How can I figure out how a stock's price would change after I buy shares?
It is unlikely that buying 100 shares will have any effect on a stock's price, unless the stock's average trading volume is incredibly low.  That being said, no matter how many share you buy, there's no way to know what the impact on the price will be, because that's only one factor in how shares are priced.  If anyone could figure out the answer to your question then they'd be extremely rich, because they'd simply watch for big share trades and then buy those stocks on the way up. The market makers who actually execute the trades are the ones who set the prices, and most stocks have multiple market makers trading the stock, so the bid/ask you see is the highest bid and lowest ask.  The market makers set the price based on what the trend of the stock is.  If, for instance, there's a large number of sell orders against a stock, the market makers will start dropping the bid prices as they fill execution orders, and as they see buy orders increase, they'll raise ask prices as they fill execution orders.  The market makers earn the difference between what they paid to buy someone's stock who was selling and what they get from someone else who buys it. This is a simplified explanation, so pro traders, don't beat me up! (grin) So, basically, it takes quite a bit of share volume in one direction or another to affect a stock's price.  I can guarantee a 100-share trade wouldn't even be noticed by market makers. I hope this helps. Good luck! Stock price is based on supply and demand. Unless the stock you are looking to buy usually has very low volume trading 100 shares isn't likely to have any effect on price. There are many companies that have millions or tens of millions of shares trade daily. For stocks like that 100 shares is barely a trivial percentage of the daily volume. For thinly traded stocks you can look at the bid and ask size but even that isn't likely to get you an exact answer. Unless you are trading large volumes your trade will have no effect on the price of shares. It is possible to figure out the next price. Just not for Joe Average. A stock exchange has a orderbook. This has two sides. One side has alle the buyers, how many shares they want, and what they are willing to pay. The other side has all the sellers, how many shares they got, and what price they are willing to accept. If any buyers and sellers match up, their orders are executed, money and shares are exchanged, everyone is happy. So the current asking price (the price you have to pay, to get some shares) is currently 12.46$. Let's say you want 6000 shares, for any price. The orderbook now looks like this: Your order is executed, you get 6000 shares for a total of 74,761$ (5900 * 12,46 + 100 * 12,47$). The order book now looks like this: The new asking price is 12.47$. Congrats, you knew the price in advance. Of course this is simplified, there are millions of entries on both sides, thousands of trades happen every millisecond and you'll have to pay the stock exchange a lot of money to give you all this information in real time.  That's what high frequency traders are doing. They use highly specialised computer systems to exploit differences in stock exchanges all over the world. It's called arbitage. They have to be faster than the other guy. This race has gone on for a few years now, so that the limiting factor starts to become the speed of light. YOU are not going to benefit, or else you would not be asking questions on PERSONAL finance :) "It depends on many factors, but generally, the bid/ask spread will give you an idea. There are typically two ways to buy (or sell) a security: With a limit order, you would place a buy for 100 shares at $30-. Then it's easy, in the worst case you will get your 100 shares at $30 each exactly. You may get lucky and have the price fall, then you will pay less than $30. Of course if the price immediately goes up to say $35, nobody will sell at the $30 you want, so your broker will happily sit on his hands and rake in the commission while waiting on what is now a hail Mary ask. With a market order, you have the problem you mention: The ticker says $30, but say after you buy the first 5 shares at $30 the price shoots up and the rest are $32 each - you have now paid on average $31.9 per share. This could happen because there is a limit order for 5 at $30 and 200 at $32 (you would have filled only part of that 200). You would be able to see these in the order book (sometimes shown as bid/ask spread or market depth). However, the order book is not law. Just because there's an ask for 10k shares at $35 each for your $30 X stock, doesn't mean that by the time the price comes up to $35, the offer will still be up. The guy (or algorithm) who put it up may see the price going up and decide he now wants $40 each for his 10k shares. Also, people aren't obligated to put in their order: Maybe there's a trader who intends to trade a large volume when the price hits a certain level, like a limit order, but he