What is this market about?

S&P 500 (SPX) Opens Up or Down on April 21? The market resolves on Apr 21, 2026 based on the rules described on Polymarket.

How does intra-market arbitrage work here?

If the best-ask prices for every outcome sum to less than $1.00, you can buy each outcome and be guaranteed a $1.00 payout regardless of which one resolves YES.

Polymarket taker fees on this category are typically between 0% and 1.8%. Confirm the live fee on Polymarket before placing orders.

Polymarket market analysis

S&P 500 (SPX) Opens Up or Down on April 21?

No edge

Ends Apr 21, 2026

24h Volume

$199,245

Liquidity

$298,088

Outcomes

Summary

This market will resolve to "Up" if the official S&P 500 Index open price for S&P 500 (SPX) on April 21 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 April 21 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

Spread analysis

No intra-market edge right now (sum of best asks is at or above $1.00).

Polymarket taker fees vary by category between 0% and 1.8%. Always confirm before sizing.

Outcomes

Outcome	Best ask
Up	100.0%
Down	0.1%

Price history

Last 7 days

Open on Polymarket

Frequently asked questions

What is this market about?: S&P 500 (SPX) Opens Up or Down on April 21? The market resolves on Apr 21, 2026 based on the rules described on Polymarket.
How does intra-market arbitrage work here?: If the best-ask prices for every outcome sum to less than $1.00, you can buy each outcome and be guaranteed a $1.00 payout regardless of which one resolves YES.
What are the fees?: Polymarket taker fees on this category are typically between 0% and 1.8%. Confirm the live fee on Polymarket before placing orders.