Why can it be a bad idea to buy stocks after hours?
There are several reasons it is not recommended to trade stocks pre- or post-market, meaning outside of RTH (regular trading hours). Since your question is not very detailed I have to assume you trade with a time horizon of at least more than a day, meaning you do not trade intra-day. If this is true, all of the above points are a non-issue for you and a different set of points becomes important. As a general rule, using (3) is the safest regardless of what and how you trade because you get price guarantee in trade for execution guarantee. In the case of mid to longer term trading (1 week+) any of those points is viable, depending on how you want to do things, what your style is and what is the most comfortable for you. A few remarks though: (2) are market orders, so if the open is quite the ride and you are in the back of the execution queue, you can get significant slippage. (1) may require (live) data of the post-market session, which is often not easy to come by for the entire US stock universe. Depending on your physical execution method (phone, fax, online), you may lack accurate information of the post-market. If you want to execute orders based on RTH and only want to do that after hours because of personal schedule constraints, this is not really important. Personally I would always recommend (3), independent of the use case because it allows you more control over your orders and their fills. TL;DR: If you are trading long-term it does not really matter. If you go down to the intra-day level of holding time, it becomes relevant. "During market hours, there are a lot of dealers offering to buy and sell all exchange traded stocks. Dealers don't actually care about the company's fundamentals and they set their prices purely based on order flow. If more people start to buy than sell, the dealer notices his inventory going down and starts upping the price (both his bid and ask). There are also traders who may not be ""dealers"", but are willing to sell if the price goes high enough or buy if the price goes low enough. This keeps the prices humming along smoothly. During normal trading hours, if you buy something and turn around and sell it two minutes later, you'll probably be losing a couple cents per share. Outside normal market hours, the dealers who continue to have a bid and ask listed know that they don't have access to good price information --  there isn't a liquid market of continuous buying and selling for the dealer to set prices he considers safe. So what does he do? He widens the spread. He doesn't know what the market will open tomorrow at and doesn't know if he'll be able to react quickly to news. So instead of bidding $34.48 and offering at $34.52, he'll move that out to $33 and $36. The dealer still makes money sometimes off this because maybe some trader realized that he has options expiring tomorrow, or a short position that he's going to get a margin call on, or some kind of event that pretty much forces him to trade. Or maybe he's just panicking and overreacting to some news. So why not trade after hours? Because there's no liquidity, and trading when there's no liquidity costs you a lot." Unless you want to be a short term day trader, then it is not foolish to be an end of day trader. If you are looking to be a medium to long term trader/investor then it is quite acceptable to put orders in after market close. Some would say it is even less risky, because you are not watching the price fluctuate up and down and letting your emotions getting the best of you. The sentiment is because between closing and opening a lot can happen, and between opening and the time your order actually goes through, even more can happen.  An after-hours trade has an extra amount of short-term risk attached; the price of a stock at the opening bell is technically the same as its price as of the closing the previous trading day, but within a tenth of a second, which is forever in a computerized exchange, that price may move drastically one way or the other, based on news and on other markets. The sentiment, therefore, is simple; if you're trading after-hours, you're trading risky. You're not trading based on what the market's actually doing, you're trading based on what you think the market will do in the morning, and there's still more math going on every second in the privately-held supercomputers in rented cubes in the NYSE basement than you could do all night, digesting this news and projecting what it's going to do to the stocks. Now, if you've done your homework and the stock looks like a good long-term buy, with or without any after-hours news, then place the order at 3 in the morning; who cares what the stock's gonna do at the opening bell. You're gonna hold that stock for the next ten years, maybe; what it does in 5 seconds of opening turmoil is relatively minor compared to the monthly trends that you should be worrying about.
