Data source for historical intra-day bid/ask price data for stocks?
FreeStockCharts.com keeps some intra-day trading history.  You have to create an account to look up individual stocks.  Once you create a free account you can get intra-day trading history for the last month (Hourly for past month, 15 minutes for past week, 1 minute for past day).  Going back past one month and it only keeps daily close history. Here is Family Dollary's (FDO) hourly intra-day chart for the past month: Interactive Brokers provides historical intraday data including Bid, Ask, Last Trade and Volume for the majority of stocks. You can chart the data, download it to Excel or use it in your own application through their API.  EDIT: Compared to other solutions (like FreeStockCharts.com for instance), Interactive Brokers provides not only historic intraday LAST**** trades **but also historic BID and ASK data, which is very useful information if you want to design your own trading system.  I have enclosed a screenshot to the chart parameter window and a link to the API description. Check the answers to this Stackoverflow question https://stackoverflow.com/questions/754593/source-of-historical-stock-data a number of potential sources are listed This amazing site will answer all your data questions. You will need some patience and willingness to spend to get the data that you want. A lot of data is available for free too` https://www.quandl.com/
"Yes. There are several downsides to this strategy: You aren't taking into account commissions. If you pay $5 each time you buy or sell a stock, you may greatly reduce or even eliminate any possible gains you would make from trading such small amounts. This next point sounds obvious, but remember that you pay a commission on every trade regardless of profit, so every trade you make that you make at a loss also costs you commissions. Even if you make trades that are profitable more often than not, if you make quite a few trades with small amounts like this, your commissions may eat away all of your profits. Commissions represent a fixed cost, so their effect on your gains decreases proportionally with the amount of money you place at risk in each trade. Since you're in the US, you're required to follow the SEC rules on pattern day trading. From that link, ""FINRA rules define a “pattern day trader” as any customer who executes four or more “day trades” within five business days, provided that the number of day trades represents more than six percent of the customer’s total trades in the margin account for that same five business day period."" If you trip this rule, you'll be required to maintain $25,000 in a margin brokerage account. If you can't maintain the balance, your account will be locked. Don't forget about capital gains taxes. Since you're holding these securities for less than a year, your gains will be taxed at your ordinary income tax rates. You can deduct your capital losses too (assuming you don't repurchase the same security within 30 days, because in that case, the wash sale rule prevents you from deducting the loss), but it's important to think about gains and losses in real terms, not nominal terms. The story is different if you make these trades in a tax-sheltered account like an IRA, but the other problems still apply. You're implicitly assuming that the stock's prices are skewed in the positive direction. Remember that you have limit orders placed at the upper and lower bounds of the range, so if the stock price decreases before it increases, your limit order at the lower bound will be triggered and you'll trade at a loss. If you're hoping to make a profit through buying low and selling high, you want a stock that hits its upper bound before hitting the lower bound the majority of the time. Unless you have data analysis (not just your intuition or a pattern you've talked yourself into from looking at a chart) to back this up, you're essentially gambling that more often than not, the stock price will increase before it decreases. It's dangerous to use any strategy that you haven't backtested extensively. Find several months or years of historical data, either intra-day or daily data, depending on the time frame you're using to trade, and simulate your strategy exactly. This helps you determine the potential profitability of your strategy, and it also forces you to decide on a plan for precisely when you want to invest. Do you invest as soon as the stock trades in a range (which algorithms can determine far better than intuition)? It also helps you figure out how to manage your risk and how much loss you're willing to accept. For risk management, using limit orders is a start, but see my point above about positively skewed prices. Limit orders aren't enough. In general, if an active investment strategy seems like a ""no-brainer"" or too good to be true, it's probably not viable. In general, as a retail investor, it's foolish to assume that no one else has thought of your simple active strategy to make easy money. I can promise you that someone has thought of it. Trading firms have quantitative researchers that are paid to think of and implement trading strategies all the time.  If it's viable at any scale, they'll probably already have utilized it and arbitraged away the potential for small traders to make significant gains. Trust me, you're not the first person who thought of using limit orders to make ""easy money"" off volatile stocks. The fact that you're asking here and doing research before implementing this strategy, however, means that you're on the right track. It's always wise to research a strategy extensively before deploying it in the wild. To answer the question in your title, since it could be interpreted a little differently than the body of the question: No, there's nothing wrong with investing in volatile stocks, indexes, etc. I certainly do, and I'm sure many others on this site do as well. It's not the investing that gets you into trouble and costs you a lot of money; it's the rapid buying and selling and attempting to time the market that proves costly, which is what you're doing when you implicitly bet that the distribution of the stock's prices is positively skewed. To address the commission fee problem, assuming a fee of $8 per trade ... and a minimum of $100 profit per sale Commissions aren't your only problem, and counting on $100 profit per sale is a significant assumption. Look at point #4 above. Through your use of limit orders, you're making the implicit assumption that, more often than not, the price will trigger your upper limit order before your lower limit order. Here's a simple example; let's assume you have limit orders placed at +2 and -2 of your purchase price, and that triggering the limit order at +2 earns you $100 profit, while triggering the limit order at -2 incurs a loss of $100. Assume your commission is $5 on each trade.  