After-Hours Trading

After-hours trading is trading outside an exchange's regular session. In the United States, brokers offer extended sessions from 4am to 9.30am and 4pm to 8pm Eastern time, where earnings announcements are traded the moment they are released. The ASX has no equivalent retail session: the market runs a pre-open phase from 7am Sydney time, where orders queue for the 10am opening auction, and closes at 4pm with a closing auction shortly after. Between the close and the next open, the ASX retail investor simply waits.

The waiting is not costless. Australian-listed companies report overnight or during the day, global markets move while Sydney sleeps, and all of it lands in the opening auction as a gap - the price difference between yesterday's close and today's auction print. The gap is the after-hours session the ASX does not run, executed without you. The market vs limit order entry covers the order types the auction consumes.

The session structure is the mechanism. The ASX pre-open runs from 7am, when orders are accepted and queued without trading; at 10am the opening auction matches the queue at a single price that balances the book. The main session trades through to 4pm, and the closing auction sets the official close the same way. There is no retail after-hours phase: the US brokers' 4am-to-9.30am and 4pm-to-8pm sessions have no ASX equivalent, and the overnight hours are where the world moves without the local market.

The gap is the second mechanism. A US earnings shock, an RBA decision at 2.30pm or an overnight commodity move reprices the stock while the ASX is closed, and the opening auction prints the new price as a gap. A stock that closed at $10 and opens at $9.60 has repriced 4 percent in a session nobody traded - the after-hours move was real, and it was executed by the auction, not by the holder. The volatility entry covers the swings, and the gap is their overnight version.

The limited exceptions are the third mechanism. ASX's Centrepoint session - a midday matching auction launched as a pilot - and offshore-listed ETFs on the ASX give partial exposure, but neither is an after-hours market. Some global brokers offer US extended-hours sessions to Australian clients, which is genuine after-hours trading in the American market - the news is traded live, in a session with thin liquidity and wide spreads.

For an Australian reader, the after-hours question is about what happens between 4pm and 10am. Those are the hours the ASX does not run and the world does. Overnight earnings, US market moves and commodity shocks land in the opening auction as a gap. The gap is priced without any input from the holder.

A stop loss does not protect against it: the exchange matches the auction at the new price, not your stop. The market vs limit order entry covers the order types the auction consumes. The gap is the reason overnight risk is priced separately from intraday risk.

A colleague named Brent (yes, that Brent) held a miner through a 2.30pm RBA decision and an overnight iron ore fall. He set a stop loss 5 percent under the close, and the stock gapped 7 percent at the open. The stop filled at the auction price, 2 percent below his line, and the protection was a 5 percent discount on the gap.

The highest-leverage thing most Australians can do is size overnight positions knowing the gap is untradeable. Place limit orders into the opening auction rather than market orders that take the print. The stop loss calculator prices the intraday arithmetic; the gap sits outside it.