Trading prediction markets

Prices are probabilities

Because a share pays $1 or nothing, its price in cents reads as the market’s probability: a Yes trading at 62¢ is the market saying roughly 62%. It is an estimate made by traders, not a promise.

A buy button shows the price you would actually pay — the best ask — and a sell shows the best bid. The midpoint between them is what a chance column shows, and a button shows it, labelled mid, only when there is no live book.

The trade ticket

The ticket opens on Buy · Market. You buy by entering dollars (pUSD) and sell by entering shares, with quick amounts for both. A sell never sells more shares than you hold.

Before you sign, the ticket shows what you would get in each outcome, both fees separately, and the fees as a share of your stake. “Fees are included in the payoffs.” The order is signed on your device.

Order types

Market

A Market order is capped at the best ask when you buy, or the best bid when you sell. It takes whatever the book offers at that price, cancels the rest, and never reaches further into the book — there is no slippage allowance. If the book is not live, the ticket says depth is unknown.

Limit

A Limit order rests at your price. By default it lasts until you cancel it; you can instead choose 1 hour, End of day (your next local midnight), Market end when the market has an end date, or a time of your own. An end time must be at least about 2 minutes away: Polymarket needs 3 minutes’ notice and ends an order a minute early, so Polydict adds that time back and the order ends when you chose.

Turn on Maker only and the order only ever rests: “If it would fill at once, Polymarket rejects it instead.” It is off by default. Without it, a limit priced across the book shows fills now and pays the taker fee like a Market order.

Fill or kill

Fill or kill is signed at the worst price the book needs to fill your whole order. If the book cannot fill all of it, the order is not sent; if the book moves before it arrives, Polymarket cancels it whole and nothing is spent.

Fees

Two fees can apply to an order, and the ticket shows each on its own line, in dollars and as a percent of your stake.

• Polymarket’s fee, paid by takers: shares × rate × price × (1 − price). It is largest near 50¢ and shrinks toward 0¢ and $1, and an order that rests on the book pays none of it (the row reads $0.00 · resting). The rate is the market’s own; when a market does not publish one, the app uses Polymarket’s category rate and marks the row est. Some markets have no fee at all.
• Polydict’s fee, shown as Polydict fee · 0.5%: 0.5% of the order’s value, on what fills, whether the order rests or takes, including markets where Polymarket charges nothing.

Combos and perps price their fees differently: see Combos and Perps.

Receipts

After you place an order, a receipt stays on the ticket until you dismiss it. It says plainly what happened:

• Filled — what you bought or sold.
• Partly filled — “Only part of the order could fill at its price; the rest was cancelled, not left open.”
• Resting — “It sits on the book until someone takes it. Cancel it any time from your open orders.”
• Fill or kill cancelled — “Nothing filled, nothing spent. The order book moved before your order arrived, so Polymarket cancelled it whole. Check the price and place it again if you still want it.”
• Market order matched nothing — “Nothing filled, nothing spent. No order on the book matched your price when yours arrived, so Polymarket cancelled it. Check the price and place it again if you still want it.”
• Lost contact — “We lost contact before confirming this order. It may still have been placed — check your positions and open orders before trying again.”

An amount marked ≈ is an estimate. If an order looks like a repeat of one that may still be live, the app warns you first: “This places a second, separate order. If the earlier one also fills, you will hold both positions and have paid for both.”

Open orders and cancelling

Every resting order is under Portfolio › Orders, each with its own Cancel. On a market page, the Terminal view lists that market’s open orders and adds Cancel all, which asks before it cancels.

How markets resolve

Markets resolve by Polymarket’s rules, through UMA’s Optimistic Oracle: someone proposes the outcome, a challenge window follows, and a disputed outcome goes to a UMA vote, which can take days. Each market page shows its rules, its resolution source and its current status under About & resolution. Polydict does not resolve markets and cannot change an outcome.

Up or Down windows settle on a named price feed instead: Up or Down.

Collecting winnings

When a market resolves your way, the position moves to Portfolio › Ready to collect. Collect (or Collect all) redeems it into your balance, without gas. Nothing is collected automatically.

Positions that resolved the other way are listed plainly under Settled against you, with what was lost, until you clear them.