How to compute real return including expense ratio
Returns reported by mutual funds to shareholders, google, etc. are computed after all the funds' costs, including Therefore the returns you see on google finance are the returns you would actually have gotten.
The main question is, how much money you want to make?  With every transaction, you  should calculate the real price as the price plus costs. For example, if you but 10 GreatCorp stock of £100 each, and the transaction cost is £20 , then the real cost of buying a single share is in fact buying price of stock + broker costs / amount bought, or £104 in this case.  Now you want to make a profit so calculate your desired profit margin. You want to receive a sales price of buying price + profit margin + broker costs / amount bought. Suppose that you'd like 5%, then you'll need the price per stock of my example to increase to 100 + 5% + £40 / 10 = £109.  So you it only becomes worth while if you feel confident that GreatCorp's stock  will rise to that level. Read the yearly balance of that company to see if they don't have any debt, and are profitable. Look at their dividend earning history. Study the stock's candle graphs of the last ten years or so, to find out if there's no seasonal effects, and if the stock performs well overall. Get to know the company well. You should only buy GreatCorp shares after doing your homework.  But what about switching to another stock of LovelyInc? Actually it doesn't matter, since it's best to separate transactions. Sell your GreatCorp's stock when it has reached the desired profit margin or if it seems it is underperforming. Cut your losses! Make the calculations for LovelyCorp's shares without reference to GreatCorp's, and decide like that if it's worth while to buy. The expense ratio is 0.17% so doesnt that mean that for every 10K I   keep in the money market fund I lose $17/year?  Not really. The expense ratio is taken before distributions are paid which applies to all mutual funds. Should I care about this?  In this case not really. If it was a taxable account, then other options may be more tax-efficient that is worth noting. The key with money market funds is that the expense ratio often represents how much money the administrators will take before paying out the rest. So, if your money market fund bought investments that paid .25% then you'd likely see .08% as that is what is left over after the .17% is taken in the dividends. If at the start of the year, the funds NAV is $1, and at the end of   the year, the funds NAV is still $1, I havent lost anything right? Right. Wikipedia has a good article on money market funds. Keep in mind that most money market funds are run as one of a number of funds from a fund family that may have to take a little less profit on the money market funds when rates are low. Research Affiliates expects a 10-year real return of about 1.3% on REITs.  See the graph on Barry Ritholtz's blog.  Here's a screenshot from the Research Affiliates website that shows how they calculated this expected return: It is a good enough approximation. With a single event you can do it your way and get a better result, but imagine that the $300 are spread over a certain period with $10 contribution each time? Then recalculating and compounding will be a lot of work to do. The original ROI formula is averaging the ROI by definition, so why bother with precise calculations of averages that are imprecise by definition, when you can just adjust the average without losing the level of precision? 11.4 and 11.3 aren't significantly different, its immaterial. You could take these definitions from MSCI as an example of how to proceed.  They calculate price indices (PR) and total return indices (including dividends).  For performance benchmarks the net total return (NR) indices are usually the most relevant. In your example the gross total return (TR) is 25%. From the MSCI Index Defintions page :- The MSCI Price Indexes measure the price performance of markets   without including dividends. On any given day, the price return of an   index captures the sum of its constituents’ free float-weighted market   capitalization returns. The MSCI Total Return Indexes measure the price performance of markets   with the income from constituent dividend payments. The MSCI Daily   Total Return (DTR) Methodology reinvests an index constituent’s   dividends at the close of trading on the day the security is quoted   ex-dividend (the ex-date). Two variants of MSCI Total Return Indices are calculated: With Gross Dividends: Gross total return indexes reinvest as much as possible of a company’s   dividend distributions. The reinvested amount is equal to the total   dividend amount distributed to persons residing in the country of the   dividend-paying company. Gross total return indexes do not, however,   include any tax credits. With Net Dividends: Net total return indexes reinvest dividends after the deduction of   withholding taxes, using (for international indexes) a tax rate   applicable to non-resident institutional investors who do not benefit   from double taxation treaties. I was emailing back and forth with a manager in a different department on how real returns are being calculated, and he said that the industry standard is 1 + real returns*(1+inflation) - fees, and to not use my formula because it can double count inflation, making fees lower. However, real returns are not observable in the future, and I do not why he uses that formula. The returns were used in an Excel spreadsheet.   