The trading day: sessions, auctions and why timing matters
· beginner
Automated material · TradeAlmanac editorial deskDraft prepared by a language model from our stored data; not reviewed by an editor.
A trading day is not uniform. It consists of periods with different price-formation mechanisms, and that affects how orders fill.
The opening auction
Before the main session opens, orders are collected and the opening price is set at the level that fills the greatest volume. There are no individual trades at that moment — there is one calculation.
That explains why an opening price can differ noticeably from the previous close: overnight news accumulated and is absorbed all at once.
The main session
Continuous trading: orders fill as they meet in the book. Most of the turnover falls in this period.
The closing auction
The same mechanism at the end of the day. The closing price it establishes is used to calculate indices and revalue portfolios — which makes it more consequential than any other price of the day.
The evening session
An additional trading period after the main one. Liquidity is usually thinner, spreads wider, and moves on small volume sharper.
Weekends and holidays
The trading calendar does not coincide with the calendar of business days, and on some days only a reduced set of instruments trades. For return calculations and period comparisons this matters: a missing trading day is not the same as a day without change.
Related: Trading modes: why one security has several prices.
Draft prepared by a language model from our stored data; not reviewed by an editor.
Model: claude-opus-5
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