Share of sessions where the rest of the day went the same way as the window
- First 30 minutes (9:30 to 10:00 am)
- Base rates: an unrelated session, a later 30-minute window
Hover or tap a column.
November 3, 2026 · 4 min read
Does the First 30 Minutes Set the Direction of the Day? ES and NQ Against Their Base Rates
The rest of the session went the same way as the first 30 minutes on 51.9% of NQ sessions since 2013 and 51.0% of ES sessions since 2011, against 50.3% and 50.1% when one session's open is paired with another session's rest of day. Only large opening moves show a tilt, and mostly since 2019.
A common piece of trading lore says the first 30 minutes of the session set the tone: if the market is up at 10:00 am, it tends to stay up into the close. The claim is usually quoted against a coin flip. The better question is whether the opening half hour says more about the rest of the day than any other half hour does, and more than an unrelated day's opening would.
The base rate
We split every full regular session of ES and NQ at 10:00 am and asked whether the change from 10:00 am to the close had the same sign as the change from 9:30 to 10:00 am. Index futures rise a little more often than they fall in both halves, so two unrelated half-days agree slightly more than half the time. To measure that, we paired each session's first 30 minutes with the rest of a session at least 26 sessions away, over every such offset. That pairing is the base rate.
| Market | Window | Sessions | Same direction | 95% interval |
|---|---|---|---|---|
| ES | First 30 minutes | 3,837 | 1,955 (51.0%) | 49–53% |
| ES | Unrelated session (base rate) | 3,837 | 50.1% | – |
| ES | Later 30-minute windows | 33,012 windows | 16,752 (50.7%) | – |
| NQ | First 30 minutes | 3,413 | 1,770 (51.9%) | 50–54% |
| NQ | Unrelated session (base rate) | 3,413 | 50.3% | – |
| NQ | Later 30-minute windows | 30,309 windows | 15,359 (50.7%) | – |
On ES, the rest of the session followed the first 30 minutes 51.0% of the time, against 50.1% for an unrelated session. On NQ it was 51.9% against 50.3%. Both are close to a coin flip. When we slid the opening half hours along the calendar, 29% of the 3,785 shifted versions on ES and 7.5% of the 3,361 on NQ matched the real gap or beat it. ES shows nothing. NQ shows a hint that does not clear the usual bar.
Is the opening half hour special?
The lore is about the open, so the fair comparison is with the half hours that follow it. We took each half hour starting from 10:00 am to 2:00 pm, nine windows a day, and asked the same question of the rest of its session. Pooled, those later windows agreed with the rest of the day 50.7% of the time on both markets. The opening window beat them by 0.4 points on ES (block-bootstrap interval −1.1 to +1.9 points) and by 1.2 points on NQ (−0.4 to +3.0 points). Both intervals include zero.
Every 30-minute window against the rest of its session, with 95% intervals (top: ES, bottom: NQ)
- Opening window
- Later windows
- 50%
Hover or tap a row.
Large opening moves
A second version of the claim says only a strong open counts. We marked a first 30 minutes as large when its move was bigger than the 75th percentile of the previous 250 sessions' opening moves, which is known at 10:00 am. On those sessions the rest of the day went the same way 53.7% of the time on ES (873 sessions, interval 50–57%) and 55.2% on NQ (829 sessions, 52–59%), against 50.2% and 50.1% for unrelated pairings: 3.5 and 5.2 points above the base rate.
| Market | Era | Sessions | Same direction | 95% interval |
|---|---|---|---|---|
| ES | 2011–2018 | 394 | 207 (52.5%) | 48–57% |
| ES | 2019–2026 | 479 | 262 (54.7%) | 50–59% |
| NQ | 2013–2018 | 324 | 170 (52.5%) | 47–58% |
| NQ | 2019–2026 | 505 | 288 (57.0%) | 53–61% |
On NQ, 0.3% of shifted versions matched the large-open gap, so it survives being the best of four looks. On ES, 3.7% did, which does not. The sign holds in both eras on both markets, but the earlier eras' intervals reach below 50%, and most of the effect sits in 2019–2026. Across every NQ session the rest of the day averaged +0.046% after an up first 30 minutes and −0.009% after a down one: a tilt in how often, not a large difference in how far.
What it does and does not say
For an ordinary session, the direction of the first 30 minutes says little about the rest of the day, and no more than a half hour taken later in the session. After a large opening move there is a modest tendency for the day to continue, clearest on NQ and in recent years. A rate of 55% is still a loss on nearly half of the sessions, and this post measures direction, not size, costs or a hypothetical trade.
- Base rate: compare with an unrelated session's open and with later windows of the same day, not only with 50%.
- Condition: "the open sets the tone" and "a big open sets the tone" are different claims with different samples. Ask which one the stat measures.
- Era: the large-open tilt is stronger since 2019. Check whether the next version of the stat holds in both halves of its sample.
Data and method. E-mini S&P 500 (ES) and E-mini Nasdaq-100 (NQ) futures, regular-session 1-minute bars (9:30 am to 4:00 pm ET), ES from 3 January 2011 and NQ from 2 January 2013, both to 26 October 2026, the last session on file. Only full sessions count: early-close days, sessions with a contract roll inside them and sessions missing more than a few minutes are left out, as are sessions where either half was exactly flat. The first 30 minutes run from the 9:30 am open to the close of the 9:59 bar; the rest of the session runs from there to the 4:00 pm close. A later window is any half hour starting 10:00 am to 2:00 pm, measured from the previous minute's close, against the rest of its own session. The unrelated-session base rate pairs each session's first 30 minutes with the rest of the session at least 26 sessions away, over every such offset; the same shift gives the p values. A large opening move is one bigger than the 75th percentile of the previous 250 sessions' first-30-minute moves, known at 10:00 am. The opening-minus-later interval is a moving-block bootstrap with blocks of 20 sessions. Rate intervals are 95% Wilson intervals. Two markets and two conditions (every session, large openings only) make four looks on the opening window.