After Hours S&P 500
The futures market trades 24 hours a day, 5.5 days a week. S&P 500 futures market continues trading, and this gives pricing exposure and influences the individual stocks when they resume trading in US session. "My original answer contained a fundamental error: it turns out that it is not true that any exchange can create its own product to track any underlying index.  If the underlying index is copyrighted (such as the S&P indices, Russell indices, Dow Jones indices, etc.) then the exchange must enter into a licensing agreement (usually exclusive) with the copyright holder in order to use the index's formula (and name).  Without such a license the exchange would only be able to approximate the underlying index, and I don't think that happens very much (because how would you market such a product?). The CME offers several futures (and other derivatives) whose face value is equivalent to some multiple of the S&P500's value on the date when the product expires.  When such a product is actively traded, it may serve as a reasonable indicator of the ""market""'s expectation of the S&P500's future value. So, you could pay attention to the front month of the CME's S&P 500 Mini future, which trades from 17:00-16:00 Chicago time, Sunday night through Friday afternoon.  But remember that the prices quoted there are As another example, if you care about the Russell 2000 index, until 2017 the ICE Exchange happened to hold the license for its derivatives.  They traded from 20:00-17:30 New York time, Sunday night through Friday afternoon.  But in mid-2017 CME bought that license as well, so now you'll want to track it here. Moral: There's almost always some ""after hours"" product out there tracking whatever index you care about, but you may have to do some digging to find it, and it might not be all that useful for your specific purpose."
"Regarding SPY: ""One SPDR unit is valued at approximately 1/10 of the value of the S&P 500. Dividends are distributed quarterly, and are based on the accumulated stock dividends held in trust, less any expenses of the trust.""  (source)  These are depository receipts, not the actual stocks. Regarding IVV: ""The component stocks are weighted according to the total float-adjusted market value of their outstanding shares. The Fund invests in sectors, such as energy, information technology, industrials, financials, consumer staples, healthcare, telecom services, consumer discretionary and materials.""  (more here) VOO is the Vanguard S&P 500 ETF. The tracking error seems pretty small to me.  I went to Google Finance and plotted the percent change for all four on one chart.  They lie pretty much on top of one another.  The actual dollar value of each one doesn't matter nearly as much as the fact that they move up and down almost in lock-step.  There may be a larger difference going farther out, but for three separate financial products, the agreement is still remarkably good." You asked some direct questions, here are some direct answers: 10% of your salary is a popular rule of thumb. An IRA account is something to consider, you can open one with any of the major discount brokers and select an S&P 500 index fund for your investment. You can let it sit. That's the beauty of an index fund, it simply matches the market and you don't have to worry about trying to beat the market because you ARE the market! The average annual return for the S&P 500 Index has been around 10% (since inception). That's no guarantee, and some years are more or less and up or down. Over the long run, it goes up. "They do but you're missing some calculations needed to gain an understanding. Intro To Stock Index Weighting Methods notes in part: Market cap is the most common weighting method used by an index.   Market cap or market capitalization is the standard way to measure the   size of the company. You might have heard of large, mid, or small cap   stocks? Large cap stocks carry a higher weighting in this index. And   most of the major indices, like the S&P 500, use the market cap   weighting method. Stocks are weighted by the proportion of their market cap to the total   market cap of all the stocks in the index. As a stock’s price and   market cap rises, it gains a bigger weighting in the index. In turn   the opposite, lower stock price and market cap, pushes its weighting   down in the index.  Pros Proponents argue that large companies have a bigger effect on the   economy and are more widely owned. So they should have a bigger   representation when measuring the performance of the market. Which is   true. Cons It doesn’t make sense as an investment strategy. According to a market   cap weighted index, investors would buy more of a stock as its price   rises and sell the stock as the price falls. This is the exact   opposite of the buy low, sell high mentality investors should use. Eventually, you would have more money in overpriced stocks and less in   underpriced stocks. Yet most index funds follow this weighting method. Thus, there was likely a point in time where the S & P 500's initial sum was equated to a specific value though this is the part you may be missing here. Also, how do you handle when constituents change over time? For example, suppose in the S & P 500 that a $100,000,000 company is taken out and replaced with a $10,000,000,000 company that shouldn't suddenly make the index jump by a bunch of points because the underlying security was swapped or would you be cool with there being jumps when companies change or shares outstanding are rebalanced? Consider carefully how you answer that question. In terms of histories, Dow Jones Industrial Average and S & P 500 Index would be covered on Wikipedia where from the latter link: The ""Composite Index"",[13] as the S&P 500 was first called when it   introduced its first stock index in 1923, began tracking a small   number of stocks. Three years later in 1926, the Composite Index   expanded to 90 stocks and then in 1957 it expanded to its current   500.