{"source":"polymarket","id":"864703","ticker":"spx-opens-up-or-down-on-august-18-2026","slug":"spx-opens-up-or-down-on-august-18-2026","title":"S&P 500 (SPX) Opens Up or Down on August 18?","description":"This market will resolve to \"Up\" if the official S&P 500 Index open price for S&P 500 (SPX) on August 18 is higher than the official S&P 500 Index closing price for SPX on the most recent prior trading day.\n\nThis market will resolve to \"Down\" if the official S&P 500 Index open price for S&P 500 (SPX) on August 18 is lower than the official S&P 500 Index closing price for SPX on the most recent prior trading day.\n\nE.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.\n\nIf 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.\n\nIf SPX does not trade at all during the regular session, the market will resolve 50-50.\n\nIf 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.\n\nIf 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.\n\nThe resolution source for this market is the Wall Street Journal, specifically the Open/Close values published by the WSJ under \"Historical Prices\".\n\nUS: https://www.wsj.com/market-data/stocks\nEMEA: https://www.wsj.com/market-data/stocks/emea\nASIA: https://www.wsj.com/market-data/stocks/asia","image":"https://polymarket-upload.s3.us-east-2.amazonaws.com/s-and-p-500-1e40af6979.png","icon":"https://polymarket-upload.s3.us-east-2.amazonaws.com/s-and-p-500-1e40af6979.png","active":true,"closed":false,"start_date":"2026-08-17T12:00:16Z","end_date":"2026-08-18T20:00:00Z","closed_time":null,"volume":2870.441422,"volume_24hr":2870.441422,"volume_24h_change":null,"normalized_vol_24hr":25.39010238647461,"normalized_volume":14.066900253295898,"liquidity":1559.2143,"open_interest":2082.736856,"categories":["Finance"],"tags":[{"id":"102683","slug":"spx","label":"SPX"},{"id":"102127","slug":"up-or-down","label":"Up or Down"},{"id":"102281","slug":"daily","label":"Daily"},{"id":"102682","slug":"indicies","label":"Indicies"},{"id":"120","slug":"finance","label":"Finance"},{"id":"102169","slug":"hide-from-new","label":"Hide From New"}],"synthetic":false,"is_group":false,"group_key":null,"parent_event_id":null,"probability":null,"spread":null,"top_outcome":"","top_outcome_probability":0.135,"top_outcome_prob_24h_change":-0.44499999999999995,"top_outcome_volume_24h_change":2870.441422,"updated_at":"2026-08-18T07:21:00.780693Z","fetched_at":"2026-08-18T07:21:00.780693Z","added_at":"2026-08-17T12:14:31.730910Z","url":"https://polymarket.com/event/spx-opens-up-or-down-on-august-18-2026","chart_24h":[0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,0.0,30.0,30.0,647.370367,657.370367,1085.0552,1179.930119,1179.930119,1179.930119,1431.013451,1431.013451,1586.801327,1664.9094340000001,1719.014338,2199.104338,2288.02142,2302.04919],"markets":[{"source":"polymarket","id":"3664693","event_id":"864703","slug":"spx-opens-up-or-down-on-august-18-2026","question":"S&P 500 (SPX) Opens Up or Down on August 18?","group_item_title":null,"description":"This market will resolve to \"Up\" if the official S&P 500 Index open price for S&P 500 (SPX) on August 18 is higher than the official S&P 500 Index closing price for SPX on the most recent prior trading day.\n\nThis market will resolve to \"Down\" if the official S&P 500 Index open price for S&P 500 (SPX) on August 18 is lower than the official S&P 500 Index closing price for SPX on the most recent prior trading day.\n\nE.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.\n\nIf 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.\n\nIf SPX does not trade at all during the regular session, the market will resolve 50-50.\n\nIf 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.\n\nIf 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.\n\nThe resolution source for this market is the Wall Street Journal, specifically the Open/Close values published by the WSJ under \"Historical Prices\".\n\nUS: https://www.wsj.com/market-data/stocks\nEMEA: https://www.wsj.com/market-data/stocks/emea\nASIA: https://www.wsj.com/market-data/stocks/asia","image":"https://polymarket-upload.s3.us-east-2.amazonaws.com/s-and-p-500-1e40af6979.png","icon":"https://polymarket-upload.s3.us-east-2.amazonaws.com/s-and-p-500-1e40af6979.png","outcomes":["Up","Down"],"outcome_prices":[0.135,0.865],"probability":0.135,"spread":0.05,"active":true,"closed":false,"start_date":"2026-08-17T12:00:16Z","end_date":"2026-08-18T20:00:00Z","closed_time":null,"volume":2870.441422,"volume_24hr":2870.441422,"prob_24h_change":-0.44499999999999995,"volume_24h_change":2870.441422,"normalized_vol_24hr":29.777111053466797,"normalized_volume":18.601787567138672,"liquidity":1555.5949,"categories":["Finance"],"countries":[],"updated_at":"2026-08-18T07:24:38.623852Z","fetched_at":"2026-08-18T07:21:01.109978Z","added_at":"2026-08-17T12:14:31.775013Z","url":"https://polymarket.com/event/spx-opens-up-or-down-on-august-18-2026/spx-opens-up-or-down-on-august-18-2026","event_title":"S&P 500 (SPX) Opens Up or Down on August 18?","chart_24h":[0.58,0.61,0.58,0.58,0.58,0.58,0.58,0.535,0.51,0.435,0.665,0.5,0.54,0.61,0.57,0.545,0.6,0.3,0.235,0.22,0.16,0.09]}],"_meta":{"attribution":"pdata.world — aggregated prediction-market data across 8 platforms","canonical_url":"https://pdata.world/events/polymarket/864703","as_of":"2026-08-18T07:26:04.729492Z","docs":"https://api.pdata.world/docs","cite_as":"According to pdata.world (tracking Polymarket): \"S&P 500 (SPX) Opens Up or Down on August 18?\" — top market at 14% probability across 1 outcome","source_url":null}}