Learn the stock market › Volume and volatility › Lesson 5 of 5
Do gaps always fill?
How a gap happens
The price stands still while the market is closed, but news keeps coming: an earnings report before the open, something that happened overnight or a big move on other markets. The opening price is set in an auction where buyers and sellers meet, described in Pre-market trading and the opening auction. If it lands far from the previous close, there is a gap. Dividends and splits also move the price overnight, but they are not gaps and are taken out here.
Since 2010 the 20 companies have opened at least 2% from the previous close 5,739 times, about once every 14 trading days for each company.
Does the gap fill?
| Gap | Same day | Within a week | Within a month |
|---|---|---|---|
| Up 2–5% (2,497) | 29% | 62% | 76% |
| Up 5% or more (496) | 9% | 31% | 46% |
| Down 2–5% (2,243) | 29% | 67% | 83% |
| Down 5% or more (430) | 11% | 38% | 58% |
Small gaps filled more often than large ones. Of the 2–5% gaps up, 29% filled the same day, 62% within a week and 76% within a month. Of the gaps up of 5% or more, 54% were still open after a month, and of the gaps down of 5% or more, 42%. A big gap often comes from big news, and then the price has no need to go back.
So the saying that gaps always fill is not true. Many fill in the end, but nobody knows in advance when, and some never do.
Does the day carry on the same way?
After a gap, the price closed in the direction of the gap, above the open after a gap up and below it after a gap down, on between 48% and 51% of the days.
That is about the same as a coin toss. The gap alone doesn't say how the rest of the day goes.
An example
On Sep 24, 2026, Oracle opened 5.0% lower than the close the day before.
The gap filled 7 trading days later.
Test yourself
A stock opens 6% higher after an earnings report. What does history say about the gap?
More figures are on the page for Oracle.