Pre & Post-market trading session

In addition to the regular trading sessions, US stocks also have extended pre-market and post-market trading sessions. Due to the 1-hour spread between daylight saving time and standard time in the United States, the trading sessions in GMT+8 are adjusted by 1 hour correspondingly. Daylight saving time begins on the second Sunday in March each year, and standard time begins on the first Sunday in November.

Pre & Post-market price mechanism

The US stock exchanges do not have a unified official price for the pre-market and post-market prices. However, brokerage firms adopt the last done price to update the pre & post-market High/Low/Last Done according to the rules.

While the exchanges do not provide official prices for extended trading sessions, official guidelines are available. We offer pre & post-market prices to US stocks based on the guidelines from official Nasdaq and NYSE documents.

One of the most important rules is: odd lot (including fractional share) transactions do not affect High/Low/Last Done price.

The following is a screenshot from the exchange:

Therefore, it is possible that the last done price is inconsistent with the pre-market and post-market prices.

In addition, different brokers may apply this rule differently, resulting in different pre-market and post-market prices displayed on different platforms. You can check the specific transaction details page to determine the price of the last "non-odd lot transaction".