If your upper limit order is triggered, you earn a profit of 100 - 10 = 90, then set up the same set of limit orders again. If your lower limit order is triggered this time, you incur a loss of 100 + 10 = 110, so your net gain is 90 - 110 = -20. This is a perfect example of why, when taking into account transaction costs, even strategies that at first glance seem profitable mathematically can actually fail.  If you set up the same situation again and incur a loss again (100 + 10 = 110), you're now down -20 - 110 = -130. To make a profit, you need to make two profitable trades, without incurring further losses.  This is why point #4 is so important. Whenever you trade, it's critical to completely understand the risk you're taking and the bet you're actually making, not just the bet you think you're making. Also, according to my ""algorithm"" a sale only takes place once the stock rises by 1 or 2 points; otherwise the stock is held until it does. Does this mean you've removed the lower limit order? If yes, then you expose yourself to downside risk. What if the stock has traded within a range, then suddenly starts declining because of bad earnings reports or systemic risks (to name a few)? If you haven't removed the lower limit order, then point #4 still stands.  However, I never specified that the trades have to be done within the same day.  Let the investor open up 5 brokerage accounts at 5 different firms (for safeguarding against being labeled a ""Pattern Day Trader""). Each account may only hold 1 security at any time, for the span of 1 business week. How do you control how long the security is held? You're using limit orders, which will be triggered when the stock price hits a certain level, regardless of when that happens. Maybe that will happen within a week, or maybe it will happen within the same day. Once again, the bet you're actually making is different from the bet you think you're making. Can you provide some algorithms or methods that do work for generating some extra cash on the side, aside from purchasing S&P 500 type index funds and waiting? When I purchase index funds, it's not to generate extra liquid cash on the side. I don't invest nearly enough to be able to purchase an index fund and earn substantial dividends. I don't want to get into any specific strategies because I'm not in the business of making investment recommendations, and I don't want to start. Furthermore, I don't think explicit investment recommendations are welcome here (unless it's describing why something is a bad idea), and I agree with that policy. I will make a couple of points, however. Understand your goals. Are you investing for retirement or a shorter horizon, e.g. some side income? You seem to know this already, but I include it for future readers.  If a strategy seems too good to be true, it probably is. Educate yourself before designing a strategy. Research fundamental analysis, different types of orders (e.g., so you fully understand that you don't have control over when limit orders are executed), different sectors of the market if that's where your interests lie, etc. Personally, I find some sectors fascinating, so researching them thoroughly allows me to make informed investment decisions as well as learn about something that interests me. Understand your limits. How much money are you willing to risk and possibly lose? Do you have a risk management strategy in place to prevent unexpected losses? What are the costs of the risk management itself? Backtest, backtest, backtest. Ideally your backtesting and simulating should be identical to actual market conditions and incorporate all transaction costs and a wide range of historical data. Get other opinions. Evaluate those opinions with the same critical eye as I and others have evaluated your proposed strategy." "The prices quoted are for currency pairs traded on the foreign exchange market. For currencies traded on these exchanges, the exchange rates of a given currency pair are determined by the market, so supply and demand, investor confidence, etc. all play a role. EBS and Reuters are the two primary trading platforms in the foreign exchange market, and much of the data on exchange rates comes from them. Websites will usually get their data either from these sources directly or from a data provider that in turn gets it from EBS, Reuters, or another data source like Bloomberg or Haver Analytics. These data sources aren't free, however.  In the US, many contracts, transactions, etc. that involve exchange rates use the exchange rate data published by the Federal Reserve. You might see this in contracts that specify to use ""the exchange rate published by the Federal Reserve at 12 pm (noon) on date --some date--"". You can also look at the Federal Reserve Economic Data, which maintains data series of historical daily, weekly, and monthly exchange rates for major currency pairs. These data are free, although they aren't realtime. Data for each business day is mostly updated the next business day." This is just a shot in the dark but it could be intermarket data. If the stock is interlisted and traded on another market exchange that day then the Yahoo Finance data feed might have picked up the data from another market. You'd have to ask Yahoo to explain and they'd have to check their data. 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. A couple ways, but its not a guarantee.  You have to have special charts. Instead of each tick being 1 min, 5 min, or whatever, it is a set number of trades. Say 2000. Since retail investors only buy and sell in small amounts, there will be small volume per tick. An institutional investor, however, would have a much much higher trade lot size, even if using an algo. Thus, large volume spikes in such a chart would signal institutional activity over retail. Similarly, daily charts showing average trade size can help you pick out when institutional activity is highest, as they have much larger trade sizes. You could also learn how the algos work and look for evidence one is being used. ie every time price hits VWAP a large sell order goes through would indicate an institutional investor is selling, especially if it happens multiple times in a row. Good day! Did a little research by using oldest public company (Dutch East India Company, VOC, traded in Amsterdam Stock Exchange) as search criteria and found this lovely graph from http://www.businessinsider.com/rise-and-fall-of-united-east-india-2013-11?IR=T :  Why it is relevant? Below the image I found the source of data - Global Financial Data. I guess the answer to your question would be to go there: https://www.globalfinancialdata.com/index.html  Hope this helps and good luck in your search! Like others have said, mutual funds don't have an intraday NAV, but their ETF equivalents do. Use something like Yahoo Finance and search for the ETF.IV. For example VOO.IV. This will give you not the ETF price (which may be at a premium or discount), but the value of the underlying securities updated every 15 seconds. I know of no free source for 10 years historical data on a large set of companies.  Now, if it's just a single company or small number that interest you, contact Investor Relations at the company(ies) in question; they may be willing to send you the data for free.