Pre-Market and Post-Market Quotes Introduction
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 the 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-market | Intraday (regular trading session) | Post-market | |
|---|---|---|---|
| EST | 4:00 - 9:30 | 9:30 - 16:00 | 16:00 - 20:00 |
| BJT/HKT/SGT (GMT+8) (EST: daylight saving time) | 16:00 - 21:30 | 21:30 - 04:00(+1) | 04:00 - 08:00 |
| BJT/HKT/SGT (GMT+8) (EST: standard time) | 17:00 - 22:30 | 22:30 - 05:00(+1) | 05:00 - 09:00 |
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 sale 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 transactions DO NOT UPDATE High/Low/Last Sale.
The following is a screenshot from the exchange:
For National BBO, we follow the above rules and do not update odd lot transaction prices to the pre-market/post-market last-sale prices. Therefore, it is possible that "the last done price is inconsistent with the pre-market and post-market prices", which is normal.
In addition, different brokers may apply this rule differently, resulting in different pre-market and post-market prices displayed on different platforms. We can check the specific transaction details page to determine the price of the last "non-odd lot transaction".
