How Do Event Contracts Work? A Small Yes/No Example

An event contract is a financial contract whose payout depends on a specified event. In a common Yes/No structure, you buy one side at a market price; if that side wins, it pays $1 per contract, and if it loses, it pays $0. Yes wins if the specified condition is met; No wins if it is not, subject to the contract’s rules. The payout is not your profit: subtract what you paid and any fees.

The CFTC’s event-contract explainer describes this fixed-payout structure, while noting that other designs can have multiple outcomes or partial payouts. The example below uses ordinary $1-or-$0 contracts, not those alternatives.

Start with what “Yes” actually means

A headline such as “Will it be hot tomorrow?” is not precise enough to evaluate. The contract’s rules need to identify the measurement, location, deadline and source that determines the outcome.

Consider this hypothetical market, not a live listing:

Will the maximum temperature at Station A exceed 90°F on November 1, 2026, according to Agency B’s final daily report?

Under that wording, exactly 90°F is not enough for Yes. A temperature above 90°F at a different station is not enough either. Before considering a price, check:

• The exact threshold, date and relevant time zone.
• The official data source and which report or revision counts.
• Who determines the result and when.
• What happens if data is missing, the event is canceled or the normal outcome cannot be determined.

Do not assume every exception produces a refund. Kalshi’s market FAQs, for example, describe some rule-specific nonstandard payouts. They also distinguish trading close time from determination time: an event appearing to finish does not necessarily mean settlement is immediate.

Read the price—and the executable quote

For a contract that pays $1 if Yes wins, a 60¢ Yes price is commonly interpreted as roughly a 60% market-implied probability. It reflects traders’ expectations, not a verified chance or a guarantee. Prices arise through trading between participants; Kalshi explains how opposing Yes and No orders can match.

A displayed price may not be the price available for your order. In an order book:

• Bid: what a buyer currently offers; relevant when you sell.
• Ask: what a seller currently requests; relevant when you buy.
• Spread: the difference between the best bid and ask.

Polymarket’s order-book documentation illustrates this distinction: an immediate buyer pays the ask and an immediate seller receives the bid. Available quantity matters too; a larger order may need to trade at several prices.

A checkable example: buy 10 Yes contracts

Assume the hypothetical temperature market has a 58¢ Yes bid and 60¢ Yes ask, with enough quantity for all 10 contracts. Assume a 20¢ total entry fee. These are invented teaching figures, not an operator’s fee schedule. All results below are before taxes and assume no other charges unless stated.

Your purchase costs:

10 × $0.60 + $0.20 = $6.20

Outcome under the rules	Settlement payout	Net result after entry fee
Yes wins	10 × $1 = $10	$10 − $6.20 = +$3.80
No wins	10 × $0 = $0	$0 − $6.20 = −$6.20

For this fully paid purchase, the maximum loss is the $6.20 spent. A correct prediction produces a $10 payout—not $10 of profit.

If you hold to ordinary binary settlement with no further fees, the break-even probability—the probability needed for a zero expected net result—is:

$6.20 ÷ $10 = 62%

That is a cost threshold, not a forecast. You still need an independent estimate of the event’s chance; see probability basics.

Selling early changes the calculation

You can try to sell before trading closes rather than wait for settlement. An exit requires a matching buyer; a limit order controls your acceptable price but may remain unfilled or fill only partly, as Polymarket’s order documentation explains.

Suppose you immediately sell all 10 contracts at the unchanged 58¢ bid and pay an assumed 20¢ exit fee:

Sale proceeds: 10 × $0.58 − $0.20 = $5.60 Net result: $5.60 − $6.20 = −$0.60

The loss is 20¢ from crossing the spread plus 40¢ in fees. Do not subtract the spread again—it is already reflected in the purchase and sale prices.

Before submitting an order, be able to state the resolution rule, executable price, total cost, maximum loss and possible exit constraints. The final pre-trade checklist puts those checks in one place. This is education, not a recommendation to trade; use only money you can afford to lose.