Extended-hours trading (pre-market and after-hours)
Trading that takes place before and after the US regular session — the hours when the market reacts first to earnings and news.
No set formula — trading before the regular session = pre-market, trading after the regular session = after-hours (extended hours).
A large move up or down in extended hours means the market's first reaction to the earnings or news is strong.
In plain terms
The US stock market has fixed regular trading hours. Before they start (pre-market) and after they end (after-hours), you can still buy and sell on a limited basis — this is called extended-hours trading.
Most earnings releases come out right after the regular session closes (after-hours). That is why "earnings came out and the stock is already down 10%" often happens in extended hours.
What it tells you
It shows how the market first reacts to earnings and news. It is a window for gauging the mood before the regular session opens.
For investors in other time zones, this is the stretch that happens while they sleep, so checking extended-hours moves in the morning tells you what went on overnight.
Formula
No set formula — trading before the regular session = pre-market, trading after the regular session = after-hours (extended hours). (US regular session in local terms: 9:30 a.m.–4:00 p.m. ET; pre-market and after-hours sit on either side)
What high or low means
A large move up or down in extended hours means the market's first reaction to the earnings or news is strong.
That said, extended-hours moves often do not carry through to the next regular session. It is only a first reaction, not a final conclusion.
Extended-hours trading has few participants, so volume is thin. A small amount of shares can swing the price sharply, and moves can look exaggerated compared with the regular session.
It is harder to get filled at the price you want (spreads are wide), and extended-hours moves are sometimes reversed once the regular session opens.
A sharp extended-hours move is a first reaction, not a settled trend. Because volume is thin, the direction can differ in the next day's regular session.
Metrics to read alongside
See it in real stocks
Search US stocks on Stocklore to see SEC-filing-based financial metrics alongside the sector benchmark.
This explanation is for information and reference only and is not a recommendation to buy or sell any security. Investment decisions and their consequences are your own.