Rate of return of stock index
The return from one day to the next is based on the Day's closing price.  To be clear - opening prices can be quite different from the prior day close. In your example, they are pretty close, but this is not always the case. Just pull a larger data set to observe this.  The above aside, dividends are not reflected in the index, so, after a dividend has occurred, you'd need to account for this if you are looking for true total return. In 2011, the S&P closed at 1257.60 vs a 2010 year end 1257.64. The return, however was 2.11%, not zero, after accounting for the dividends. To me, articles that suggest the yearly return was zero are inaccurate and misleading.
To figure this out, you need to know the price per share then vs the price per share now.  Google Finance will show you historical prices.  For GOOG, the closing price on January 5, 2015 was $513.87.  The price on December 31, 2015 was $758.88.  Return on Investment (ROI) is calculated with this formula: ROI = (Proceeds from Investment - Cost of Investment) / Cost of Investment Using this formula, your return on investment would be 47.7%.  Since the time period was one year, this number is already an annualized return.  If the time period was different than one year, you would normally convert it to an annualized rate of return in order to compare it to other investments. "He is wrong.  Using Total Return (Reinvesting Dividend), from the peak in December 1999, it only took 6 years to recover.   You can check the data for free here. Make sure you choose ""Gross Index Level"".  ACWI Index is Developed Markets + Emerging Markets.  World Index is Developed Markets only." Yes an index is by definition any arbitrary selection. In general, to measure performance there are 2 ways: By absolute return - meaning you want a positive return at all times ie. 10% is good. -1% is bad. By relative return - this means beating the benchmark. For example, if the benchmark returns -20% and your portfolio returns -10%, then it has delivered +10% relative returns as compared to the benchmark. You've got the right idea, except that the stated interest rate is normalized for a 1-year investment.  Hence if you buy a 4-week bill, you're getting something closer to 4/52 of what you've computed in your question.  More precisely, the Treasury uses a 360 day year for these calculations, so you multiply the stated rate by (number of days until maturity)/360 to get the actual rate of return. "The author is using an approximation to what you have exactly, which is called a ""true"" time-weighted rate of return. You have expressed the total time-weighted return for the period in question.  In order to express this as an annual rate, you may annualize it by adding one, raising to the 1/y power, and subtracting one again, for a period of y years. The alternative to a time-weighted return is a money-weighted return, which is actually another name for the internal rate of return." "Good observation. In fact, the S&P index itself is guilty of not including dividends. So when you look at the index alone, the delta between any two points in time diverges, and the 20 return observed if one fails to include dividends is meaningless, in my my humble opinion. Yahoo finance will let you look at a stock ticker and offer you an ""adjusted close"" to include the dividend effect." This doesn't really make sense, as the small cap indices have a similar rate of growth as the s&amp;p 500. The global scale has some relevance, but exports are included in GDP as well, so it's not the full story.  A better answer, as is noted in comments lower down, is that the S&amp;P does not **grow** at 6%. It *returns* 6% per year. The dividend yield of the s&amp;p is a bit over 2%. Dividends are not growth, they are simply income; they may also grow themselves, but rarely by 6% per year (in real terms). Additional income that's not paid out in dividends probably amounts to another 1-2%. Growth is the final 1-3%, which makes it roughly match GDP. If you mean the internal rate of return, then the quarterly rate of return which would make the net present value of these cash flows to be zero is 8.0535% (found by goal seek in Excel), or an equivalent compound annual rate of 36.3186% p.a. The net present value of the cash flows is: 10,000 + 4,000/(1+r) - 2,000/(1+r)^2 - 15,125/(1+r)^3, where r is the quarterly rate. If instead you mean Modified Dietz return, then the net gain over the period is: End value - start value - net flow = 15,125 - 10,000 - (4,000 - 2,000) = 3,125 The weighted average capital invested over the period is: 1 x 10,000 + 2/3 x 4,000 - 1/3 x 2,000 = 12,000 so the Modified Dietz return is 3,125 / 12,000 = 26.0417%, or 1.260417^(1/3)-1 = 8.0201% per quarter, or an equivalent compound annual rate of 1.260417^(4/3)-1 = 36.1504%. You are using an inappropriate formula, because we know for a fact that the flows take place at the beginning/end of the period. Instead, you should be combining the returns for the quarters (which have in fact been provided in the question). To calculate this, first calculate the growth factor over each quarter, then  link them geometrically to get the overall growth factor. Subtracting 1 gives you the overall return for the 3-quarter period. Then convert the result to a quarterly rate of return. Growth factor in 2012 Q4 is 11,000/10,000 = 1.1 Growth factor in 2013 Q1 is 15,750/15,000 = 1.05 Growth factor in 2013 Q2 is 15,125/13,750 = 1.1 Overall growth factor is 1.1 x 1.05 x 1.1 = 1.2705 Return for the whole period is 27.05% Quarterly rate of return is 1.2705^(1/3)-1 = 8.3074% Equivalent annual rate of return is 1.2705^(4/3)-1 = 37.6046% ========= I'd recommend you to refer to Wikipedia. Yes - it's called the rate of inflation. The rate of return over the rate of inflation is called the real rate of return.   