"The psychology of investing is fascinating. I buy a stock that's out of favor at $10, and sell half at a 400% profit, $50/share. Then another half at $100, figuring you don't ever lose taking a profit. Now my Apple shares are over $500, but I only have 100. The $10 purchase was risky as Apple pre-iPod wasn't a company that was guaranteed to survive.  The only intelligent advice I can offer is to look at your holdings frequently, and ask, ""would I buy this stock today given its fundamentals and price?"" If you wouldn't buy it, you shouldn't hold it. (This is in contrast to the company ratings you see of buy, hold, sell. If I should hold it, but you shouldn't buy it to hold, that makes no sense to me.) Disclaimer - I am old and have decided stock picking is tough. Most of our retirement accounts are indexed to the S&P. Maybe 10% is in individual stocks. The amount my stocks lag the index is less than my friends spend going to Vegas, so I'm happy with the results. Most people would be far better off indexing than picking stocks." One of the fundamental of technical analysis suggests that holding a security overnight represents a huge commitment.  Therefore it would follow that traders would tend to close their positions prior to market close and open them when it opens. You can make a purchase at the after market price by sending an order that gets executed in after market. Often times these are called Extended orders, or EXT. With an EXT limit order it will place the bid on the after market hours order book. If you get filled, then you have the shares.  This is the answer. The two answers so far are right, but there's a third factor - for many stocks, there's after hours trading. So the official 4PM close is not what the stock's last trade was when they open again. Regardless, even that after hour price is not the starting point as Muro points out. "But speculation is absolutely intended to happen, and is considered necessary for healthy a investment environment.  What I am saying, however, is that this desire to rid the world of HFT appears to be moral rather than logical. There is very little reason to eliminate HFT as it stands, although there appears to be a propensity for very emotional responses to the basic concept. Ones I can appreciate. However I am suggesting they are misguided as the people who should be upset with HFT are the hedge fund managers and day traders they are outwitting, not you or me who buy and sell shares on a whim every so often. If you want to ban day traders that is a separate argument I don't want to go into.  The idea that these computer algorithms are all set to ""sell,sell,sell"" is provably nonsensical. If that were the case, all of the HFT participants would have gone massively bankrupt during the flash crashes. Also, it is quite patently the case that somebody has to be buying in order for anybody to sell. Saying ""this is what caused some of the crashes"" is just your desire for a simple explanation. It must have been more complex than this, and to my knowledge none of these crashes have been adequately explained although some poorly designed algorithms have been implicated. Note that in one of these cases IIRC a fund closed its doors due to the losses, and the market was largely unaffected. So it seems like a problem that self corrects in this case, and one that only *harms* the participant that erred.  Also, to correct a basic misunderstanding, selling happens all of the time, and does not inherently drive the price down. There are by definition an *equal number of sales to purchases*. What drives the price down is *the people buying being willing to pay less*.  EDIT: as another aside, a point I have made elsewhere and seems suitable to make here: flash crashes, whilst causing panic, are again something only the professional intra-day trading community are likely to be affected by. Their very name implies so. The reason being that anybody investing based on the *long term investment potential* of a company will only benefit in the temporary drop in price, as they can purchase more of the company at a bargain price. Any intelligent investor will not be fazed by the drop in price, as price has *no bearing on a company's real value*, and stocks do tend towards this value over time, whatever happens over the short term. The only case in which it could is if the company owns a large portfolio of stock that itself devalues dramatically that they intended to sell and as a result experience cash flow problems. This is so incredibly unlikely with a flash crash as to be ignored." This can arise with very thinly traded stocks for large blocks of shares. If the market only has a few thousand dollars available at between 8.37 and 12.5 the price is largely meaningless for people who want to invest in hundreds of thousands/millions of dollars worth, as the quoted price can't get them anywhere near the number of shares they want. How liquid is the stock in question? It is a general truism but the reasons are that the rules change dramatically when you simply have more capital. Here are some examples, limited to particular kinds of markets: Under $2,000 in capital Nobody is going to offer you a margin account, and if you do get one it isn't with the best broker on commissions and other capabilities. So this means cash only trading, enjoy your 3 business day settlement periods. This means no shorting, confining a trader to only buy and hold strategies, making them more dependent on luck than a more capable trader. This means it is more expensive to buy stock, since you have to put down 100% of the cash to hold a share, whereas someone with more money puts down less capital to hold the exact same number of shares. This means no covered options strategies or spreads, again limiting the market directions where a trader could earn Under $25,000 in capital In the stock market, the pattern day trader rule applies to retail margin accounts with a balance under $25,000 and this severally limits the kinds of trades you are able to take because of the limit in the number of trades you can take in a given time period. Forget managing a multi-leg option position when the market isn't moving your direction. Under $125,000 in capital Worse margin rules. You excluded portfolio margin from your post, but it is a key part of the answer Over $1,000,000 in capital Participate in private placements, regulation D offerings reserved for accredited investors. These days, as buy and hold investments, these generally have more growth potential than publicly traded offerings. Over $5,000,000 in capital You can easily get the compliance and risk manager to turn the other way on margin rules. This is not conjecture, leverage up to infinity, try not to bankrupt yourself and the trading firm. There are classes of 'traders' who close their positions out every evening, not just on fridays.  