Market Expiry

When a prediction market is created, the contract specifies an expiry timestamp after which the Order Book closes and no further trades are matched. On Kalshi, this is called the market close date, and the markets team begins monitoring the Resolution Source from that point forward to determine the outcome. On Polymarket, the expiry date marks when the market is eligible for resolution proposals to the Oracle. The gap between expiry and actual Settlement can range from hours to days, depending on when the resolution source publishes official data. Traders who hold positions at expiry cannot exit through normal trading, so monitoring expiry dates is important for managing Liquidity Risk in a portfolio.

Expiry timing creates strategic implications for active traders. A market with a very tight expiry window, set to close just hours after an event, leaves little room for Resolution Criteria data to be confirmed, which can increase the chance of a delayed or ambiguous resolution. Conversely, markets with distant expiry dates may trade at depressed prices due to the time value of capital tied up in Position collateral. Experienced traders account for expiry when assessing Expected Value: a correct prediction on a long-dated market yields a lower annualized return than the same edge on a near-term market. Expiry also determines the last moment at which Arbitrage opportunities between correlated markets can be exploited before both settle.