Is it a good idea to put everything in the S&P500?
At a very high-level, the answer is yes, that's a good idea. For money that you want to invest on the scale of decades, putting money into a broad, market-based fund has historically given the best returns. Something like the Vanguard S&P 500 automatically gives you a diverse portfolio, with super low expenses. As it sounds like you understand, the near-term returns are volatile, and if you really think you might want this money in the next few years, then the stock market might not be the best choice. As a final note, as one of the comments mentioned, it makes sense to hold a broad, market-based fund for your IRA as well, if possible. What you choose to invest in depends largely on your own goals and time horizon.  You state that your time horizon is a few decades. Most studies have shown that the equity market as a whole has outperformed most other asset types (except perhaps property in some cases) over the long term.  The reason that time horizon is important is that equities are quite volatile. Who knows whether your value will halve in the next year? But we hope that over the longer term, things come out in the wash, and tomorrow's market crash will recover, etc.  However, you must realize that if your goals change, and you suddenly need your money after 2 years, it might be worth less in two years than you expect.
"Index funds are well-known to give the best long-term investment. Not exactly. Indexes give the best long term performance when compared to actively managing investments directly in the underlying stocks. That is, if you compare an S&P500 index to trying to pick stocks that are part of it, you're more likely to succeed with blindly following the index than trying to actively beat it. That said, no-one promises that investing in S&P500 is better than investing in DJIA, for example. These are two different indexes tracking different stocks and areas. So when advisers say ""diversify"" they don't mean it that you should diversify between different stocks that build up the S&P500 index. They mean that you should diversify your investments in different areas. Some in S&P500, some in DJIA, some in international indexes, some in bond indexes, etc. Still, investing in various indexes will likely yield better results than actively managing the investments trying to beat those indexes, but you should not invest in only one, and that is the meaning of diversification. In the comments you asked ""why diversify at all?"", and that is entirely a different question from your original ""what diversification is?"". You diversify to reduce the risk of loss from one side, and widen the net for gains from another. The thing is that any single investment can eventually fail, regardless of how it performed before. You can see that the S&P500 index lost 50% of its value twice within ten years, whereas before it was doubling itself every several years. Many people who were only invested in that index (or what's underlying to it) lost a lot of money. But consider you've diversified, and in the last 20 years you've invested in a blend of indexes that include the S&P500, but also other investments like S&P BSE SENSEX mentioned by Victor below. You would reduce your risk of loss on the American market by increasing your gains on the Indian market. Add to the mix soaring Chinese Real Estate market during the time of the collapse of the US real-estate, gains on the dollar losing its value by investing in other currencies (Canadian dollar, for example), etc. There are many risks, and by diversifying you mitigate them, and also have a chance to create other potential gains. Now, another question is why invest in indexes. That has been answered before on this site. It is my opinion that some methods of investing are just gambling by trying to catch the wave and they will almost always fail, and rarely will individual stock picking beat the market. Of course, after the fact its easy to be smart and pick the winning stocks. But the problem is to be able to predict those charts ahead of time." You can employ a hedging strategy using short selling, put options, or other methods that will partially neutralize your exposure to the overall market.   e.g. You could short sell a market-wide index such as the S&P500, while going long (buying) the company you are interested in. Investopedia has a nice primer on this: Also, see this related question here: At your age, I don't think its a bad idea to invest entirely in stocks. The concern with stocks is their volatility, and at 40+ years from retirement, volatility does not concern you. Just remember that if you ever want to call upon your 401(k) for anything other than retirement, such as a down payment on a home (which is a qualified distribution that is not subject to early distribution penalties), then you should reconsider your retirement allocations. I would not invest 100% into stocks if I knew I were going to buy a house in five years and needed that money for a down payment. If your truly saving strictly for a retirement that could occur forty years in the future, first good for you, and second, put it all in an index fund. An S&P index has a ridiculously low expense ratio, and with so many years away from retirement, it gives you an immense amount of flexibility to choose what to do with those funds as your retirement date approaches closer every year. "I hope I'm misunderstanding your plan... you want to invest in a way that will make SO MUCH that you pay back all of the loan payments with investment gains? Like the answer I gave on the preceding question, and like @littleadv's comment/mhoran's answers... don't do this. No good will come of it.  This strategy requires higher returns, but does not necessarily give you a better return.   But because you asked the question again, let me specify what you're missing... I do think that learning is a good thing. It boils down to two very significant problems that you haven't addressed:  (1) Where are you getting your monthly ""income"" from?  (2) Realistic vs. Daydreaming--How big do any gains have to be and does that exist in the real world in a way that you can capture?  In a nutshell, if my answer to the last question showed that it's crazy to invest and pay back out of your capital and income... since you're trying to keep your capital and only pay back with monthly gains, this one will require even higher and thus more unrealistic gains.  The model you're implying:  If that's what you mean with this model, (which I think you do), then here are my two very key questions again: How are you getting your monthly income? Financial investments (i.e. stocks or bonds) will have two components of value. One component of value is the stream of payments, such as a monthly dividend from stocks that pay those, or the interest payment from a bond. The other is the ability to resell a security to another investor, receiving back your capital.  So... you either have to find Bonds//Dividend stocks that pay >52% returns tax-free each year, and pay this loan off with the payments. (Or higher returns to cover taxes, but these kinds of investments do not exist for you.)  