Q: Price movements in the US after-hours market have had me puzzled for months. I have noticed *unexplained* spikes in share prices in after-hours trading. As a simple test , I set up price alerts on a dozen Nasdaq-listed companies and asked Schwab’s platform to alert me if the prices fell by significant percentages— amounts that were , say, 20% below closing prices, and that price drop was not attributable to earnings releases or other news .
To my surprise, the platform sent me far more alerts than I expected. All alerts were after hours.
Here is an example on trading in NVDA after 5 PM November 8, 2023. NVDA traded almost 35 million shares during the day within the price range: US$459.68 – US$468.67 (a tight range of 0.21% , from high to low).
At 5:17 PM I received an alert that NVDA had fallen below US$393. I checked on nasdaq.com for the after-hours trading. The low price shows is shown at 5:35 PM as US$228.29, after which shares went back to US$461, apparently soon after.
The above is not necessarily an isolated case, going by my alerts being triggered. Notwithstanding that my test is simplistic , I ask if you have any knowledge of how, and why this happens.
(Screen shots below but I am not sure if your system will show images).
To my surprise, the platform sent me far more alerts than I expected. All alerts were after hours.
Here is an example on trading in NVDA after 5 PM November 8, 2023. NVDA traded almost 35 million shares during the day within the price range: US$459.68 – US$468.67 (a tight range of 0.21% , from high to low).
At 5:17 PM I received an alert that NVDA had fallen below US$393. I checked on nasdaq.com for the after-hours trading. The low price shows is shown at 5:35 PM as US$228.29, after which shares went back to US$461, apparently soon after.
The above is not necessarily an isolated case, going by my alerts being triggered. Notwithstanding that my test is simplistic , I ask if you have any knowledge of how, and why this happens.
(Screen shots below but I am not sure if your system will show images).