elected to not put in a limit order and instead watch the ticker and react in real time. Then you will see a huge order suddenly come in out of nowhere. So while the order book is informative, what you are asking is actually fundamentally impossible to know fully, unless you can read the minds of every interested trader. As others said, in ""normal"" securities (meaning traded at a major exchange, especially those in the S&P500) you simply can't move the price, the market is too deep. You would need millions of dollars to budge the price, and if you had that much money, you wouldn't be asking here on a QA site, you would have a professional financial advisor (or even a team) that specializes in distributing your large transaction over a longer time to minimize the effect on the market. With crazier stocks, such as OTC and especially worthless penny stocks with market caps of $1 mil or less, what you say is a real problem (you can end up paying multiples of the last ticker if not careful) and you do have to be careful about it. Which is why you shouldn't trade penny stocks unless you know what you're doing (and if you're asking this question here, you don't)."
"Their algorithm may be different (and proprietary), but how I would to it is to assume that daily changes in the stock are distributed normally (meaning the probability distribution is a ""bell curve"" - the green area in your chart).  I would then calculate the average and standard deviation (volatility) of historical returns to determine the center and width of the bell curve (calibrating it to expected returns and implied volaility based on option prices), then use standard formulas for lognormal distributions to calculate the probability of the price exceeding the strike price. So there are many assumptions involved, and in the end it's just a probability, so there's no way to know if it's right or wrong - either the stock will cross the strike or it won't." "He didn't sell in the ""normal"" way that most people think of when they hear the term ""sell."" He engaged in a (perfectly legitimate) technique known as short selling, in which he borrows shares from his broker and sells them immediately. He's betting that the price of the stock will drop so he can buy them back at a lower price to return the borrowed shares back to his broker. He gets to pocket the difference. He had about $37,000 of cash in his account. Since he borrowed ~8400 shares and sold them immediately at $2/share, he got $16,800 in cash and owed his broker 8400 shares. So, his net purchasing power at the time of the short sale was $37,000 + $16,800 - 4800 shares * $2/share. As the price of the stock changes, his purchasing power will change according to this equation. He's allowed to continue to borrow these 8400 shares as long as his purchasing power remains above 0. That is, the broker requires him to have enough cash on hand to buy back all of his borrowed shares at any given moment. If his purchasing power ever goes negative, he'll be subject to a margin call: the broker will make him either deposit cash into his account or close his positions (sell long positions or buy back short positions) until it's positive again. The stock jumped up to $13.85 the next morning before the market opened (during ""before-hours"" trading). His purchasing power at that time was $37,000 + $16,800 - 8400 shares * $13.85/share = -$62,540. Since his purchasing power was negative, he was subject to a margin call. By the time he got out, he had to pay $17.50/share to buy back the 8400 shares that he borrowed, making his purchasing power -$101,600. This $101,600 was money that he borrowed from his broker to buy back the shares to fulfill his margin call. His huge loss was from borrowing shares from his broker. Note that his maximum potential loss is unlimited, since there is no limit to how much a stock can grow. Evidently, he failed to grasp the most important concept of short selling, which is that he's borrowing stock from his broker and he's obligated to give that stock back whenever his broker wants, no matter what it costs him to fulfill that obligation." Stock A last traded at $100. Stock A has 1 million shares outstanding. No seller is willing to sell Stock A for less than $110 a share. One buyer is willing to buy 1 share for $110. The order executes. The buyer pays the seller $110. Stock A's new price is $110. An $110 investment increased the market cap by $10 million. Neat trick (for all who own Stock A). Your understanding of the stock market is absolutely correct theoretically. However there is a lot more to it. A stock on a given day is effected by a lot of factors. These factors could really be anything. For example, if you are buying a stock in an agricultural company and there was no rainfall this year, there is a big chance that your stock will lose value. There is also a chance that a war breaks out tomorrow and due to all the government spending on the war, the economy collapses and effects the prices of stocks. Why does this happen? This happens because bad rainfall or war can get people to lose confidence in a stock market. On the other hand GDP growth and low unemployment rates can make people think positive and increase the demand in a stock driving the prices up. The main factor in the stock market is sentiment(How people perceive certain news). This causes a stock to rise or fall even before the event actually happens. (For example:- Weather pundits predicted good rainfall for next year. That news is already known to people, so if the weather pundit was correct, it might not drive the prices up. However, if the rainfall was way better than people expected it to be it would drive the price up and vice versa.   