How will the after market affect the open of the market tomorrow?
In general a stock can open at absolutely any price with no regard for the closing price or after hours price the previous day. The opening price will be determined by the best bid and offer made by people who decide to trade the next day.  Some of the those people may have put orders in on a prior day that are still on the books and matter, but there's a lot of time overnight for people to cancel orders and enter new ones, which is especially likely to happen if there was substantive news overnight. As for what you can do in your case, you have the same options that you always had:  Sell or hold.  If you're selling, you can sell after hours, in the pre-open hours, or during the trading day.  There's nothing we can say about this case that's really any different than we can say about any other stock on any other day.
Graphs are nothing but a representation of data. Every time a trade is made, a point is plotted on the graph. After points are plotted, they are joined in order to represent the data in a graphical format.  Think about it this way.  1.) Walmart shuts at 12 AM. 2.)Walmart is selling almonds at $10 a pound.  3.) Walmart says that the price is going to reduce to $9 effective tomorrow. 4.) You are inside the store buying almonds at 11:59 PM.  5.) Till you make your way up to the counter, it is already 12:01 AM, so the store is technically shut. 6.) However, they allow you to purchase the almonds since you were already in there.  7.) You purchase the almonds at $9 since the day has changed. 8.) So you have made a trade and it will reflect as a point on the graph. 9.) When those points are joined, the curves on the graph will be created. 10.) The data source is Walmart's system as it reflects the sale to you. ( In your case the NYSE exchange records this trade made). Buying a stock is just like buying almonds. There has to be a buyer. There has to be a seller. There has to be a price to which both agree. As soon as all these conditions are met, and the trade is made, it is reflected on the graph. The only difference between the graphs from 9 AM-4 PM, and 4 PM-9 AM is the time. The trade has happened regardless and NYSE(Or any other stock exchange) has recorded it! The graph is just made from that data. Cheers. "There is a white paper on ""The weekend effect of equity options"" it is a good paper and shows that (for the most part) option values do lose money from Friday to Monday. Which makes sense because it is getting closer to expiration. Of course this not something that can be counted on 100%.  If there is some bad news and the stock opens down on a Monday the puts would have increased and the calls decreased in value. Article Summary (from the authors): ""We find that returns on options on individual equities display markedly lower returns over weekends (Friday close to Monday close) relative to any other day of the week. These patterns are observed both in unhedged and delta-hedged positions, indicating that the effect is not the result of a weekend effect in the underlying securities. We find even stronger weekend effects in implied volatilities, but only after an adjustment to quote implied volatilities in terms of trading days rather than calendar days.""  ""Our results hold for puts and calls over a wide range of maturities and strike prices, for both equally weighted portfolios and for portfolios weighted by the market value of open interest, and also for samples that include only the most liquid options in the market. We find no evidence of a weekly seasonal in bid-ask spreads, trading volume, or open interest that could drive the effect. We also find little evidence that weekend returns are driven by higher levels of risk over the weekend.  ""The effect is particularly strong over expiration weekends, and it is also present to a lesser degree over mid-week holidays. Finally, the effect is stronger when the TED spread and market volatility are high, which we interpret as providing support for a limits to arbitrage explanation for the persistence of the effect."" - Christopher S. Jones & Joshua Shemes You can read more about this at this link for Memphis.edu" Sometimes the market has to be left alone. Too much interference of the policy makers to stabilize the falling market can actually result in a major crisis. Every change stabilises after sometime and it is also applicable in the Forex trading market. So, the eager investors should learn to have some patience and wait for the market to stabilise itself rather than make random predictions on the policies released by policy makers "The risk of market orders depends heavily on the size of the market and the exchange. On big exchange and a security which is traded in hue numbers you're likely that there are enough participants to give you a ""fair"" price. Doing a market order on a security which is hardly dealed you might make a bad deal. In Germany Tradegate Exchange and the sister company the bank Tradegate AG are known to play a bit dirty: Their market is open longer than Frankfurt (Xetra) and has way lower liquidity. So it can happen that not all sell or buy orders can be processes on the Exchange and open orders are kept. Then Tradegate AG steps in with a new offer to full-fill these trades selling high or buying low. There is a German article going in details on wiwo.de either German or via Google Translate" "This is the best tl;dr I could make, [original](https://www.bloomberg.com/news/articles/2017-08-22/hong-kong-braces-for-storm-hato-stock-trading-may-be-disrupted) reduced by 73%. (I'm a bot) ***** &gt; Hong Kong upgraded the storm warning to the highest for the first time in five years and canceled its morning trading session as Severe Typhoon Hato drew closer to the financial center.  &gt; Should the signal remain in effect by noon, trading on the world&amp;#039;s fourth-largest equity market will be scrapped for the day, according to Hong Kong Exchanges &amp; Clearing Ltd. rules.  &gt; At 9 a.m., Severe Typhoon Hato was centered about 80 kilometers south of Hong Kong, the Observatory said.   ***** [**Extended Summary**](http://np.reddit.com/r/autotldr/comments/6vgq2t/hong_kong_delays_morning_trading_as_typhoon_hato/) | [FAQ](http://np.reddit.com/r/autotldr/comments/31b9fm/faq_autotldr_bot/ ""Version 1.65, ~196625 tl;drs so far."") | [Feedback](http://np.reddit.com/message/compose?to=%23autotldr ""PM's and comments are monitored, constructive feedback is welcome."") | *Top* *keywords*: **Hong**^#1 **Kong**^#2 **close**^#3 **Typhoon**^#4 **trading**^#5" It is called the Monday Effect or the Weekend Effect. There are a number of similar theories including the October Effect and January Effect. It's all pretty much bunk. If there were any truth to traders would be all over it and the resulting market forces would wipe it out. Personally, I think all technical analysis has very little value other than to fuel conversations at dinner parties about investments. You might also consider reading about Market efficiency to see further discussion about why technical approaches like this might, but probably don't work. It depends completely on the current order book for that security.  There is literally no telling how that buy order would move the price of a stock in general. "NASDAQ has Pre and After market : NASDAQ Trading Schedule Regular Trading Session Schedule The NASDAQ   Stock Market Trading Sessions (Eastern Time) Pre-Market Trading Hours from 4:00 a.m. to 9:30 a.m.   Market Hours from 9:30 a.m. to 4:00 p.m.   After-Market Hours from 4:00 p.m. to 8:00 p.m.   Quote and order-entry from 4:00 a.m. to 8:00 p.m.   Quotes are open and firm from 4:00 a.m. to 8:00 p.m. You can trade in Pre/After Market but liquidity is very low. If an ""unexpected world events"" occurs, the volume/liquidity will most certainly increase. Another example is the Forex Market that's open 24/7 around the world. As one major forex market closes, another one opens. According to GMT,   for instance, forex trading hours move around the world like this:   available in New York between 01:00 pm – 10:00 pm GMT; at 10:00 pm GMT   Sydney comes online; Tokyo opens at 00:00 am and closes at 9:00 am   GMT; and to complete the loop, London opens at 8:00 am and closes at   05:00 pm GMT. This enables traders and brokers worldwide, together   with the participation of the central banks from all continents, to   trade online 24 hours a day. src" You typically need to specify that you want the GTC order to be working during the Extended hours session. I trade on TD Ameritrade's Thinkorswim platform, and you can select DAY, GTC, EXT or GTC_EXT. So in your case, you would select GTC_EXT. What if there is only one trading day and the volume is smaller than   the open interest on that one trading day. This is assuming there is   no open interest before that day? I pulled this from a comment. This can't happen. We have zero open interest on day one. On day 2, I buy 10 contracts. Volume is 10 and now open interest is also 10. Tomorrow, if I don't sell, open interest starts at 10 and will rise by whatever new contracts are traded.   This is an example. I removed the stock name. This happens to be the Jan'17 expiration. The 10 contract traded on the $3 strike happen to be mine. You can see how open interest is cumulative, representing all outstanding contracts. It's obvious to me the shares traded as high as $5 at some point which created the interest (i.e. the desire) to trade this strike. Most activity tends to occur near the current price. Is it possible that mutual funds account for a significant portion of this volume. Investors may decide to buy or sell anytime within a 24 hour period, but the transaction only happened at the close of the market. Therefore at 3:59 pm the mutual fund knows if they will be buying or selling stocks that day.  As nws pointed out the non-market hours are longer and therefore accumulate more news event. Some financial news is specifically given during the time the market is closed. Therefore the reaction to that news has to either be in the morning when the market opens or in the late afternoon if they are trying to anticipate the news.  Also in the US market the early morning trader may be reacting to European market activities. "4PM is the market close in NYC, so yes, time looks good.  If ""out of the money,"" they expire worthless.  If ""in the money,"" it depends on your broker's rules, they can exercise the option, and you'll need to have the money to cover on Monday or they can do an exercise/sell, in which case, you'd have two commissions but get your profit.  The broker will need to tell you their exact procedure, I don't believe it's universal." No, it's not even remotely accurate in the current sense. Both markets have counterparties directly executing against one another, and both have auctions. The auction mechanics are different (with NYSE's Specialist/DMM model) but during normal market hours there isn't much difference. The dynamics of different contracts and liquidity can be quite different on the last day on the month and for intraday trade make sure you use bid-ask data as opposed to historical trades.  I'm not saying whether it works or not, but im just giving you ideas to improve your testing. Thank you for the comment,  New markets open and close all the time, its interesting seeing the new characters appear here as a certain country demands a supply of a new certain product. You feel a bit ahead of the trends here sometimes in that respect.  Thanks