OR you can try to invest in something, pray that it goes up ≥4.323% per month and so that you can sell it, pay back your loan payment with the proceeds, and use the capital to buy your next investment... that will go up 4.323% per month, to turn and sell it again.  The pros that do model this type of speculation go into much more depth than you are capable of. They build models that incorporate probabilities for rates of return based on historical data. They have better information, and have specialized in calculating this all out. They even have access to better investment opportunities (like pre-IPO Twitter or private notes). You just won't find the opportunities to make this happen, each month, for 24 months. (Again, you won't find them. They do not exist for you in as an investor in securities) Realistic vs. Daydreaming So... clearly I hope that by now I have convinced you that these would be the required returns. They simply aren't available to you. If they were, you would still run into obstacles with converting 'book' returns into physical money that you could repay the loans with, and then continuing that growth.  And while I appreciate the notion that 'if I could just make the payments each month, I'd have $10,000 after 24 months!' I guarantee you that you'll be better off finding another way to target that same investment.  Along the lines of what mhoran said, if you aim for a basic 401K or other similar investment account and target it into the S&P500, you might see returns of anywhere from -25% to +25% over the next 24 months... but if things went like they tend to average for the S&P500, it's more like ~7% annually. Check out a ""savings target calculator"" like this one from Bankrate.com and put in the numbers... if you can save about $390 a month you'll be at $10K in 24 months. It's not as fun as the other, but you can actually expect to achieve that.  You will not find consistent >50% returns on your money annually." One reason it matters whether or not you're beating the S&P 500 (or the Wilshire 5000, or whatever benchmark you choose to use) is to determine whether or not you'd be better off investing in an index fund (or some other investment vehicle) instead of pursuing whatever your current investment strategy happens to be.  Even if your investment strategy makes money, earning what the S&P 500 has averaged over multiple decades (around 10%) with an index fund means a lot more money than a 5% return with an actively managed portfolio (especially when you consider factors like compound interest and inflation). I use the S&P 500 as one of my criteria for judging how well (or poorly) my financial adviser is doing for me. If his recommendations (or trading activity on my behalf, if authorized) are inferior to the S&P 500, for too long, then I have a basis to discontinue the relationship. Check out this Wikipedia entry on stock market indices. There are legitimate criticisms, but on the whole I think they are useful. As an aside, the reason I point to index funds specifically is that they are the one of the lowest-cost, fire-and-forget investment strategies around.  If you compare the return of the S&P 500 index over multiple decades with most actively managed mutual funds, the S&P 500 index comes out ahead. "Here is, from Yahoo Finance, the S&P 500 over the last ~60 years (logarithmic scale):  The behavior since ~2000 has been weird, by historical standards. And it's very easy, looking at that graph, to say ""yes! I would have made so much money had I invested in March '09!"". Of course, back in March '09, it wasn't so clear that was the bottom. But, yes, over the last 10 years or so, you could have made more money by adopting a rule that you'll accumulate cash in a FDIC (or similar) insured savings account, and dump it into an S&P index fund/ETF when the index is n% off its high. Of course, if you look at the rest of the chart, that strategy looks a lot less promising. Start in the early 80's, and you'd have held cash until the crash in 2000. Except for the recent weirdness, the general trend in the S&P 500 (and stock markets in general) has been upward. In other words, to a first-order approximation, the S&P 500 is always at an all-time high. That's just the general trend." "My gut is to say that any time there seems to be easy money to be made, the opportunity would fade as everyone jumped on it. Let me ask you - why do you think these stocks are priced to yield 7-9%? The DVY yields 3.41% as of Aug 30,'12.  The high yielding stocks you discovered may very well be hidden gems. Or they may need to reduce their dividends and subsequently drop in price.  No, it's not 'safe.' If the stocks you choose drop by 20%, you'd lose 40% of your money, if you made the purchase on 50% margin. There's risk with any stock purchase, one can claim no stock is safe. Either way, your proposal juices the effect to creating twice the risk.  Edit - After the conversation with Victor, let me add these thoughts. The ""Risk-Free"" rate is generally defined to be the 1yr tbill (and of course the risk of Gov default is not zero). There's the S&P 500 index which has a beta of 1 and is generally viewed as a decent index for comparison. You propose to use margin, so your risk, if done with an S&P index is twice that of the 1X S&P investor. However, you won't buy S&P but stocks with such a high yield I question their safety. You don't mention the stocks, so I can't quantify my answer, but it's tbill, S&P, 2X S&P, then you." "General advice is to keep 6 months worth of income liquid -- in your case, you might want to leave 1 year liquid since, even though your income is stable now, it is not static (i.e., you're not drawing salary from an employer).   The rest of it?  If you don't plan on using it for any big purchases in the next 5 or so years, invest it.  If you don't, you will probably lose money in the long term due to inflation (how's that for a risk? :).  There are plenty of options for the risk averse, many of which handily beat inflation, though without knowing your country of residence, it's hard to say.  In all likelihood, though, you'll want to invest in index funds -- such as ETFs -- that basically track industries, rather than individual companies.  This is basically free portfolio diversity -- they lose money only when an entire sector loses value.  Though even with funds of this type, you still want to ensure you purchase multiple different funds that track different industries.  Don't just toss all of your funds into an IT index, for example.   Before buying, just look at the history of the fund and make sure it has had a general upward trajectory since 2008 (I've bought a few ETFs that remained static...not what we're looking for in an investment!).  If the brokerage account you choose doesn't offer commission free trades on any of the funds you want (personally, I use Schwab and their ETF portfolio), try to ""buy in bulk.""  That way you're not spending so much on trades.   There are other considerations (many indexed funds have high management costs, but if you go with ETFs, they don't, and there's the question of dividends, etc), but that is getting into the weeds as far as investing knowledge is concerned.   Beyond that, just keep in mind it'll take 1-2 weeks for you to see that money if you need it, and there's obviously no guarantee it'll be there if you do need it for an emergency."