How accurate are prediction markets?

In September 2026, 59% of the 34 highest-volume Polymarket markets resolved to the outcome that was priced above 50% a day before close, with a Brier score of 0.239.

What is a Brier score?

The average squared difference between the forecast probability and the outcome (1 if it happened, 0 if not). Lower is better; a constant 50% forecast scores 0.25.

Which markets are included?

Resolved Polymarket events with more than $50K of volume in the selected window, up to 40 per month, graded on the price one day and one week before close.

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Resolved markets

Prediction market scorecard: September 2026

For every high-volume market that resolved, we record what Polymarket priced the eventual outcome at one day and one week before close. This is the record, good and bad.

Updated 2026-11-06 02:19 UTC · Source: Polymarket · 18+

Last 30 days Nov 2026 Oct 2026 Sep 2026 Aug 2026 Jul 2026 Jun 2026

Favorites that won

59%

20 of 34 markets where the eventual result was priced above 50% a day before

Brier score (1 day out)

0.239

0 is perfect, 0.25 is a coin flip

Markets graded

highest-volume resolutions, September 2026

Resolved markets, September 2026

Market	Result	1 day before	7 days before	Volume
Fed Decision in September? resolved September 16, 2026	25 bps increase	88.5%	52.5%	$208.0M
Which party will gain most seats in Russian Parliamentary Election? resolved September 21, 2026	United Russia (ER)	81.5%	79.5%	$52.1M
What price will Bitcoin hit in August? resolved August 24, 2026	↑ 80,000	57.4%	0.5%	$28.4M
Eagles vs. Bears resolved September 29, 2026	Bears	34.5%	37.5%	$19.8M
Rams vs. Broncos resolved September 28, 2026	Broncos	45.5%	43.5%	$17.1M
Broncos vs. Chiefs resolved September 15, 2026	Chiefs	56.5%	56.5%	$16.0M
Colts vs. Chiefs resolved September 21, 2026	Chiefs	71.5%	71.0%	$15.5M
Falcons vs. Packers resolved September 25, 2026	Falcons	30.5%	26.5%	$14.5M
Norway vs. Denmark resolved September 24, 2026	Norway	55.5%	51.5%	$14.0M
Giants vs. Rams resolved September 22, 2026	Rams	73.5%	74.5%	$13.8M
Lions vs. Bills resolved September 18, 2026	Bills	67.5%	61.5%	$13.5M
Los Angeles Dodgers vs. Atlanta Braves resolved August 28, 2026	Atlanta Braves	49.5%	–	$12.1M
2026 Women’s US Open Winner (Tennis) resolved September 13, 2026	Elena Rybakina	42.7%	6.9%	$11.4M
What will WTI Crude Oil (WTI) hit in August 2026? resolved August 3, 2026	↓ $80	72.5%	58.5%	$11.4M
LoL: Hanwha Life Esports vs T1 (BO5) - LCK Playoffs resolved September 2, 2026	T1	43.0%	–	$11.0M
LoL: Gen.G vs Hanwha Life Esports (BO5) - LCK Playoffs resolved September 13, 2026	Hanwha Life Esports	–	–	$10.9M
LoL: Hanwha Life Esports vs T1 (BO5) - LCK Playoffs resolved September 12, 2026	Hanwha Life Esports	55.5%	–	$10.3M
LoL: Invictus Gaming vs JD Gaming (BO5) - LPL Regional Finals Playoffs resolved September 19, 2026	Invictus Gaming	–	–	$10.2M
LoL: Anyone's Legend vs Invictus Gaming (BO5) - LPL Playoffs resolved September 12, 2026	Invictus Gaming	51.5%	–	$10.2M
LoL: BNK FEARX vs Dplus KIA (BO5) - LCK Playoffs resolved September 3, 2026	BNK FEARX	35.0%	–	$10.1M
LoL: Top Esports vs Invictus Gaming (BO5) - LPL Regional Finals Playoffs resolved September 17, 2026	Invictus Gaming	53.5%	–	$10.0M
Real Betis Balompié vs. Getafe CF resolved September 17, 2026	Real Betis Balompié	58.5%	52.5%	$9.9M
Chiefs vs. Dolphins resolved September 27, 2026	Chiefs	84.5%	83.0%	$9.8M
Everton FC vs. Manchester United FC resolved September 6, 2026	Draw (Everton FC vs. Mancheste	26.5%	27.5%	$9.7M
LoL: T1 vs Dplus KIA (BO5) - LCK Playoffs resolved September 6, 2026	T1	53.0%	–	$8.8M
Counter-Strike: Spirit vs MOUZ (BO5) - BLAST Open Porto Playoffs resolved September 6, 2026	Spirit	–	–	$8.8M
LoL: KT Rolster vs Dplus KIA (BO5) - LCK Playoffs resolved September 4, 2026	KT Rolster	–	–	$8.7M
What price will Ethereum hit in August? resolved August 21, 2026	↑ 2,500	38.6%	0.8%	$8.6M
Brentford FC vs. Chelsea FC resolved September 18, 2026	Brentford FC	34.5%	33.5%	$8.6M
LoL: Bilibili Gaming vs Anyone's Legend (BO5) - LPL Playoffs resolved September 13, 2026	Anyone's Legend	–	–	$8.4M
Ravens vs. Cowboys resolved September 28, 2026	Ravens	61.5%	57.0%	$8.2M
LoL: Gen.G vs Hanwha Life Esports (BO5) - LCK Playoffs resolved September 5, 2026	Hanwha Life Esports	42.5%	–	$8.1M
LoL: Invictus Gaming vs Top Esports (BO5) - LPL Playoffs resolved September 5, 2026	Invictus Gaming	47.5%	–	$7.8M
Sporting CP vs. Galatasaray SK resolved September 9, 2026	Sporting CP	53.5%	50.0%	$7.3M
US Open ATP: Ben Shelton vs Carlos Alcaraz resolved September 9, 2026	Ben Shelton	21.5%	–	$7.3M
Chargers vs. Bills resolved September 27, 2026	Bills	75.5%	71.0%	$7.2M
LoL: Team WE vs JD Gaming (BO5) - LPL Regional Finals Playoffs resolved September 18, 2026	Team WE	45.0%	50.0%	$7.0M
US Open ATP: Frances Tiafoe vs Alex Michelsen resolved September 8, 2026	Frances Tiafoe	58.5%	–	$6.9M
LoL: Gen.G vs KT Rolster (BO5) - LCK Playoffs resolved September 1, 2026	Gen.G	69.5%	–	$6.9M

"1 day before" is the Polymarket price of the outcome that eventually happened, 24 hours before the market was closed for resolution. Brier score averages (1 - price)² over graded markets.

How to read the scorecard

Calibration, not hit rate, is the real test: a market is doing its job if outcomes priced at 70% happen about 70% of the time, which means favorites should lose roughly 30% of the time at that price. A Brier score near 0.1 across a month is strong; 0.25 is no better than a coin flip. Sample sizes here are small, so treat one month as a snapshot. Methodology and the full court and enforcement data live in the tracker and editorial standards.

Frequently asked questions

How accurate are prediction markets?: In September 2026, 59% of the 34 highest-volume Polymarket markets resolved to the outcome that was priced above 50% a day before close, with a Brier score of 0.239.
What is a Brier score?: The average squared difference between the forecast probability and the outcome (1 if it happened, 0 if not). Lower is better; a constant 50% forecast scores 0.25.
Which markets are included?: Resolved Polymarket events with more than $50K of volume in the selected window, up to 40 per month, graded on the price one day and one week before close.