S&P 500 (SPX) Opens Up or Down on August 31? Odds & Prediction Markets

Name: S&P 500 (SPX) Opens Up or Down on August 31?
Start: 2026-08-28T12:01:04.000Z
End: 2026-08-31T20:00:00.000Z

Description

This market will resolve to "Up" if the official S&P 500 Index open price for S&P 500 (SPX) on August 31 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 August 31 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 to Thursday, or the next most recent trading day. If the two prices are exactly equal, this market will resolve 50-50. Note that all figures will be rounded to the nearest cent using standard rounding. If SPX does not trade at all during the regular session, the market will resolve 50-50. If either of the relevant days are shortened (for example, due to a market holiday schedule), the official open/close price published by S&P 500 Index for that shortened session will still be used for resolution. If the previous trading day has no official closing price (for example, due to a trading halt into the market close, system issue, delisting, or other disruption), the market will use the last valid on-exchange trade price of the regular session as the effective closing price. The resolution source for this market is the Wall Street Journal, specifically the Open/Close values published by the WSJ under "Historical Prices". US: https://www.wsj.com/market-data/stocks EMEA: https://www.wsj.com/market-data/stocks/emea ASIA: https://www.wsj.com/market-data/stocks/asia

Polymarket

This market will resolve to "Up" if the official S&P 500 Index open price for S&P 500 (SPX) on August 31 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 August 31 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 to Thursday, or the next most recent trading day. If the two prices are exactly equal, this market will resolve 50-50. Note that all figures will be rounded to the nearest cent using standard rounding. If SPX does not trade at all during the regular session, the market will resolve 50-50. If either of the relevant days are shortened (for example, due to a market holiday schedule), the official open/close price published by S&P 500 Index for that shortened session will still be used for resolution. If the previous trading day has no official closing price (for example, due to a trading halt into the market close, system issue, delisting, or other disruption), the market will use the last valid on-exchange trade price of the regular session as the effective closing price. The resolution source for this market is the Wall Street Journal, specifically the Open/Close values published by the WSJ under "Historical Prices". US: https://www.wsj.com/market-data/stocks EMEA: https://www.wsj.com/market-data/stocks/emea ASIA: https://www.wsj.com/market-data/stocks/asia

Frequently asked questions

The dashboard for the S&P 500 open direction market on Polymarket tracks real-time odds and price movements for whether the S&P 500 will open higher or lower on August 31, 2026. It shows current probabilities, historical price trends, and 24-hour volume of $8,329 to help users monitor market sentiment and liquidity. This focused view lets participants see how trader expectations shift in the days leading up to the resolution date.

On Polymarket, the current odds reflect trader collective views, which can diverge from traditional analyst forecasts. Where analysts may emphasize macro indicators or earnings reports, market prices incorporate all publicly available information and real-time sentiment. This difference often creates opportunities when market probabilities shift sharply based on news or unexpected economic data releases close to the resolution date.

This market resolves around Aug 31, 2026, with the outcome confirmed once the opening level of the S&P 500 on that day is verifiable from credible public reporting. The result is determined by the official open price, comparing it to the previous day’s close to decide whether the market settles "Up" or "Down".

Key signals include major economic data releases such as U.S. jobs figures, inflation reports, or Federal Reserve policy updates, all of which can shift expectations for the August 31 open. Geopolitical developments, significant corporate earnings surprises, or sudden market volatility events may also cause rapid price swings in this market as traders reassess probabilities in the final days before resolution.

S&P 500 (SPX) Opens Up or Down on August 31?

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