What are your thoughts about this? 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. Should you care? From Vanguard: The long-term impact of investment costs on portfolio balances   Assuming a starting balance of $100,000 and a yearly return of 6%, which is reinvested Check out this chart, reflecting the impact of relatively small expense ratios on your 30 year return:  All else being equal you should very much care about expense ratios. You end up with a significantly smaller amount if your pre-expense return is the same. A 0.75% difference in ER compounds to 20% over 30 years. If so, how should I take them into consideration when comparing funds? I'm in the U.S. if that matters. If they track the same index, cheaper is better. The cases where higher expense ratios might be better are if you believe that index will outperform the market by enough to recoup the cost of the ER.  There is significant research that most funds do not do this. For this, the internal rate of return is preferred. In short, all cash flows need to be discounted to the present and set equal to 0 so that an implied rate of return can be calculated. You could try to work this out by hand, but it's practically hopeless because of solving for roots of the implied rate of return which are most likely complex. It's better to use a spreadsheet with this capability such as OpenOffice's Calc. The average return on equity is 9%, so anything higher than that is a rational choice. Example Using this simple tool, the formula variables can easily be input. For instance, the first year has a presumed cash inflow of $2,460 because the insurance has a 30% discount from $8,200 that is assumed to be otherwise paid, a cash inflow of $40,000 to finance the sprinklers, a cash outflow of $40,000 to fund the sprinklers, a $400 outflow for inspection, and an outflow in the amount of the first year's interest on the loan. This should be repeated for each year.  They can be input undiscounted, as they are, for each year, and the calculator will do the rest. PE ratio is the current share price divided by the prior 4 quarters earnings per share. Any stock quote site will report it. You can also compute it yourself. All you need is an income statement and a current stock quote. A couple ideas: Use excel - it has an IRR (internal rate of return) that can handle a table of inputs as you describe, along with dates deposited to give you a precise number.  Go simple - track total deposits over the year, assume half of that was present in January. So, for example, your account started the year with $10k, ended with $15k, but you deposited $4k over the year. It should be clear the return (gain) is $1k, right? But it's not 10%, as you added during the year. I'd divide $1k/$12k for an 8.3% return. Not knowing how your deposits were structured, the true number lies between the 10% and 6.7% as extremes. You'll find as you get older and have a higher balance, this fast method gaining accuracy, as your deposits are a tinier fraction of your account and likely spread out pretty smoothly over the year anyway. This link does it ok:  http://investexcel.net/1979/calculate-historical-volatility-excel/ Basically, you calculate percentage return by doing stock price now / stock price before.  You're not calculating the rate of return hence no subtraction of 100%.  The standard is to do this on a daily basis: stock price today / stock price yesterday. The most important and most misunderstood part is that you now have to analyze the data geometrically not arithmetically.  To easily do this, convert all percentage returns with the natural log, ln(). Next, you take the standard deviation of all of those results, and apply exp().  This answers the title of your question. For convenience's sake, it's best to annualize since volatility (implied or statistical) is now almost always quoted annualized.  There are ~240 trading days each year.  You multiply your stdev() result by (240 / # of trading days per return) ^ 0.5, so if you're doing this for daily returns, multiply the stdev() result by 240^0.5; if you were doing it weekly, you'd want to multiply by (240 / ~5)^0.5; etc.  This is your number for sigma.  This answers the intent of your question. For black-scholes, you do not convert anything back with exp(); BS is already set up for geometric analysis, so you need to stay there. The reason why analysis is done geometrically is because the distribution of stock returns is assumed to be lognormal (even though it's really more like logLaplace). "I could not figure out a good way to make XIRR work since it does not support arrays.  However, I think the following should work for you: Insert a column at D and call it ""ratio"" (to be used to calculate your answer in column E).  Use the following equation for D3: =1+(C3-B3-C2)/C2 Drag that down to fill in the column. Set E3 to: =(PRODUCT(D$3:D3)-1)*365/(A3-A$2) Drag that down to fill in the column. Column E is now your annual rate of return." TWRR = (2012Q4 x 2013Q1 x 2013Q2) ^ (1/3) = ?? (1.1 * .809 * 1.29) ^ (1/3) = 1.047 or 4.7% return. No imaginary numbers needed.  But. Your second line there is wrong $15,750 - $15,000 - $4,000 ? The $15K already contains the $4k, why did you subtract it again?  This a homework problem? In order to calculate the ratio you are looking for, just divide total debt by the market capitalization of the stock. Both values can be found on the link you provided. The market capitalization is the market value of equity.