So if a currency experiences a 2% rate of inflation, and your investment makes a 3% rate of return, your real rate of return is only 1%. One problem is that inflation is always backwards-looking, while investment returns are always forward-looking. There are ways to calculate an expected rate of inflation from foreign exchange futures and other market instruments, though. That said, when comparing investments, typically all investments are in the same currency, so the effect of inflation is the same, and inflation makes  no difference in a comparative analysis.  When comparing investments in different currencies, then the rate of inflation may become important. That is true. You will not be able to reconstruct the value of the index from the data returned with this script.  I initially wrote this script because I wanted data for a lot of stocks and I wanted to perform PCA on the stocks currently included in the index. See the Moneychimp site. From 1934 to 2006, the S&P returned an 'average' 12.81%. But the CAGR was 11.26%.  I wrote an article Average Return vs Compound Annual Growth to address this issue.  Interesting that over time only a few funds have managed to get anywhere near this return, but the low cost indexer can get the long term CAGR minus .05% or so, if they wish. For video games the S&amp;P home entertainment software index will probably work. For airlines there's the S&amp;P airlines index but that may not work well for private jets.  You should browse different S&amp;P indicies based on GICS classifications or any other indicies you may find and then download their returns for the past few years and run a regression analysis on excel. Find the correlation between the indicies and the stock you're looking at then select the index with the highest correlation. The net return reported to you (as a percentage) by a mutual fund is the gross return minus the expense ratio.  So, if the gross return is X% and the expense ratio is Y%, your account will show a return of (X-Y)%.  Be aware that X could be negative too. So, with Y = 1, If X = 10 (as you might get from a stock fund if you believe historical averages will continue), then the net return is 9% and you have lost (Y/X) times 100% = 10% of the gross return. If X = 8 (as you might get from a bond fund if you believe historical averages will continue), then the net return is 7% and you have lost (Y/X) times 100% = 12.5% of the gross return. and so on and so forth.  The numbers used are merely examples of the returns that have been obtained historically, though it is worth emphasizing that 10% is an average return, averaged over many decades, from investments in stocks, and to believe that one will get a 10% return year after year is to mislead oneself very badly. I think the point of the illustrations is that expense ratios are important, and should matter a lot to you, but that their impact is proportionately somewhat less if the gross return  is high, but very significant if the gross return is low, as  in money-market funds.  In fact, some money market funds which  found that X < Y have even foregone charging the expense ratio  fee so as to maintain a fixed $1 per share price.  Personally,  I would need a lot of persuading to invest in even a stock fund with 1% expense ratio. How do I calculate the adjusted real rate of return of an investment (such as mutual fund) after inflation and fees? I have always thought that you do this: (1 + nominal return - fees)/(1 + inflation) - 1, but I have been told that this is the wrong way to do it.   Additionally, what is the difference between real interest rate and inflation-adjusted return? "As the comments above have been trying to get across, the prospective employer is offering to pay you for the bonus/unvested compensation that you would be losing by jumping ship right now to go work for them.  They are not offering to buy any securities that you already hold, regardless of whether they're profitable or unprofitable. Example 1. You participate in your current company's 401(k), and your company matches your contributions at 50%.  However, the matching funds are not yours immediately; they vest in 20%/year increments until you have been at the company for 5 years.  Let's say you've been there for 3 years and have contributed $50K to the plan.  Your company has matched you at $25K, but only 60% of that ($15K) has vested.  If you leave right now for the new employer, you're leaving $10K behind.  So the new employer might offer to ""buy out"" (i.e. pay you) that $10K to help encourage you to switch now.  You might then counter their offer by pointing out that if you stay where you are that $10K is coming to you tax-deferred, whereas their $10K signing bonus would be taxed.  So you ask for $15K instead. Example 2. You work for a Wall Street investment bank.  Each December you receive a performance bonus.  Since you began working there, your three yearly bonuses have been (in chronological order) $500K, $750K, and $1M.  It's June, so you've worked halfway towards your next bonus.  You have a lot of incentive to NOT leave your current employer.  A competing employer may offer to ""buy you out"" of your anticipated bonus by giving you a $1.25M signing bonus (since you'd almost certainly not be eligible for a performance bonus during your first year there).  You might negotiate with them and say ""I'm on track for $2M this year"", and then they would figure out if you're really worth that much to them. So you can see this all has to do with the prospective employer trying to compensate you for any income you're already counting on receiving from your current employer.  By jumping ship now you would be foregoing that guaranteed/expected income, so the competitor wants to remove that anchor that might be holding you back from making the move. Stocks/options that you already own are irrelevant to the prospective employer.  Since you wouldn't be giving those up by changing jobs, there's no reason for them to factor into the equation."