The available documentation explains how Polymarket market making works, but it does not verify a particular author’s implementation or trading results. So this is a practical, evidence-based guide—not a first-person account or a claim of proven returns. Its central principle is to manage open orders and filled outcome shares together: quote around an independently estimated fair value, then adjust how much exposure you are willing to add or reduce.
What inventory-balanced market making means
Polymarket is a peer-to-peer prediction market: users trade outcome shares, and supply and demand determine market prices. A share price between $0.00 and $1.00 can be read as a market-implied probability, not a guaranteed forecast. The displayed price may be the midpoint between the best bid and ask; it is not necessarily a price at which you can trade. A buyer pays an available ask, while a seller receives an available bid. Polymarket’s prices and order book guide explains these distinctions.
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Market makers place bids and asks around an estimate of fair value so other traders can trade in either direction. As Polymarket’s Market Making documentation puts it, “Market makers maintain bids and asks around their fair value so other traders can execute in either direction.” The platform leaves the market maker to decide whether midpoint is a useful fair-value estimate and how much risk to take.
Inventory is the exposure created by outcome shares you already hold. A filled buy adds shares; a filled sell reduces them. A live order matters too: if it fills, it can change your position. An inventory-aware approach therefore considers both settled fills and open orders before quoting again. It aims to avoid accumulating an unwanted position; it cannot ensure a profit or prevent a loss.
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Build the quoting loop around exposure
The following is a general framework inferred from Polymarket’s documented order mechanics, not a platform-prescribed formula or a verified author strategy. It deliberately avoids a fixed skew equation: the documentation does not prescribe one.
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Estimate fair value independently
Form an estimate of the outcome’s value using a method appropriate to the market. Then compare that estimate with executable bids and asks in the order book. Do not treat the displayed midpoint as an assured execution price.
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Set exposure and quote limits
Decide how many shares you are willing to hold, how much additional exposure a live order could create, and what loss you can tolerate. Choose quote prices and sizes that fit those limits and the visible market depth. Polymarket’s market-making guidance also says to validate market status, minimum price increment, and minimum order size before submitting quotes.
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Account for current and potential inventory
Track filled shares alongside the remaining size of every open order. Include partial fills: a partly filled order leaves a smaller live amount but has already changed your position. Consider reducing the size or competitiveness of a quote that would add to an already large position, or improving a quote that could reduce it. These are illustrative controls, not rules prescribed by Polymarket.
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Reassess and manage resting orders
Revisit quotes when your position changes, market depth shifts, or material news could change your estimate. Cancel or replace quotes that no longer fit your assumptions or limits. A stale order can execute after the market has moved; canceling it removes the remaining open amount, but cannot undo a fill that already occurred.
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Review executions, not just posted prices
Record what filled, at what price, and whether it increased or reduced exposure. A quote may not fill, may fill only in part, or may execute as the market moves. A visible spread is not guaranteed profit: assess results after applicable fees, rebates, and execution quality.
Choose orders with their trade-offs in mind
| Order type | What it does | Main trade-off |
|---|---|---|
| Limit | Sets a price at which the order can execute or better. It may rest in the book, fill partially, or be canceled. | Controls the acceptable price, but does not guarantee execution. |
| Market | Trades against available liquidity at the best available quotes. | Can execute promptly, but the execution price depends on available liquidity and may differ from the displayed midpoint. |
Polymarket’s order-placement guide describes these behaviors. Before trading size, inspect bids, asks, and depth: a quote visible at the top of the book does not show how much liquidity is available at other prices.
Include the market’s fee schedule in the calculation
Fees depend on market category and platform parameters, so check the specific market’s current terms rather than assuming one schedule applies everywhere. On the Polymarket Fees page accessed October 7, 2026, the listed taker fee rates were 0.07 for Crypto, 0.05 for Sports, 0.04 for Finance, and 0 for Geopolitics; listed maker fee rates were 0. The page also describes maker rebates for some categories. These are platform-published parameters from that date, not guaranteed permanent rates. See Polymarket’s fee documentation for current terms.
The same page gives the fee formula as fee = C × feeRate × p × (1 - p), where C is the number of shares traded, feeRate is the category parameter, and p is the share price. For a given fee rate, the dollar fee is highest around a 50% share price and symmetric around that point. Treat the formula and rates as the page’s October 7, 2026 snapshot; verify them again before trading.
When evaluating a strategy, account for taker fees when applicable, any maker rebate only when the current program rules confirm eligibility, and the actual execution prices. Do not assume an order will qualify as maker or earn a rebate simply because it began as a resting quote.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Understand the operational and outcome risks
Polymarket describes orders as signed and submitted to its central limit order book (CLOB); matched trades settle on Polygon. Its Trading Overview says the exchange can match authorized orders but cannot set users’ prices or execute trades they did not authorize. A strategy still needs order monitoring: check fills and cancel remaining open amounts when they no longer fit the plan.
- Execution risk: limit orders can remain unfilled or fill only partially; market orders depend on available liquidity.
- Adverse selection: a quote can fill just as the market moves against the price you used.
- Position risk: inventory limits constrain intended exposure but do not eliminate losses. A binary outcome can move sharply or resolve against an open position.
- Model risk: an estimated fair value can be wrong, and a midpoint is not proof of fair value.
- Fee and rule changes: category parameters and rebate terms may change, so recheck the market’s terms.
What a credible performance report would need
No backtest, win rate, or realized return for this particular strategy is established by the cited documentation. A performance claim would need reproducible records and a clear method, including:
- How fair value and quote prices and sizes were determined.
- How inventory was measured, including the treatment of open orders and partial fills.
- Position and loss limits, and how quickly stale quotes were canceled.
- Trades, fees, qualifying rebates, and execution prices over a stated period.
- How the analysis accounts for market depth, changing conditions, and adverse selection.
Without that evidence, the framework above is an explanation of how inventory-aware quoting can be organized—not proof that it earns positive returns or reduces risk in practice.
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