Myth Test #1
Does the gap always fill? We tested 2,320 Nasdaq gaps
“The gap always fills” is one of the most repeated rules in day trading. We measured how often it actually happens on the Nasdaq-100, and compared it with a fair baseline.
Short answer
No. In 2,320 Nasdaq-100 gaps from 2010 to 2020, 59.5% filled the same day, but a fake gap the same distance in the other direction was reached 55.2% of the time. That leaves an edge of about 4 percentage points, and most of the “fill” is simply price travelling a short distance. Gaps larger than 1% filled only about 1 in 4 times.
The claim
Social media treats the opening gap as a magnet: if the Nasdaq opens above or below yesterday’s close, price will come back and “fill” it. Traders fade the open on that belief.
How we tested it
We counted every regular-session gap of at least 0.05% and checked whether price returned to the prior close before the 4:00 PM ET close. The important part is the baseline: for each real gap we also drew a fake gap the same distance on the other side of the open, and checked how often price reached that. If gaps were magnets, real gaps would fill far more often than fake ones.
Results
| Sample | Result |
|---|---|
| Real gaps, Nasdaq-100, Jan 2010 – May 2020 (2,320 gaps) | 59.5% filled the same day |
| Fake gap, same distance the other way | 55.2% reached |
| Gaps larger than 1% | about 1 in 4 filled |
| Recent gaps, QQQ, Nov 2023 – Oct 2026 | 55% filled, but price ran the same distance away 69% of the time |
What it means
- Small gaps fill because they are small. Price wanders a few points in either direction most mornings, so a nearby level gets touched whether or not it is a gap.
- Big gaps tend to keep going. Only about a quarter of gaps over 1% filled the same day.
- The last three years flipped it. On QQQ since late 2023, continuation (69%) beat the fill (55%).
Verdict: not a magnet. Fading every gap is betting on a 4-point edge that mostly comes from distance, with the biggest losses coming on the big gap days that don’t come back.
Method and data
- 2010–2020: Oanda NAS100 1-minute CFD data, used as a proxy for Nasdaq-100 futures.
- 2023–2026: QQQ hourly data, November 2023 to October 2026.
- Regular session 9:30 AM – 4:00 PM ET; gaps of 0.05% or more.
- Historical study of price behaviour, not a trading signal and not a trading system.
Questions
What percentage of Nasdaq gaps fill the same day?
In our study of 2,320 Nasdaq-100 gaps from 2010 to 2020, 59.5% filled the same day. A fake gap the same distance in the other direction was reached 55.2% of the time, so the real edge is about 4 percentage points.
Do large gaps fill?
Less often. Gaps larger than 1% filled only about 1 in 4 times in our 2010–2020 sample.
Is fading the opening gap a good strategy?
Not on its own. Most of the fill rate is explained by distance, and in recent QQQ data price ran the same distance away from the close 69% of the time, more often than it filled.
Keep reading
Cite this: Trading Decisions Lab, “Myth Test #1: Does the gap always fill?” (Oct 24, 2026). https://www.tradingdecisionslab.com/research/does-the-gap-always-fill
Simulated backtest. Hypothetical or simulated performance results have certain limitations and do not represent actual trading; see the full disclaimer. Past results don’t guarantee future results. Educational only, not financial advice. Futures are leveraged and you can lose more than your deposit.