How Is the Price of a Stock Determined? [duplicate]
"The market price of a stock is based on nothing at all more than what two parties were last willing to transact for it. The stock has a ""bid"" and an ""ask"" each is the value placed by a counterparty. For the sale to occur, one party must meet the other. The stock transacts and that is the price. For a stock to ""go up"" people must be willing to pay more for it. Likewise, for it to ""go down"" people must be willing to accept less for it."
"First, what structure does your index fund have?  If it is an open-end mutual fund, there are no bid/ask spread as the structure of this security is that it is priced once a day and transactions are done with that price.  If it is an exchange-traded fund, then the question becomes how well are authorized participants taking advantage of the spread to make the fund track the index well?  This is where you have to get into the Creation and Redemption unit construct of the exchange-traded fund where there are ""in-kind"" transactions done to either create new shares of the fund or redeem out shares of the fund.  In either case, you are making some serious assumptions about the structure of the fund that don't make sense given how these are built. Index funds have lower expense ratios and are thus cheaper than other mutual funds that may take on more costs.  If you want suggested reading on this, look at the investing books of John C. Bogle who studied some of this rather extensively, in addition to being one of the first to create an index fund that became known as ""Bogle's Folly,"" where a couple of key ones would be ""Common Sense on Mutual Funds: New Imperatives for the Intelligent Investor"" and ""Bogle on Mutual Funds: New Perspectives for the Intelligent Investor."" In the case of an open-end fund, there has to be a portion of the fund in cash to handle transaction costs of running the fund as there are management fees to come from running the fund in addition to dividends from the stocks that have to be carefully re-invested and other matters that make this quite easy to note.  Vanguard 500 Index Investor portfolio(VFINX) has .38% in cash as an example here where you could look at any open-end mutual fund's portfolio and notice that there may well be some in cash as part of how the fund is managed.  It’s the Execution, Stupid would be one of a few articles that looks at the idea of ""tracking error"" or how well does an index fund actually track the index where it can be noted that in some cases, there can be a little bit of active management in the fund. Just as a minor side note, when I lived in the US I did invest in index funds and found them to be a good investment.  I'd still recommend them though I'd argue that while some want to see these as really simple investments, there can be details that make them quite interesting to my mind. How is its price set then? The price is computed by taking the sum value of all the assets of the fund minus the liabilities and divided by the number of outstanding shares.  The price of the assets would include the closing price on the stock rather than a bid or ask, similar pricing for bonds held by the fund, derivatives and cash equivalents.  Similarly, the liabilities would be costs a fund has to pay that may not have been paid yet such as management fees, brokerage costs, etc. Is it a weighted average of all the underlying stock spreads, or does   it stand on its own and stems from the usual supply & demand laws ? There isn't any spread used in determining the ""Net Asset Value"" for the fund.  The fund prices are determined after the market is closed and so a closing price can be used for stocks. The liabilities could include the costs to run the fund as part of the accounting in the fund, that most items have to come down to either being an asset, something with a positive value, or a liability, something with a negative value. Something to consider also is the size of the fund.  With over $7,000,000,000 in assets, a .01% amount is still $700,000 which is quite a large amount in some ways." Options, both puts and calls, are typically written/sold at different strike prices. For example, even though the stock of XYZ is currently trading at $12.50, there could be put options for prices ranging from $0.50 to $30.00, just as an example. There are several factors that go into determining the strike prices at which people are willing to write options. The writer/seller of an option is the person on the other side of the trade that has the opposite opinion of you. If you are interested in purchasing a put on a stock to hedge your downside, that means the writer/seller of the put is betting that you are wrong and that the stock price will rise instead. Hopefully, before you invested in this stock, you evaluated the company.  You looked at the financial information about the company and where the company was headed, and evaluated whether the stock was undervalued or overvalued.  Hopefully, you determined that the stock was undervalued at the time you bought it. The thing to do now is to reevaluate the stock.  Do you think the stock is overvalued or undervalued right now?  If you didn't own it, would you buy it today?  