These are just examples at a basic level. There are a lot of other factors which determine the price of the stock. The best way to look at it(In my personal opinion) is the way Warren Buffet puts it, i.e. look at the stock as a business and see the potential growth over a long period of time.  There will be unexpected events, but in the long run, the business must be profitable. There are various ways to value a company such as Price to earnings ratios, PEG ratios, discounted cash flows and you can also create your own. See what works best for you and record your success/failure ratio before you actually put money in.  Good Luck, "What benefit do I get from buying a share The value of any financial asset is its ability to generate cash in the future, and thus the ""value"" of a share is heavily influenced by the dividends it pays and the equity value.  The equity value can be calculated different ways. Two common ways are to just take ""book"" value, meaning assets - liabilities, or you can look at the projected free cash flows of the company discounted back to the present time. Voting rights don't typically influence a share price except in hostile takeover scenarios (meaning someone buys up a lot of shares to have more influence in company decisions)" A stock is only worth what someone is willing to pay for it. If it trades different values on different days, that means someone was willing to pay a higher price OR someone was willing to sell at a lower price.  There is no rule to prevent a stock from trading at $10 and then $100 the very next trade... or $1 the very next trade. (Though exchanges or regulators may halt trading, cancel trades, or impose limits on large price movements as they deem necessary, but this is beside the point I'm trying to illustrate). Asking what happens from the close of one day to the open of the next is like asking what happens from one trade to the next trade... someone simply decided to sell or pay a different price.  Nothing needs to have happened in between. "You can do several things: After the fact: If you believe the stock will go up, you can buy more stock now, it's what's called ""averaging"". So, you bought 100 at $10, now it's at $7. To gain money from your original investment it needs to raise to over $10. But if you really think it'll go up, you can buy and average. So you buy, say, 100 more stock at $7, now you have 200 shares at $8.50 average so you gain money on your investment when the stock goes over $8.50 instead of $10.  Of course, you risk losing even more money if the stock keeps going down. Before the fact: When you buy stock, set 'triggers'. In most trading houses you can set automatic triggers to fire on conditions you set. When you buy 100 shares at $10, you can set a trigger to automatically sell the 100 shares if it drops below $9, so you limit your losses to 10% (for example)." As said previously, most of the time volume does not affect stock prices, except with penny stocks. These stocks typically have a small volume in the 3 or 4 figure range and because of this they typically experience very sharp rises and drops in stock prices, contrasting normal stocks that go up and down constantly every minute. Volume is not one thing you should be looking at when analyzing a stock in most cases, since it is simply the number of people of trades made in a day. That has no effect on the value of the company, whereas looking at P/E ratios, dividend growth, etc all can be analyzed to see if a company is growing and is doing well in its field. If I buy an iPhone, it doesn't matter if 100 other people or 100,000 other people have bought it as well, since they won't really affect my experience with the product. Whereas the type of iPhone I buy will. "You are probably going to hate my answer, but... If there was an easy way to ID stocks like FB that were going to do what FB did, then those stocks wouldn't exist and do that because they would be priced higher at the IPO. The fact is there is always some doubt, no one knows the future, and sometimes value only becomes clear with time. Everyone wants to buy a stock before it rises right? It will only be worth a rise if it makes more profit though, and once it is established as making more profit the price will be already up, because why wouldn't it be? That means to buy a real winner you have to buy before it is