TOTAL VOLUME:
$54.4b
24H VOL:
$234,875,025
OPEN INTEREST:
$1,205,330,693
501,301
Markets across
13,585
events
MATCHED EVENTS:
1,825
PLATFORM COVERAGE:
4
Polymarket:
51%
VS.
Kalshi:
49%
S&P 500 (SPX) Up or Down on April 8?
Description
This market will resolve to "Up" if the official S&P 500 Index closing price for S&P 500 (SPX) on Wednesday, April 8, 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 Wednesday, April 8, 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
PredictionHero - Resolution Divergence Alerts (RDA)
Divergence Detected
Issue:
Polymarket and Kalshi use fundamentally incompatible resolution frameworks. Polymarket resolves based on directional price movement (Up/Down vs. prior trading day), while Kalshi resolves based on absolute index level thresholds (50 binary outcomes at 25-point intervals). These frameworks cannot produce equivalent outcomes for the same underlying event.Hero Tip:
Do not assume these markets will settle identically. On Polymarket, a 0.5% move up resolves YES; on Kalshi, only moves that cross specific threshold levels (5850, 5875, 5900, etc.) resolve YES. A SPX close of 5860 on April 8 would resolve YES on Polymarket if prior close was below 5860, but may resolve NO on Kalshi if the prior close was already above 5850. Arbitrage risk is extreme—verify the prior trading day close and Kalshi's exact threshold structure before trading.Critical Divergence Points:
- Polymarket: Outlier: Resolves based on directional comparison between April 8, 2026 closing price and the most recent prior trading day closing price. YES if April 8 close is higher, NO if lower, 50-50 if equal. Source is Wall Street Journal Historical Prices. Key quote: 'This market will resolve to Up if the official S&P 500 Index closing price for S&P 500 (SPX) on Wednesday, April 8, 2026 is higher than the official S&P 500 Index closing price for SPX on the most recent prior trading day.'
- Kalshi: Outlier: Resolves based on absolute index level on April 8, 2026 end-of-day. Contains 50 separate binary outcomes, each resolving YES if SPX closes above a specific threshold (5850, 5875, 5900, 5925, ... up to 7325). Each threshold is independent; multiple outcomes can resolve YES simultaneously. Key quote: 'If the end-of-day S&P 500 index value on April 08, 2026 is above 5849.9999, then the market resolves to Yes.'
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