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Placing your first trade on Polymarket

Find a market, read the book or AMM, understand Yes/No pricing and slippage, and see how cancellations and partial fills work.

·9 min read·Compliance reviewed

Polymarket

This guide walks through what placing a trade on Polymarket actually involves: finding a market, reading the order book (or AMM quote), picking Yes or No, sizing the order, setting slippage, confirming the order, and the two things that bite first-time traders most often — partial fills and cancels that didn't quite cancel.

It assumes you've already funded the current Polymarket collateral flow. If not, start with Getting started with Polymarket.

1. Find a market

Browse Polymarket's market list and evaluate two criteria:

  • Your probability estimate differs from the market. A trade with no estimated edge is a coin flip net of spread and fees. If you can't articulate why your probability differs from the market, treat that as a reason to keep researching rather than as a signal to trade.
  • The book is liquid enough for the hypothetical size. A $50 position on a thinly traded market is fine. A $5,000 position on the same market will fill at a much worse average price than the headline quote suggests. Check the book before increasing size. (See section 5 below.)

Read the resolution criteria carefully before placing the trade. Ambiguous wording is the source of most "I won but the market said no" complaints. A market about "by end of year" should specify a timezone; a market about "Company X" should specify the legal entity.

2. Read the book — or the AMM quote

Most actively traded Polymarket markets use a central limit order book: a list of resting bids and asks at specific prices.

Best bid is the highest someone will pay; best ask is the lowest someone will sell at. The gap is the spread.

A few things to read off the book before you trade:

  • Best bid / best ask. The two innermost prices — what you'd get buying or selling top-of-book.
  • Spread. Best ask minus best bid. On liquid markets this is often 1–2¢; on thin markets it can be 10¢+.
  • Depth. How much size sits at each level. The bigger your order, the more levels you'll walk into and the worse your average fill gets — see section 5.

Some markets — especially newer or low-volume ones — quote a single price from an automated market maker (AMM) instead of a book. The AMM holds inventory and quotes a price that moves continuously with the size of your order. Mechanically it's different from a book, but the practical question is the same: what price do I actually fill at for this size?

3. Pick Yes or No

Each market has two outcome tokens — usually YES and NO. Buying one is functionally the same as shorting the other:

  • Buy YES at $0.62 → you pay $0.62 per share now, get $1 if it resolves YES, $0 if it resolves NO.
  • Buy NO at $0.38 → mirror image. Pay $0.38, get $1 on NO, $0 on YES.

Since YES + NO ≈ $1 (modulo spread), the two are reflections of each other. In EV terms, the side whose price sits below your probability estimate has positive gross EV before fees and slippage. If your probability sits between the YES ask and the NO ask after accounting for spread, neither side has positive gross EV under that estimate.

See Expected value (EV) for the full walk-through of why this is the right frame.

4. Size the order

Two questions to answer before you type a number:

  • What's my edge? The difference between your probability and the market's price. A 5-cent edge is meaningfully different from a half-cent edge.
  • How much variance am I willing to take? EV doesn't tell you how often a single trade loses. A +EV trade can still lose; even a strongly +EV trade can lose multiple times in a row.

A common educational framework is fractional Kelly — modeling size as a small fraction (for example, 1/10 to 1/4) of full Kelly. Full Kelly maximises long-run growth under perfect assumptions but produces large drawdowns; fractional Kelly is often discussed as a way to model lower variance and probability-estimation error.

If "Kelly" is not useful yet, a small, consistent fraction of total funds per hypothetical trade is another way to study how probability estimates hold up in practice.

5. Set slippage

Slippage is the gap between the price you expect and the price you actually fill at. On a book it comes from walking into deeper levels; on an AMM it comes from the price impact of your size.

Top-of-book holds for the size sitting there; bigger orders walk into worse prices. Slippage tolerance defines the worst fill the order flow will accept.

Polymarket lets users set a slippage tolerance on market orders — a maximum acceptable difference between quoted and filled price. If the order would fill worse than that tolerance, it's rejected.

  • For tiny orders that fit inside top-of-book size: tolerance typically matters less than it does on thin or fast-moving markets.
  • For larger orders on thin markets: model the expected fill and compare the slippage to the edge implied by your own probability estimate.
  • For limit orders: slippage tolerance doesn't apply — you've already specified the worst price you'll accept (the limit price).

6. Confirm and sign

Polymarket runs on Polygon, but the user-facing flow can involve signed orders, signed transactions, and relayed gas-sponsored transactions depending on the current product surface. Two common flavours:

  • Limit order. Posted to Polymarket's CLOB. It rests in the book until matched or cancelled. The first time you place an order, you may sign an approval for the relevant collateral or outcome-token contract.
  • Market order. Submits an order at the best available price up to your slippage tolerance. The same approval/signature concepts apply.

A confirmation window pops up in your wallet. Read it. Make sure the contract address and token amounts match the order you intended to place. Phishing campaigns sometimes mimic the Polymarket UI but ask you to sign approvals for unrelated contracts; the wallet confirm is the last line of defence.

After signing, the order or transaction enters the relevant Polymarket flow. Supported relayer flows may sponsor gas; direct on-chain interactions may still require POL/MATIC. The position appears once the platform and chain state have processed the fill.

7. Cancelling

Limit orders that haven't filled yet can be cancelled from the Polymarket order page. Cancellation may require a signed message or transaction depending on the current flow. A few things to know:

  • Cancels are not instantaneous. There's a short window between clicking Cancel and the cancel becoming effective. If a matching order arrives in that window, you can still get filled.
  • Cancels don't refund spread. The price you set on the limit order was your decision; cancelling just stops it from filling further.
  • Multiple cancels can stack operational costs. Polymarket may batch or sponsor some operations under the hood, but unsupported direct wallet actions can still involve network gas.

8. Partial fills

Limit orders can fill partially — you get some shares at your limit price and the rest stays open. This is the most common "surprise" first-time traders run into.

What happens with a partial fill:

  • The filled portion is yours. Those shares are in your wallet; P&L is computed normally.
  • The unfilled portion stays resting until matched or cancelled. Your effective cost basis is the average of the filled and any later fills — Polymarket shows the average inline.
  • You can cancel the rest. If the market has moved away from your limit price and you don't think the rest will fill, cancel the residual. Otherwise it sits at the original price waiting.

What appears in EdgeLedger

Once a fill is reflected in on-chain position data, EdgeLedger pulls it into your dashboard automatically:

  • Open positions — outcome token balance with current mark-to-market.
  • Trade history — once the market resolves, the entry shows realized P&L and ROI.
  • Watchlist — the market itself is one click away from being added to your watchlist for price alerts.

EdgeLedger reads the wallet you've connected; it doesn't talk to Polymarket's order endpoints directly. Fills (including partial fills) reflect in the open-positions view as the on-chain transfer confirms. Cancels remove an open order but don't change your on-chain token balances, so they don't alter what EdgeLedger shows in your positions.

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