completely obvious to everyone that it is going to make more profit in the future, and that means stock prices trade at speculative prices, based on expected future performance, not current or past performance. Now I'm not saying past and future performance has nothing in common, but there is a reason that a thousand financially oriented websites quote a disclaimer like ""past performance is not necessarily a guide to future performance"". Now maybe this is sort of obvious, but looking at your image, excluding things like market capital that you've not restricted, the PE ratio is based on CURRENT price and PAST earnings, the dividend yield is based on PAST publications of what the dividend will be and CURRENT price, the price to book is based on PAST publication of the company balance sheet and CURRENT price, the EPS is based on PAST earnings and the published number of shares, and the ROI and net profit margin in based on published PAST profits and earnings and costs and number of shares. So it must be understood that every criteria chosen is PAST data that analysts have been looking at for a lot longer than you have with a lot more additional information and experience with it. The only information that is even CURRENT is the price. Thus, my ultimate conclusive point is, you can't based your stock picks on criteria like this because it's based on past information and current stock price, and the current stock price is based on the markets opinion of relative future performance. The only way to make a good stock pick is understand the business, understand its market, and possibly understand world economics as it pertains to that market and business. You can use various criteria as an initial filter to find companies and investigate them, but which criteria you use is entirely your preference. You might invest only in profitable companies (ones that make money and probably pay regular dividends), thus excluding something like an oil exploration company, which will just lose money, and lose it, and lose some more, forever... unless it hits the jackpot, in which case you might suddenly find yourself sitting on a huge profit. It's a question of risk and preference. Regarding your concern for false data. Google defines the Return on investment (TTM) (%) as: Trailing twelve month Income after taxes divided by the average (Total Long-Term Debt + Long-Term Liabilities + Shareholders Equity), expressed as a percentage. If you really think they have it wrong you could contact them, but it's probably correct for whatever past data or last annual financial results it's based on." It depends to some extent on how you interpret the situation, so I think this is the general idea. Say you purchase one share at $50, and soon after, the price moves up, say, to $55. You now have an unrealized profit of $5. Now, you can either sell and realize that profit, or hold on to the position, expecting a further price appreciation. In either case, you will consider the price change from this traded price, which is $55, and not the price you actually bought at. Hence, if the price fell to $52 in the next trade, you have a loss of $3 on your previous profit of $5. This (even though your net P&L is calculated from the initial purchase price of $50), allows you to think in terms of your positions at the latest known prices. This is similar to a Markov process, in the sense that it doesn't matter which route the stock price (and your position's P&L) took to get to the current point; your decision should be based on the current/latest price level. In order: A seller of the stock (duh!). You don't know who or why this stock was sold. It could be any reason, and is of no concern of yours. It doesn't matter. Investors (pension funds, hedge funds, individual investors, employees, management) sell stock for many reasons: need cash, litigation, differing objectives, sector rotation, etc. To you, this does not matter. Yes, it does affect stock market prices: If you were not willing to buy that amount of shares, and there were no other buyers at that price, the seller would likely choose to lower the price offered. By your purchase, you are supporting the price. In order to see whether you can buy or sell some given quantity of a stock at the current bid price, you need a counterparty (a buyer) who is willing to buy the number of stocks you are wishing to offload. To see whether such a counterparty exists, you can look at the stock's order book, or level two feed. The order book shows all the people who have placed buy or sell orders, the price they are willing to pay, and the quantity they demand at that price. Here is the order book from earlier this morning for the British pharmaceutical company, GlaxoSmithKline PLC.  