{"source":"polymarket","id":"1079752","ticker":"spx-opens-up-or-down-on-september-28-2026","slug":"spx-opens-up-or-down-on-september-28-2026","title":"S&P 500 (SPX) Opens Up or Down on September 28?","description":"This market will resolve to \"Up\" if the official S&P 500 Index open price for S&P 500 (SPX) on September 28 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 September 28 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":"2026-09-25T12:01:00Z","end_date":"2026-09-28T20:00:00Z","closed_time":null,"volume":1633.2835759999998,"volume_24hr":1633.283576,"volume_24h_change":null,"normalized_vol_24hr":19.79094123840332,"normalized_volume":12.443954467773438,"liquidity":1422.2308,"open_interest":1420.782115,"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":0.075,"top_outcome_prob_24h_change":-0.365,"top_outcome_volume_24h_change":1633.283576,"updated_at":"2026-09-28T08:29:32.569013Z","fetched_at":"2026-09-28T08:29:32.569013Z","added_at":"2026-09-25T12:15:29.993048Z","url":"https://polymarket.com/event/spx-opens-up-or-down-on-september-28-2026","chart_24h":[0.0,0.0,0.0,0.0,0.0,0.0,20.0,20.0,20.0,60.0,60.0,252.888889,379.998889,584.998889,602.578889,602.578889,602.578889,602.578889,602.578889,622.578889,918.1644749999999,1018.164475,1100.127144,1196.127144,1371.964316,1421.964316,1633.283576],"kind":"live","markets":[{"source":"polymarket","id":"4947291","event_id":"1079752","slug":"spx-opens-up-or-down-on-september-28-2026","question":"S&P 500 (SPX) Opens Up or Down on September 28?","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 September 28 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 September 28 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":[0.075,0.925],"probability":0.075,"spread":0.05,"active":true,"closed":false,"start_date":"2026-09-25T12:01:00Z","end_date":"2026-09-28T20:00:00Z","closed_time":null,"volume":1633.2835759999998,"volume_24hr":1633.283576,"prob_24h_change":-0.365,"volume_24h_change":1633.283576,"normalized_vol_24hr":21.329975128173828,"normalized_volume":16.061626434326172,"liquidity":1301.6407,"categories":["Finance"],"countries":[],"updated_at":"2026-09-28T08:09:00.170727Z","fetched_at":"2026-09-28T08:09:00.170727Z","added_at":"2026-09-25T12:15:30.276855Z","url":"https://polymarket.com/event/spx-opens-up-or-down-on-september-28-2026/spx-opens-up-or-down-on-september-28-2026","event_title":"S&P 500 (SPX) Opens Up or Down on September 28?","chart_24h":[0.44,0.44,0.44,0.38,0.405,0.415,0.455,0.31,0.355,0.39,0.33,0.315,0.2,0.115,0.125,0.12,0.135,0.115,0.085,0.075]}],"_meta":{"attribution":"pdata.world — aggregated prediction-market data across 8 platforms","canonical_url":"https://pdata.world/events/polymarket/1079752","as_of":"2026-09-28T08:38:41.369687Z","docs":"https://api.pdata.world/docs","cite_as":"According to pdata.world (tracking Polymarket): \"S&P 500 (SPX) Opens Up or Down on September 28?\" — top market at 8% probability across 1 outcome","source_url":null}}