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SPY: average overnight repricing vs average regular-session move, monthly

Answered against 22 years of US equities and 12 years of US options data and published with the query that produced it. This result is stored as of 2026-08-01, from AI Daily Market Research Reports: What Breaks.

as of series 24×3read in context →
SPY: average overnight repricing vs average regular-session move, monthly — 24 rows by 3 columns, computed from US exchange, SIP and OPRA data.
monthovernight_move_pctsession_move_pct
2024-080.6180.634
2024-090.3340.443
2024-100.3010.423
2024-110.3260.368
2024-120.3160.53
2025-010.5460.536
2025-020.3180.667
2025-030.570.876
2025-041.3051.898
2025-050.70.415
2025-060.320.414
2025-070.2260.325
2025-080.2550.442
2025-090.2630.304
2025-100.3820.512
2025-110.4760.686
2025-120.2370.384
2026-010.3360.324
2026-020.3130.672
2026-030.7240.725
2026-040.450.466
2026-050.3160.338
2026-060.5130.619
2026-070.420.371
Rows × columns
24 × 3
Period covered
to
Computed
Completeness
No missing values
Source
US exchange, SIP and OPRA market data
Licence
Strasmore terms · free, no signup
Formats
JSON · CSV · the SQL below

What each column holds

Column definitions for SPY: average overnight repricing vs average regular-session move, monthly, derived from the stored result.
ColumnTypeRangeNotes
month date 2024-08 to 2026-07
overnight_move_pct number 0.226 to 1.305 percent
session_move_pct number 0.304 to 1.898 percent

Computed from Strasmore's warehouse of US exchange, SIP and OPRA market data. Equity prices are delayed; options greeks and implied volatility are end-of-day. This result is stored, not recomputed on load — it is exactly the numbers that were returned on , and the query below is what returned them.

the exact SQL behind every number
WITH bars AS (
    SELECT toDate(toTimeZone(window_start, 'America/New_York')) AS d,
           argMin(open, window_start) AS session_open,
           argMax(close, window_start) AS session_close
    FROM global_markets.delayed_stocks_minute_aggs
    WHERE ticker = 'SPY'
      AND toDate(toTimeZone(window_start, 'America/New_York')) >= toDate('2024-08-01')
      AND toDate(toTimeZone(window_start, 'America/New_York')) <= toDate('2026-07-31')
      AND (toHour(toTimeZone(window_start, 'America/New_York')) * 60
           + toMinute(toTimeZone(window_start, 'America/New_York'))) BETWEEN 570 AND 959
    GROUP BY d
),
linked AS (
    SELECT d,
           session_open,
           session_close,
           lagInFrame(session_close) OVER (ORDER BY d ASC ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) AS prior_close
    FROM bars
)
SELECT formatDateTime(toStartOfMonth(d), '%Y-%m') AS month,
       round(avg(abs(session_open / prior_close - 1)) * 100, 3) AS overnight_move_pct,
       round(avg(abs(session_close / session_open - 1)) * 100, 3) AS session_move_pct
FROM linked
WHERE prior_close > 0
GROUP BY month
ORDER BY month ASC

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