But their are other types of businesses who trade shortly before or nearly right at market close with both buys and sells  There are lots of theories as to how the market behaves at various times of day, days of the week, months of the year.  There are some few patterns that can emerge but in general they don't provide a lot of 'lift' above pure random chance, enough so that if you 'bet' on one of these your chances of being wrong are only very slightly different from being right, enough so that it's not really fair to call any of them a 'sure thing'.  And since these events are often fairly widely spaced, it's difficult to play them often enough to get the 'law of large numbers' on your side (as opposed to say card-counting at a blackjack table) which basically makes betting on them not much different from gambling TD will only sell the stock for you if there's a buyer. There was a buyer, for at least one transaction of at least one stock at 96.66. But who said there were more? Obviously, the stocks later fell, i.e.: there were not that many buyers as there were sellers. What I'm saying is that once the stock passed/reached the limit, the order becomes an active order. But it doesn't become the only active order. It is added to the list, and to the bottom of that list. Obviously, in this case, there were not enough buyers to go through the whole list and get to your order, and since it was a limit order - it would only execute with the limit price you put. Once the price went down you got out of luck.  That said, there could of course be a possibility of a system failure. But given the story of the market behavior - it just looks like you miscalculated and lost on a bet. One of the biggest laws in economics is that if an opportunity is very profitable and is very easily exploitable even by complete beginners, then it will very soon stop being profitable. That's how the market works. If you buy stock when it is at the lowest, then you are making money, but most of the time someone else is losing money. And if there was a magic hour of the day when buying would be the most profitable, then soon everybody would want to buy at that time and no one would want to sell anything, so the scheme would collapse. "The technical term for it is ""timing the market"" and if you can pull it off correctly, you will do quite well. The problem is that it is almost impossible to consistently do well. If it were that easy there would be a lot of billionaires walking around. Even Wall street experts haven't been able to predict the market that well. This idea is almost universally considered a bad idea. Consider this: When has the stock dropped low enough that you are ""buying low"" and let's say you do buy low and it doubles in a month. When do you get out? What if you are wrong and it doubles again? Or if it drops 10% do you keep waiting? This strategy is rife with problems." "You have heard the old adage ""Buy low, sell high"", right? That sounds so obvious that you'd have to wonder why they would ever bother coining such an expression. It should rank up there with ""Don't walk in front of a moving car"" on the Duh scale of advice. Well, your question demonstrates exactly why it isn't quite so obvious in the real world and that people need to be reminded of it.  So, in your example, the stock prices are currently low (relative to what they have been). So per that adage, do you sell or buy when prices are low? Hint: It isn't sell. Yes. Your gut is going to tell you the exact opposite thanks to the fact that our brains are unfortunately wired to make us susceptible to the loss aversion fallacy. When the market has undergone a big drop is the WORST time to stop contributing (buying stocks).  This example might help get your brain and gut to agree a little more easily: If you were talking about any other non-investment commodity, cars for instance.  Your question equates to.. I really need a car, but the prices have been dropping like crazy lately.    Maybe I should wait until the car dealers start raising their prices again before I buy one. Dollar Cost Averaging As littleadv suggested, if you have an automatic payroll deduction for your retirement account, you are getting the benefit of Dollar Cost Averaging. Because you are investing the same amount on a scheduled interval, you are buying more shares when they are cheap and fewer when they are expensive. It is like an automatic buy low strategy is built into the account. The alternative, which you are implying, is a market timing strategy. Under this strategy, instead of investing regularly you try to get in and out of investments right before they go up/drop. There are two MAJOR flaws with this approach:   1) Your brain will work against you (see above) and encourage you to do the exact opposite of what you should be doing.   2) Unless you are clairvoyant, this strategy isn't much better than gambling. If you are lucky it can work, but because of #1, the odds are stacked against you." you need minimum of 25k otherwise youll reach a limit. you have to wait 3 days for the sale to clear unless youre on margin. dont buy anything based on idiots on twitter or the internet. however, theres some good people to follow though that know what theyre doing.  dont listen to this guy saying that etrade or those platforms arent fast enough. they all offer level 2 prices so i dont know what hes talking about. successful day traders arent buying and selling a stock every single day. theres not always something to buy and sell...unless youre just gambling, and in that case just go to the casino and lose your money there. There are several problems with your reasoning: if I buy one share of GOOGLE now for $830, I could have $860 within the end of tonight -- totally possible and maybe even likely. You can do the same thing with 1,000,000 shares of google, and it's just as likely to go down as go up.   if I were to invest $1,000.00 in gold to have $1,000.00 worth of gold, it's no different than keeping $1,000.00 in cash It's VERY different.  Gold can be just as volatile as stocks, so it certainly is different as just keeping it in cash. Benefits of a larger portfolio: I'm currently using Halifax. Pros: Cons: I'm might start using TD Waterhouse in future, as they claim to have no admin charge.