What is a prediction market in simple terms?

A prediction market is a marketplace where people buy and sell contracts tied to the outcome of a real-world question. A contract typically pays a fixed amount if the event happens and nothing if it does not, so its trading price becomes a live estimate of how likely the event is.

How does a price become a probability?

If a contract pays $1 when an event resolves yes and it trades at 63 cents, the market is implying roughly a 63% chance. Read the price in cents as a percentage and you have the market-implied probability.

Are prediction markets accurate?

In liquid, well-defined markets they tend to be well-calibrated: across many events priced near 70%, close to 70% actually happen. Accuracy degrades in thin markets, ambiguous questions, or when a single large trader dominates.

Is a prediction market the same as gambling?

The mechanics rhyme, but the purpose differs. Unlike a casino game with a fixed house edge and a chance-driven result, a prediction market prices real-world events that skilled participants can forecast — and the price is useful information whether or not you ever trade.

Where does WillThisHappen get its probabilities?

WillThisHappen reads live prices from prediction markets such as Polymarket, translates them into plain-English probabilities, groups related questions, and tracks how each one moves over time.

What is a prediction market?

The one-sentence definition

A prediction market is a marketplace where people trade contracts tied to the outcome of a real-world question — an election, an interest-rate decision, a product launch — and the price at which those contracts change hands is a running, public estimate of how likely the outcome is. The price is not decoration; it is a forecast, updated continuously by people who lose money when they are wrong.

How a price maps to a probability

Most prediction-market contracts pay a fixed amount — usually one dollar — if an event resolves yes, and nothing if it resolves no. Because the payout is fixed, the price has a natural reading. A contract trading at 63 cents is the market saying the event has roughly a 63% chance. If you thought the true probability were much higher, 63 cents would look cheap and you would buy, nudging the price up; if you thought it lower, you would sell, pushing it down. The price settles where the marginal buyer and seller disagree, and that equilibrium is the market-implied probability.

Read the price of a “pays $1 on yes” contract in cents, and you can read it straight off as a percentage. 8 cents is about an 8% chance; 91 cents is about 91%.

As new information arrives — a poll, an earnings report, a resignation — the price moves within minutes, and so does the implied probability. That responsiveness is the whole point: a market is a forecast that never stops updating.

Why the number is usually well-behaved

Opinion polls ask people what they think. Prediction markets ask them to back it with capital, and being wrong has a cost. That single difference drives several forces that keep prices honest:

Skin in the game. Overconfidence is expensive; traders who are consistently wrong lose money and drop out.
Information aggregation. Thousands of participants each know a little, and the price folds all of it into one number.
Arbitrage. When a price drifts from what the evidence supports, someone can profit by correcting it.
Continuous updating. Markets react to news in real time, not on a polling cycle.

The result, in liquid and clearly-defined markets, is calibration: across a basket of events priced at 70%, close to 70% of them actually happen. That is a strong property, and it is why economists and journalists increasingly treat market prices as a serious signal alongside polls and models.

What people use them for

The practical value of a calibrated probability is that it replaces argument with a number you can act on:

Journalists and analystscite a live probability instead of hedging with “experts are divided”.
Businessesplan against the odds of a rate move, a regulatory decision or a rival’s launch.
AI agents and modelsground answers to “what are the odds of X” in a cited number rather than a hallucinated one.
Curious readers get a single, honest answer to a question that would otherwise dissolve into opinion.

The honest limits

A price is only as good as the market behind it, and it pays to know when to lean on one and when to hedge:

Thin markets are noisy. Low trading volume means a single large trade can swing the price further than reality justifies. Check liquidity before you trust a number.
Ambiguous questions resolve badly. If reasonable people can disagree about whether the event happened, the price is contaminated by resolution risk, not just the underlying odds.
Long-shots can be mispriced. Very unlikely events sometimes trade a little rich, a well-documented longshot bias.
A probability is not a promise. A 90% event still fails one time in ten — that is the forecast working, not failing.

None of this makes markets untrustworthy; it makes them a tool you read with judgement. A liquid market on a crisp question is one of the best forecasts you can find. A thin market on a vague one is a rumour with a percentage sign.

Where WillThisHappen fits in

Raw prediction-market prices are scattered, noisy and hard to read at a glance. WillThisHappen pulls the live feed, translates each price into a plain-English probability, groups related questions and tracks how every one moves over time — so you see not just where the odds sit but where they are heading. Browse the full set on the questions page, narrow by subject in the topics directory, or read the longer plain-English walkthrough in our guide.