S&P 500 (SPX) Up or Down on August 18?
The event deadline has passed. This market is awaiting formal resolution, so the price shown is the last traded level, not a live forecast.
- Last probability before deadline
- 0.1%
- Event deadline
- August 18, 2026 at 4:00 PM ET
- Venue status
- open
- Resolution source
- wsj.com
ProbCast Reliability Summary
S&P 500 (SPX) Up or Down on August 18? The last traded Polymarket probability before the deadline was 0.1%. The event deadline has passed. This market is awaiting formal resolution, so the price shown is the last traded level, not a live forecast.
- Market data as of
- August 18, 2026 at 4:05 PM ET
- ProbCast assessment generated
- August 18, 2026 at 4:12 PM ET
- Source
- Polymarket
- Event deadline
- August 18, 2026 at 4:00 PM ET
- Market status
- Awaiting resolution
What this market actually measures
This market will resolve to "Up" if the official S&P 500 Index closing price for S&P 500 (SPX) on Tuesday, August 18, 2026 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 closing price for S&P 500 (SPX) on Tuesday, August 18, 2026 is lower than the official S&P 500 Index closing price for SPX on the …
This summary shows the opening of the venue's official rules. ProbCast has not yet generated an independent plain-English interpretation for this contract — review the full rules before relying on it.
View full official resolution rules
This market will resolve to "Up" if the official S&P 500 Index closing price for S&P 500 (SPX) on Tuesday, August 18, 2026 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 closing price for S&P 500 (SPX) on Tuesday, August 18, 2026 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 specified closing 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 closing price published by S&P 500 Index for that shortened session will still be used for resolution. If either of the relevant days have 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 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