Block Trades on Prediction Markets: How Big Hedges Get Done
How a large position gets traded at one negotiated price, and why the exchange typically does not take a side.
Published 2026-10-26 · Market & data intelligence · Educational, not advice.
A block trade is a large contract that two counterparties negotiate privately and then clear through the exchange. It lets a big hedge get done at one price instead of buying through every order on the book. The block price usually includes a premium for size. A large print often shows that someone needed to move risk. It is not necessarily a new forecast. The exchange typically does not take a side.
The problem a block trade solves
A prediction market is an exchange. Every contract has a buyer and a seller. The exchange matches them, typically charges a fee and does not hold the other side itself. The price you see is where the most recent buyer and seller agreed, and it keeps moving until the outcome is known.
That works well for small trades. It gets awkward when someone needs to move a lot of contracts at once.
Picture a company whose costs rise if a rate decision goes one way, or a fund exposed to an election result. Either might want a position large enough to offset that risk. On an open order book, an order that size has to fill every resting order at the best price, then the next price, then the next. Each level costs more than the last. By the time the order fills, the average price can be well away from the price quoted a minute earlier.
That gap is called price impact, or slippage. A block trade is the standard tool for limiting it.
What a block trade actually is
A block trade is a large trade that two counterparties negotiate privately and then report to the exchange, which clears it. The order never goes into the public book to fill at one price after another. Instead, the two sides agree on a quantity and a single price away from the screen, then submit the trade for the exchange to record.
The idea comes from futures and equity markets. There, block rules usually cover minimum size, how the price must relate to the current market and how quickly the trade must be reported. Where a prediction market venue offers something similar, its own rulebook sets the details, and those details differ from venue to venue. For specifics, read the rulebook, not a blog post.
One thing generally stays the same: the exchange typically does not take a side. A block is still a buyer and a seller agreeing to a contract with each other. It just skips the step where that agreement is found one small order at a time.
How a large hedge typically gets done
The mechanics vary by venue, but the steps are usually similar.
- Request for quote. The party who needs size asks one or more liquidity providers, often professional market makers, for a price on a stated quantity. Some platforms have a built-in request-for-quote tool. Elsewhere this happens through direct relationships.
- Negotiation. The market maker quotes a price based on the current market, plus extra to cover the risk of taking on a large, possibly one-sided position. Larger size generally means a price further from the screen.
- Agreement and submission. Both sides agree, and the trade goes to the exchange. The exchange checks it against its rules and clears it like any other contract.
- Reporting. The trade appears in the public record. Some markets require this right away. Others may allow a short delay.
Notice who is on the other side. It is typically not the exchange but someone paid to take on risk. That market maker will usually try to reduce its new position over time. It does this by trading smaller pieces on the open book or in related contracts.
Why the block price differs from the screen price
People are sometimes surprised that a block trades at a different price from the last trade on screen. Usually it should.
The screen price comes from small buyers and sellers. A block counterparty is asked to take on much more risk in one trade, with no chance to build the position gradually, and it charges for that. A block that buys YES may trade somewhat above the visible ask, and a block that sells may trade below the bid. The difference is the cost of getting a large size filled immediately.
The trade-off for the hedger is paying one known premium instead of a rising, unknown cost spread across many fills.
It is also why a single large trade, or print, is weak evidence on its own. A block reflects one party's need to move size, not necessarily a new consensus about the outcome. A hedger may have no view at all. They may simply be offsetting risk they hold somewhere else.
What blocks mean for everyone else
For the rest of the market, blocks matter in a few less obvious ways.
- The aftermath can move prices. When the market maker sells down its new position on the open book, that trading can push the visible price for a while after the block itself.
- Reporting delays change what you see. Where delayed reporting is allowed, the public record of trades can lag behind what has actually traded.
- Depth matters more than the last price. Depth is how many contracts are offered near the current price. A contract with a thin book can look more settled than it is. The size available near the price tells you how far a large order would move it.
This is the big difference from a sportsbook. A sportsbook sets its own price, holds the other side and can limit or refuse large bets as it chooses. On an exchange, a large position needs a willing counterparty at an agreed price. The price impact comes from the orders on the book, not from a house decision.
Liquidity is rarely spread evenly, so it helps to compare depth and price for the same outcome across venues.
The takeaway
A block trade is a large contract negotiated privately and then cleared on the exchange. It lets a big hedge get done at one price instead of buying through the whole book. The exchange typically does not take a side. The block price includes a premium for size. A large print shows that someone needed to trade, not necessarily what anyone expects to happen.
Next in The Line: how market makers quote prediction market contracts, and what the gap between the bid and the ask actually pays for.
Sources
This explainer quotes no live prices. These are the regulator and platform pages that define how event contracts work.
References for this topic
- CFTC: Prediction markets (Learn and Protect)cftc.gov
- Kalshi Help Centerhelp.kalshi.com
- Polymarket documentation: Polymarket 101docs.polymarket.com
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