Polymarket records lower midterm forecast errors than Kalshi across both chambers

Polymarket’s pre-close midterm prices were slightly more accurate than Kalshi’s for both the House and Senate, according to RotoWire’s assessment, updated at 3:16 PM ET on November 4.

A narrow difference in forecast accuracy

RotoWire assigned Polymarket a House Brier score of 0.0030, compared with 0.0045 for Kalshi. For the Senate, Polymarket scored 0.0600 against Kalshi’s 0.0625.

The pre-close prices put Democrats’ House probability at 94.5 percent on Polymarket and 93.3 percent on Kalshi. In the Senate market, Polymarket priced Democrats at 75.5 percent, while Kalshi stood at 75.0 percent, according to RotoWire.

Election-night prices converged

Both platforms moved above 99 percent by about 10 PM ET on election night, RotoWire reported. The accuracy comparison therefore concerns the pre-close prices, rather than those later readings.

The findings were summarized in material published on Nov 4, 2026, at 4:15 PM ET. They give Polymarket a modest advantage in this comparison, with both platforms assigning similar probabilities to Democrats in each chamber.

What it means for prediction markets

• Timing matters: RotoWire graded pre-close prices; the subsequent move above 99 percent represents a different forecast snapshot.
• The gap was small: Polymarket posted slightly better scores for both chambers, alongside slightly higher pre-close Democratic probabilities.
• The scope is limited: This assessment compares the two platforms’ House and Senate forecasts, not their performance across other markets.