[13] Standard & Poor's, a company that doles out financial information and analysis, was founded in 1860 by Henry Varnum Poor. In   1941 Poor's Publishing (Henry Varnum Poor's original company) merged   with Standard Statistics (founded in 1906 as the Standard Statistics   Bureau) and therein assumed the name Standard and Poor's Corporation.   The S&P 500 index in its present form began on March 4, 1957.   Technology has allowed the index to be calculated and disseminated in   real time. The S&P 500 is widely used as a measure of the general   level of stock prices, as it includes both growth stocks and value   stocks. In September 1962, Ultronic Systems Corp. entered into an agreement   with Standard and Poor's. Under the terms of this agreement, Ultronics   computed the S&P 500 Stock Composite Index, the 425 Stock Industrial   Index, the 50 Stock Utility Index, and the 25 Stock Rail Index.   Throughout the market day these statistics were furnished to Standard   & Poor's. In addition, Ultronics also computed and reported the 94 S&P   sub-indexes.[14] There are also articles like Business Insider that have this graphic that may be interesting: S & P changes over the years The makeup of the S&P 500 is constantly changing notes in part: ""In most years 25 to 30 stocks in the S&P 500 are replaced,"" said   David Blitzer, S&P's Chairman of the Index Committee. And while there   are strict guidelines for what companies are added, the final decision   and timing of that decision depends on what's going through the heads   of a handful of people employed by Dow Jones." You can check the website for the company that manages the fund. For example, take the iShares Nasdaq Biotechnology ETF (IBB). iShares publishes the complete list of the fund's holdings on their website. This information isn't always easy to find or available, but it's a place to start. For some index funds, you should just be able to look up the index the fund is trying to match. This won't be perfect (take Vanguard's S&P 500 ETF (VOO); the fund holds 503 stocks, while the S&P 500 index is comprised of exactly 500), but once again, it's a place to start. A few more points to keep in mind. Remember that many ETF's, including equity ETF's, will hold a small portion of their assets in cash or cash-equivalent instruments to assist with rebalancing. For index funds, this may not be reflected in the index itself, and it may not show up in the list of holdings. VOO is an example of this. However, that information is usually available in the fund's prospectus or the fund's site. Also, I doubt that many stock ETF's, at least index funds, change their asset allocations all that frequently. The amounts may change slightly, but depending on the size of their holdings in a given stock, it's unlikely that the fund's manager would drop it entirely. "The S&P 500 is an index. This refers to a specific collection of securities which is held in perfect proportion. The dollar value of an index is scaled arbitrarily and is based off of an arbitrary starting price. (Side note: this is why an index never has a ""split""). Lets look at what assumptions are included in the pricing of an index: All securities are held in perfect proportion. This means that if you invest $100 in the index you will receive 0.2746 shares of IBM, 0.000478 shares of General Motors, etc. Also, if a security is added/dropped from the list, you are immediately rebalancing the remaining money. Zero commissions are charged. When the index is calculated, they are using the current price (last trade) of the underlying securities, they are not actually purchasing them. Therefore it assumes that securities may be purchased without commission or other liquidity costs. Also closely related is the following. The current price has full liquidity. If the last quoted price is $20 for a security, the index assumes that you can purchase an arbitrary amount of the security at that price with a counterparty that is willing to trade. Dividends are distributed immediately. If you own 500 equities, and most distributed dividends quarterly, this means you will receive on average 4 dividends per day. Management is free. All equities can be purchased with zero research and administrative costs. There is no gains tax. Trading required by the assumptions above would change your holdings constantly and you are exempt from short-term or long-term capital gains taxes. Each one of these assumptions is, of course, invalid. And the fund which endeavors to track the index must make several decisions in how to closely track the index while avoiding the problems (costs) caused by the assumptions. These are shortcuts or ""approximations"". Each shortcut leads to performance which does not exactly match the index. Management fees. Fees are charged to the investor as load, annual fees and/or redemptions. Securities are purchased at real prices. If Facebook were removed from the S&P 500 overnight tonight, the fund would sell its shares at the price buyers are bidding the next market day at 09:30. This could be significantly different than the price today, which the index records. Securities are purchased in blocks. Rather than buying 0.000478 shares of General Motors each time someone invests a dollar, they wait for a few people and then buy a full share or a round lot. Securities are substituted. With lots of analysis, it may be determined that two stocks move in tandem. The fund may purchase two shares of General Motors rather than one of General Motors and Ford. This halves transaction costs. Debt is used. As part of substitution, equities may be replaced by options. Option pricing shows that ownership of options is equivalent to holding an amount of debt. Other forms of leverage may also be employed to achieve desired market exposure. See also: beta.  