Here σ (sigma) is the expected move in index points, converted from option-implied volatility. ±1σ is one expected-move unit either side and ±1.5σ is wider. They are not fixed support or resistance, and price is not guaranteed to stay inside.
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Today's expected range (sigma band)
Prior S&P 500 index (SPX) close × (prior close of VIX1D, the 1-day expected volatility index, ÷ 100) ÷ √252. Today's range is fixed after the prior close and is not reset intraday.
Next trading day's expected range (intraday estimate)
Latest SPX × (latest VIX1D ÷ 100) ÷ √252. It moves with the data intraday and is used after the close to preview the next trading day. Latest values may come from delayed quotes.
Did past closes land inside the expected range?
Last 20 trading days
Date
Close
VIX1D
+1σ
−1σ
Inside ±1σ
Touched +1σ
Touched −1σ
Last 60 days: each close in sigma multiples
“Inside” means the close finished between −1σ and +1σ; “touched” means the day's high or low reached that bound — two different measures. Under an ideal normal distribution ±1 standard deviation covers about 68% of outcomes; these bands are estimated from option-implied volatility, so use the sample on this page for actual rates, not as a future probability or a strategy win rate. The page tries to refresh every 3 minutes; freshness follows the source timestamp, and history comes from daily records.
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