How Accurate Are Polymarket's Election Predictions? A Calibration Analysis

The question

"How accurate is Polymarket?" is the single most common question readers of this site ask. It is also a poorly-defined question. Accuracy against what metric — did the favorite win? Did the probability match the real-world frequency? Did the market beat polls?

This piece walks through each of those definitions and what the data actually says.

The 2024 headline

Polymarket's 2024 US presidential market had Donald Trump favored over Kamala Harris for most of the final two months of the campaign. By late October, Trump traded between 60% and 65% implied probability. Consensus polling aggregators at the same time showed a near 50/50 race. FiveThirtyEight had Harris slightly favored in their final forecast; Nate Silver's Silver Bulletin had Trump up a few points but closer to a coin flip than Polymarket implied.

On Election Night, Trump won the popular vote and all seven swing states. Polymarket's late-cycle pricing was closer to the outcome than the polling consensus.

This is the single data point most widely cited for "Polymarket called it better than polls." It is one race, with a specific dynamic (late-cycle GOP momentum that polls historically under-detect), and generalizing from a single high-profile race is the classic overfitting mistake. The more interesting question is whether markets are systematically better, not whether they nailed one cycle.

Calibration, not just hit rate

The right frame for evaluating a probabilistic forecaster is calibration: of all the events you priced at X%, did the event actually happen X% of the time?

A well-calibrated forecaster priced a set of events at 70%; 70% of those events happened. A poorly-calibrated forecaster priced the same events at 70% but only 50% of them happened (overconfident), or 90% of them happened (underconfident).

Polymarket's liquid political markets have been studied by academic researchers, platform analysts, and third-party groups like Metaculus. The rough finding:

• Markets priced at 80–95% correctly resolve 80–95% of the time. (Well-calibrated at the high end.)
• Markets priced at 20–50% correctly resolve at rates within 3–5 points of the stated probability. (Small mid-range miscalibration, tending toward slight overconfidence on favorites.)
• Markets priced at 50–80% — the contested-race range — are where calibration is strongest and most useful.

This is similar to what researchers find for weather forecasters, expert pundits in aggregate, and the best polling-based probabilistic forecasts (538, Silver Bulletin). Polymarket is not a magical oracle — it is one well-calibrated source among several.

Where markets beat polls

Two structural reasons markets often beat polls at the margin:

Markets aggregate non-poll information. Traders have access to endorsements, filings, fundraising reports, judicial decisions, and insider signals that polls cannot measure. When a major endorsement happens at 2 PM, markets move that afternoon; polls capture it a week later if at all.

Markets price in late-cycle dynamics that polls systematically miss. Polling has historically under-measured late-swinging Republican support, particularly among low-propensity voters in the Trump era. Markets, which incorporate late-breaking signals and take positions from informed traders, capture this earlier.

Where polls beat markets

Markets are not always the right tool:

Markets can be manipulated in thin races. A state legislature race with $50,000 in total volume can be priced by a handful of traders with local knowledge — or a partisan with a thesis. Polls, even bad ones, require more signal to move.

Markets under-sample information cascades. When a piece of news breaks that markets interpret one way and it turns out to be false or misread, the market can overshoot. Polls, slower to react, sometimes end up closer to the truth by accident.

Markets have baseline costs. Trading fees, spreads, and capital lockup mean priced probabilities embed a small "house edge." The implied probability is slightly biased upward on favorites and downward on long shots (the favorite-longshot bias that sportsbooks exhibit). The effect is small — 1–3 points typically — but present.

What calibration actually looks like over many races

Published calibration curves for prediction markets and aggregators (Polymarket, Metaculus, PredictIt pre-shutdown, Good Judgment Open) all converge on a similar picture:

• Markets are directionally accurate — favorites win more often, probabilities track outcomes in the expected direction.
• Markets are within a few points of perfectly calibrated — usually good to within 3–5% across probability bins when measured over hundreds of resolved events.
• Markets are better on liquid contracts than illiquid ones — volume is a reasonable proxy for calibration quality.

A market priced at 75% that resolves YES is not "right" in any final sense. A 75% forecast is well-calibrated only if it resolves YES about 75% of the time across many such bets. Individual outcomes tell you nothing; the aggregate does.

What we track

Our calibration track record page logs every major market we cover on resolution. Over time it will support a published calibration curve for the specific slice of political markets this site writes about. We include misses, not just hits — a site that only reports its wins is selling a story, not doing calibration.

Practical takeaways

For a reader trying to decide whether to trust a Polymarket number:

1. Check the liquidity. A market with $5M+ in volume is likely well-priced. One with $50K is more of a suggestion.
2. Compare to polling aggregators. If Polymarket and FiveThirtyEight agree within a few points, confidence is high. If they diverge by 10+ points, something is either genuinely uncertain or one of them is wrong — and figuring out which is interesting in itself.
3. Account for the event's time horizon. A 70% market 18 months from the event is much less reliable than a 70% market one week out.
4. Read the resolution source. Some markets resolve on ambiguous criteria (e.g., "will X happen by Y date"). The pricing incorporates resolution risk; it is not pure event probability.

FAQ

Did Polymarket predict the 2024 election correctly? Yes, Polymarket's 2024 presidential market had Trump favored over Harris for most of the final two months, and Trump won. Polymarket's final pricing was closer to the outcome than most polling aggregators.

Are prediction markets more accurate than polls? Usually within the same few-point margin as the best polling aggregators. Markets react faster to news; polls are more stable. For liquid contracts, markets tend to have a small edge.

Can Polymarket be manipulated? In thin markets, yes — a single trader can move a quiet contract. In the highest-volume markets (presidential winner, party control), manipulation would cost more than any informational benefit, so it is rare.

How do I check if a Polymarket number is reliable? Cross-reference with Kalshi (if it lists the same contract), polling aggregators, and our methodology notes.