Dividends are bundled. VFINX, the largest S&P 500 tracking fund, pays dividends quarterly rather than immediately as earned. The dividend money which is not paid to you is either deployed to buy other securities or put into a sinking fund for payment. There are many reasons why you can't get the actual performance quoted in an index. And for other more exotic indices, like VIX the volatility index, even more so. The best you can do is work with someone that has a good reputation and measure their performance." No, it is just normal sideways action.  Think of this week kind of like October 14th - October 20th. It is a day traders week. If you're not day trading then either do after hours trading at the second of the news, or buy/sell on thursday (i'm bullish).  This is normal market activity. I wouldn't consider it out of the ordinary. When there is sideways action there is always good times to both buy and sell, if you realize it. For example, today is the perfect day to buy ... maybe when $SPX is 1240-1244. "EDIT: It was System Disruption or Malfunctions August 24, 2015 2:12 PM EDT   Pursuant to Rule 11890(b) NASDAQ, on its own motion, in conjunction   with BATS, and FINRA has determined to cancel all trades in security   Blackrock Capital Investment. (Nasdaq: BKCC) at or below $5.86 that   were executed in NASDAQ between 09:38:00 and 09:46:00 ET. This   decision cannot be appealed. NASDAQ will be canceling trades on the   participants behalf. A person on Reddit claimed that he was the buyer. He used Robinhood, a $0 commission broker and start-up.  The canceled trades are reflected on CTA/UTP and the current charts will differ from the one posted below.  It is an undesired effect of the 5-minute Trading Halt.  It is not ""within 1 hour of opening, BKCC traded between $0.97 and $9.5"".  Those trades only occurred for a few seconds on two occasions.  One possible reason is that when the trading halt ended, there was a lot of Market Order to sell accumulated.  Refer to the following chart, where each candle represents a 10 second period. As you can see, the low prices did not ""sustain"" for hours.   And the published halts." "I read the book, and I'm willing to believe you'd have a good chance of beating the market with this strategy - it is a reasonable, rational, and mechanical investment discipline. I doubt it's overplayed and overused to the point that it won't ever work again. But only IF you stick to it, and doing so would be very hard (behaviorally). Which is probably why it isn't overplayed and overused already. This strategy makes you place trades in companies you often won't have heard of, with volatile prices. The best way to use the strategy would be to try to get it automated somehow and avoid looking at the individual stocks, I bet, to take your behavior out of it. There may well be some risk factors in this strategy that you don't have in an S&P 500 fund, and those could explain some of the higher returns; for example, a basket of sketchier companies could be more vulnerable to economic events. The strategy won't beat the market every year, either, so that can test your behavior. Strategies tend to work and then stop working (as the book even mentions). This is related to  whether other investors are piling in to the strategy and pushing up prices, in part.  But also, outside events can just happen to line up poorly for a given strategy; for example a bunch of the ""fundamental index"" ETFs that looked at dividend yield launched right before all the high-dividend financials cratered. Investing in high-dividend stocks probably is and was a reasonable strategy in general, but it wasn't a great strategy for a couple years there. Anytime you don't buy the whole market, you risk both positive and negative deviations from it. Here's maybe a bigger-picture point, though. I happen to think ""beating the market"" is a big old distraction for individual investors; what you really want is predictable, adequate returns, who cares if the market returns 20% as long as your returns are adequate, and who cares if you beat the market by 5% if the market cratered 40%. So I'm not a huge fan of investment books that are structured around the topic of beating the market. Whether it's index fund advocates saying ""you can't beat the market so buy the index"" or Greenblatt saying ""here's how to beat the market with this strategy,"" it's still all about beating the market. And to me, beating the market is just irrelevant. Nobody ever bought their food in retirement because they did or did not beat the market. To me, beating the market is a game for the kind of actively-managed mutual fund that has a 90%-plus R-squared correlation with the index; often called an ""index hugger,"" these funds are just trying to eke out a little bit better result than the market, and often get a little bit worse result, and overall are a lot of effort with no purpose. Just get the index fund rather than these. If you're getting active management involved, I'd rather see a big deviation from the index, and I'd like that deviation to be related to risk control: hedging, or pulling back to cash when valuations get rich, or avoiding companies without a ""moat"" and margin of safety, or whatever kind of risk control, but something. In a fund like this, you aren't trying to beat the market, you're trying to increase the chances of adequate returns - you're optimizing for predictability. I'm not sure the magic formula is the best way to do that, focused as it is on beating the market rather than on risk control. Sorry for the extra digression but I hope I answered the question a bit, too. ;-)"