S&P 500 (SPX) Opens Up or Down on September 18?
What resolves this contract
This market will resolve to "Up" if the official S&P 500 Index open price for S&P 500 (SPX) on September 18 is higher than the official S&P 500 Index closing price for SPX on the most recent prior trading day. This market will resolve to "Down" if the official S&P 500 Index open price for S&P 500 (SPX) on September 18 is lower than the official S&P 500 Index closing price for SPX on the most recent prior trading day. E.g., ordinarily, a market on Monday would refer to the previous Friday for its most recent closing price, unless that Friday were a market holiday, in which case it would refer
How to read the price
Prediction market prices are expressed in cents on the dollar. A YES contract trading at 99¢ means the market is pricing in a 99.0% implied probability of the event resolving YES. If resolution comes back YES, the contract pays $1. If NO, it pays $0.
Volume vs. open interest
Total traded volume ($9,882) reflects every buy and sell across the life of this contract. Open interest ($35,468) is the dollar value of positions currently held by traders. Deep liquidity and wide open interest are the two signals that the quoted price is reliable.
Where to trade this market
This contract is listed on Polymarket. PicksByOdds does not accept deposits, execute trades, or offer brokerage. We publish the data; you decide what to do with it.
Markets in the same story
| Market | YES | Volume |
|---|---|---|
| Will the Doge-1 Lunar Mission launch by December 31, 2026? | 3¢ | $994,536 |
| Will Anthropic IPO by September 30, 2026? | 1¢ | $994,140 |
| Will Lovable be acquired before 2027? | 5¢ | $982,488 |
Common questions about this market
How is this market resolved?
This market will resolve to "Up" if the official S&P 500 Index open price for S&P 500 (SPX) on September 18 is higher than the official S&P 500 Index closing price for SPX on the most recent prior trading day. This market will resolve to "Down" if the official S&P 500 Index open price for S&P 500 (SPX) on September 18 is lower than the official S&P 500 Index closing price for SPX on the most recent prior trading day. E.g., ordinarily, a market on Monday would refer to the previous Friday for its most recent closing price, unless that Friday were a market holiday, in which case it would refer
When does this contract expire?
This contract closes on 2026-09-18. After close, the final outcome is determined per the resolution rules above, and contracts settle at $1 (winning side) or $0 (losing side).
What happens if I buy YES at 99¢?
If the event resolves YES, each YES contract pays $1, a profit of 1¢ per dollar risked. If it resolves NO, the contract pays $0 and the full 99¢ is lost. Current market price implies a 99.0% probability of YES.
Where is this market listed?
This contract is listed on Polymarket. PicksByOdds aggregates and displays public market data; we do not broker trades or custody funds.
How reliable is the quoted price?
This market has $9,882 in total traded volume and $35,468 in open interest. Deeper liquidity generally means tighter spreads and more reliable implied probabilities. Prices refresh multiple times per day.