01How Prices Become Probabilities
A prediction market turns trading around a defined outcome into a continuously updated implied probability. Evidence, liquidity, and positioning can all change that price before the contract settles.
A binary market resolves a deadline-based question toYes or No. The correct share pays $1 while the incorrect share pays $0, which is why $0.63 maps directly to 63%.
Contract cents map directly to percentage points
A YES contract at $0.63 implies roughly a 63% chance. If YES resolves, the gross payout is $1 and profit is $0.37 per share; if NO resolves, the $0.63 purchase is lost.
YES and NO should total about $1
Exactly one side pays $1 at resolution, so the two prices tend to sum to that amount. If YES costs $0.63, NO should sit near $0.37; a meaningful combined discount can attract arbitrage until the imbalance closes.
The named resolution source determines the winner
The resolution source, contract wording, and deadline decide which shares redeem for $1. Ambiguous criteria, publication delays, and dispute procedures therefore belong in the price you are willing to pay.
Trades execute against either pooled or posted liquidity
An automated market maker trades against pooled reserves; an order book matches prices posted by buyers and sellers. A hybrid venue combines both sources of execution.
AMMs calculate every quote
An AMM prices against pooled reserves, and each order changes the balance used to produce the next quote.
Learn how AMM prices move →Order books display trader prices
An order book lists resting bids and asks, then executes when buyers and sellers accept compatible prices.
Read bids, asks, and depth →02How AMMs Price Liquidity
An automated market maker always quotes from a formula applied to pooled reserves. Each fill alters those reserves, so increasing order size generally drives the average purchase price farther away from the displayed starting quote.
A constant-product AMM preserves x × y = k
The YES reserve multiplied by the NO reserve stays constant. Ifx represents YES and y represents NO, every transaction must rebalance the pool without changing their product:
The value k does not change. Buying YES reduces its reserve, forcing the next YES quote higher as the pool restores the product.
The direct consequence is that scarcity moves the price. Buying YES reduces its available reserve, making the next YES share more expensive. The formula updates every quote automatically as demand changes.
Probability-focused market makers
Purpose-built market makers like the Logarithmic Market Scoring Rule (LMSR) refine this idea for probabilities. LMSR uses a liquidity parameter that caps the market maker’s maximum loss while guaranteeing you can always trade, even in a thin market — the trade-off AMMs are designed to make.
A larger order creates more slippage
Slippage measures the gap between the displayed quote and your average fill. Large orders consume more reserve and travel farther along the price curve, while deeper pools absorb the same order more easily.
| Order size | Quoted price | Avg. fill | Slippage |
|---|---|---|---|
| 100 shares | $0.500 | $0.501 | 0.2% |
| 1,000 shares | $0.500 | $0.512 | 2.4% |
| 10,000 shares | $0.500 | $0.575 | 15.0% |
These shallow-pool figures show the rule: slippage rises as order size becomes large relative to available depth.
Liquidity providers earn fees for carrying inventory risk
A liquidity provider supplies reserves and receives trading fees in return for absorbing rebalancing risk. A sharp move can leave the pool concentrated in the losing side, creating impermanent lossthat fee income must overcome.
03How Order Books Execute Trades
An order book executes when a buyer takes an ask or a seller takes a bid. Its price levels reveal the spread and the quantity available before a larger order must continue at a less favorable price.
The best bid and ask define the spread
The highest bid and lowest ask are the closest prices available to trade, and their difference is the spread. The most recent match is the last trade; orders queued behind the top level make up the market's visible depth.
Best bid $0.62 vs. best ask $0.64 → a $0.02 spread. A market order to buy crosses the spread and fills against the asks.
Makers post liquidity; takers consume it
Makers add depth by leaving limit orders on the book;takers accept available quotes for an immediate fill. Takers may cross the spread and multiple levels, while makers risk waiting without ever trading.
Where order books work well
Liquid books provide tight spreads and visible depth, letting patient traders control their limit price.
Where order books break down
Thin books can show wide spreads or no resting orders, so execution stalls until someone is willing to quote.
Execution certainty and price control trade off
An AMM guarantees a price at every moment but charges you slippage. An order book can offer razor-thin spreads — but only when other traders show up. Many prediction-market platforms run a hybrid: an order book for depth, with an AMM backstopping liquidity when the book runs dry.
04How to Reduce Downside
Reduce prediction-market downside by shrinking or offsetting the position before resolution. You can sell shares, purchase the opposite result, cap the initial stake, or spread risk across unrelated event drivers; each method exchanges some potential profit for a narrower range of losses.
1 · Selling early turns an unrealized gain into cash
An early sale locks the price difference and removes settlement exposure. Buying YES at $0.40 and selling it at $0.75 realizes $0.35 per share no matter how the contract ultimately resolves.
2 · The opposite outcome can cap event exposure
Buying the other side reduces dependence on one resolution and can lock profit when YES plus NO costs less than $1. That discount is arbitrage; without it, a smaller opposing position can still soften a reversal while leaving some upside intact.
Opposite-side hedge example
You hold 1,000 YES @ $0.40 (cost $400). YES now trades at $0.70, so NO trades near $0.30. Buying 1,000 NO @ $0.30 ($300) guarantees $1,000 back at resolution. Total outlay $700 → a locked $300 profit, whichever way it resolves.
3 · Define the maximum loss before entry
A risk budget caps the bankroll damage from one incorrect probability. The Kelly criterion scales a position to the estimated edge and payout, while fractional Kelly discounts that result for forecast error. A weak or uncertain edge should produce a correspondingly small stake.
4 · Diversify across drivers, not merely contracts
Diversification helps only when positions react to genuinely different causes. Several contracts linked to one election, court ruling, or data release can hide a concentrated bet; less-correlated exposures make one forecasting mistake less damaging.
Sell strength to capture the move and remove settlement exposure.
Use the other side to cap the cost of an incorrect call.
Keep each market small enough that the bankroll survives a loss.
Combine less-correlated positions so one event cannot dominate results.
Every hedge has a price
A hedge is insurance, not a magic trick. It costs something — you pay a premium in forgone upside. The skill is deciding when that certainty is worth more than the gamble, and sizing the hedge so the peace of mind is worth the price.
05Essential Market Terms
Prediction-market vocabulary explains how contracts encode probability, how orders receive fills, how outcomes resolve, and where financial risk moves.
Verify the rules, executable price, forecast advantage, and worst-case loss
Start with the official resolution source, estimate your average execution price, and compare that total cost with an independent probability. Keep the position small enough that an incorrect forecast causes only a planned bankroll loss.