Let's start by looking at the left-hand blue part of the book, beneath the yellow strip. This is called the Buy side. The book is sorted with the highest price at the top, because this is the best price that a seller can presently obtain. If several buyers bid at the same price, then the oldest entry on the book takes precedence. You can see we have five buyers each willing to pay 1543.0 p (that's 1543 British pence, or £15.43) per share. Therefore the current bid price for this instrument is 1543.0. The first buyer wants 175 shares, the next, 300, and so on. The total volume that is demanded at 1543.0p is 2435 shares. This information is summarized on the yellow strip: 5 buyers, total volume of 2435, at 1543.0. These are all buyers who want to buy right now and the exchange will make the trade happen immediately if you put in a sell order for 1543.0 p or less. If you want to sell 2435 shares or fewer, you are good to go. The important thing to note is that once you sell these bidders a total of 2435 shares, then their orders are fulfilled and they will be removed from the order book. At this point, the next bidder is promoted up the book; but his price is 1542.5, 0.5 p lower than before. Absent any further changes to the order book, the bid price will decrease to 1542.5 p. This makes sense because you are selling a lot of shares so you'd expect the market price to be depressed. This information will be disseminated to the level one feed and the level one graph of the stock price will be updated. Thus if you have more than 2435 shares to sell, you cannot expect to execute your order at the bid price in one go. Of course, the more shares you are trying to get rid of, the further down the buy side you will have to go. In reality for a highly liquid stock as this, the order book receives many amendments per second and it is unlikely that your trade would make much difference. On the right hand side of the display you can see the recent trades: these are the times the trades were done (or notified to the exchange), the price of the trade, the volume and the trade type (AT means automatic trade).  GlaxoSmithKline is a highly liquid stock with many willing buyers and sellers. But some stocks are less liquid. In order to enable traders to find a counterparty at short notice, exchanges often require less liquid stocks to have market makers. A market maker places buy and sell orders simultaneously, with a spread between the two prices so that they can profit from each transaction. For instance Diurnal Group PLC has had no trades today and no quotes. It has a more complicated order book, enabling both ordinary buyers and sellers to list if they wish, but market makers are separated out at the top. Here you can see that three market makers are providing liquidity on this stock, Peel Hunt (PEEL), Numis (NUMS) and Winterflood (WINS). They have a very unpalatable spread of over 5% between their bid and offer prices. Further in each case the sum total that they are willing to trade is 3000 shares. If you have more than three thousand Dirunal Group shares to sell, you would have to wait for the market makers to come back with a new quote after you'd sold the first 3000. Yes, somebody could buy the shares, receive the dividend, and then sell the shares back. However, the price he would get when he sells the shares back is, ignoring other reasons for the price to change, exactly the amount he paid minus the dividend. Knowing the answer to this question is generally not as useful as it may seem.  The stock's current price is the consensus of thousands of people who are looking at the many relevant factors (dividend rate, growth prospects, volatility, risk, industry, etc.) that determine its value.  A stock's price is the market's valuation of the cash flows it entitles you to in the future.  Researching a stock's value means trying to figure out if there is something relevant to these cash flows that the market doesn't know about or has misjudged.  Pretty much anything we can list for you here that will affect a stock's price is something the market knows about, so it's not likely to help you know if something is mispriced.  Therefore it's not useful to you. If you are not a true expert on how important the relevant factors are and how the market is reacting to them currently (and often even if you are), then you are essentially guessing.  How likely are you to catch something that the thousands of other investors have missed and how likely are you to miss something that other investors have understood?  I don't view gambling as inherently evil, but you should be clear and honest with yourself about what you are doing if you are trying to outperform the market. As people become knowledgeable about and experienced with finance, they try less and less to be the one to find an undervalued stock in their personal portfolio.  Instead they seek to hold a fully diversified portfolio with low transactions costs and build wealth in the long term without wasting time and money on the guessing game.  My suggestion for you is to transition as quickly as you can to behave like someone who knows a lot about finance. The average price would be $125 which would be used to compute your basis. You paid $12,500 for the stock that is now worth $4,500 which is a loss of $8,000 overall if you sell at this point.