Instead of looking at the past performance of the stock, you want to try to determine which direction the stock will go from today.  If you wouldn't buy it today at it's current price, then you should sell. If you have no idea how to do this evaluation, neither do I.  For me, with the investing knowledge I have right now, investing in an individual stock would be way too risky.  If you don't know how to evaluate a stock and determine if it is a good buy or not, then you should stay away from individual stocks and instead invest in stock mutual funds, which lower the risk by diversifying over lots of stocks. "Note that the series you are showing is the historical spot index (what you would pay to be long the index today), not the history of the futures quotes. It's like looking at the current price of a stock or commodity (like oil) versus the futures price.  The prompt futures quote will be different that the spot quote. If you graphed the history of the prompt future you might notice the discontinuity more. How do you determine when to roll from one contract to the other? Many data providers will give you a time series for the ""prompt"" contract history, which will automatically roll to the next expiring contract for you.  Some even provide 2nd prompt, etc. time series.  If that is not available, you'd have to query multiple futures contracts and interleave them based on the expiry rules, which should be publicly available. Also is there not a price difference from the contract which is expiring and the one that is being rolled forward to? Yes, since the time to delivery is extended by ~30 days when you roll to the next contract. but yet there are no sudden price discontinuities in the charts. Well, there are, but it could be indistinguishable from the normal volatility of the time series." I was thinking that the value of the stock is the value of the stock...the actual number of shares really doesn't matter, but I'm not sure. You're correct.  Share price is meaningless.   Google is $700 per share, Apple is $100 per share, that doesn't say anything about either company and/or whether or not one is a better investment over the other. You should not evaluate an investment decision on price of a share.  Look at the books decide if the company is worth owning, then decide if it's worth owning at it's current price. Your observation is mostly right, that 1 is a the number around which this varies.  You are actually referencing PEG, P/E to Growth ratio, which is a common benchmark to use to evaluate a stock. The article I link to provides more discussion. "Say we have stock XYZ that costs $50 this second. It doesn't cost XYZ this second. The market price only reflects the last price at which the security traded. It doesn't mean that if you'll get that price when you place an order. The price you get if/when your order is filled is determined by the bid/ask spreads. Why would people sell below the current price, and not within the range of the bid/ask? Someone may be willing to sell at an ask price of $47 simply because that's the best price they think they can sell the security for. Keep in mind that the ""someone"" may be a computer that determined that $47 is a reasonable ask price. Remember that bid/ask spreads aren't fixed, and there can be multiple bid/ask prices in a market at any given time. Your buy order was filled because at the time, someone else in the market was willing to sell you the security for the same price as your bid price. Your respective buy/sell orders were matched based on their price (and volume, conditional orders, etc). These questions may be helpful to you as well: Can someone explain a stock's ""bid"" vs. ""ask"" price relative to ""current"" price? Bids and asks in case of market order Can a trade happen ""in between"" the bid and ask price? Also, you say you're a day trader. If that's so, I strongly recommend getting a better grasp on the basics of market mechanics before committing any more capital. Trading without understanding how markets work at the most fundamental levels is a recipe for disaster." "I can see two possibilities. Either a deal is struck that someone (the company itself, or a large owner) buys out the remaining shares. This is the scenario @mbhunter is talking about, so I won't go too deeply into it, but it simply means that you get money in your bank account for the shares in question the same as if you were to sell them for that price (in turn possibly triggering tax effects, etc.). I imagine that this is by far the most common approach. The other possibility is that the stock is simply de-listed from a public stock exchange, and not re-listed elsewhere. In this case, you will still have the stock, and it will represent the same thing (a portion of the company), but you will lose out on most of the ""market"" part of ""stock market"". That is, the shares will still represent a monetary value, you will have the same right to a portion of the company's profits as you do now, etc., but you will not have the benefit of the market setting a price per share so current valuation will be harder. Should you wish to buy or sell stock, you will have to find someone yourself who is interested in striking a deal with you at a price point that you feel comfortable with."