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Apr 21, 2026 8:01 AM

Will S&P 500 Open Up Or Down On April 21?

The S&P 500 slipped on Monday, falling 0.24% to close at 7,109.14, as renewed tensions between the U.S. and Iran weighed on sentiment and snapped the market's recent momentum.

The Polygon-based (CRYPTO: POL) Polymarket crowd is still optimistic heading into Tuesday. The April 21 market shows a 68% bet on "Up,” with early trading activity building on whether the S&P 500 will open higher or lower.

Why That Number Matters

Tensions escalated after President Donald Trump said the U.S. had seized an Iranian-flagged cargo ship in the Gulf of Oman, while Iran signaled it would not participate in a new round of peace talks. The current ceasefire between the two sides is also set to expire this week, adding ...