at horizon N, so long-horizon rows are smaller and noisier.
• The sample skews toward short-dated markets (Kalshi's daily and weekly series resolve constantly), so composition differs across horizons — this is a living measurement, not a controlled experiment.
• The sample currently clears ProbCast's credibility gate (size, prediction spread, both outcomes observed). Numbers on this page move as new outcomes settle; that is the point.