Market Hours and Sessions: When Markets Trade, and Why It Matters

Meanwhile the currency market barely closes at all, running continuously from Monday morning in Asia to Friday evening in New York. This article maps the clock: what the sessions are, why the open and close are special, what changes in extended hours, and why a "closed" market still moves your portfolio's value overnight.

The regular session — and why its edges matter

The regular session is when the full machinery of the central order book operates at maximum participation — the deepest liquidity, the tightest pricing, the most reliable price discovery. Its two edges are structurally special. The opening auction aggregates all orders accumulated since the last close — including reactions to overnight news — into a single crossing that sets the official opening price. The closing auction does the same in reverse and is typically the single largest liquidity event of the day, because index funds and institutional strategies benchmarked to closing prices concentrate their trading there. The auction mechanism exists precisely because transitions are hard: rather than letting the first or last trades happen in a thin scramble, the exchange batches them into one balanced price.

Extended hours: possible, but structurally different

Pre-market and after-hours sessions let orders execute outside regular hours through electronic venues. What changes is not the rules of trading but its texture, and FINRA's investor guidance is blunt about the differences: far fewer participants, which means lower liquidity and depth, wider bid-ask spreads, and more volatile prices; quotes that may differ across venues; and the practical reality that many brokers require limit orders in extended sessions because market orders in thin books can execute at surprising prices. Extended hours exist because news doesn't keep exchange hours — earnings are routinely released just after the close or before the open, and extended trading is where the first repricing happens. Descriptively: the earliest prices after news are also the least liquid ones, a trade-off between immediacy and execution quality that each participant weighs for themselves.

One planet, many clocks

Global investing means global hours. When a European investor's US holdings trade, it is afternoon-to-evening in Europe; when Tokyo opens, New York sleeps. Two practical consequences. First, your portfolio reprices while you sleep: foreign holdings move during their home sessions, and even domestic stocks gap between close and open as news accumulates — the overnight gap is normal machinery, not an anomaly. Second, cross-listed instruments follow their venue's clock: an ETF holding Asian stocks trades all US day, but its underlying holdings' home markets are closed for most of it — the ETF price keeps discovering, the underlying prints don't, which is a structural fact worth knowing when the two seem to disagree. The FX market is the exception that proves the rule: as a global dealer network rather than a single venue, it follows the sun around the banking centres, closing only for the weekend.