Stock market transaction cost calculation
"An order is your command to the broker to, say, ""sell 100 shares of AAPL"". An executed order (or partially executed order) is when all (or some) of that command is successfully completed. A transaction is an actual exchange of shares for money, and there may be one or more transactions per executed order.  For example, the broker might perform all of the following 5 transactions in order to do what you asked: On the other hand, if the broker cannot execute your order, then 0 transactions have taken place. The fee schedule you quote is saying that no matter how many transactions the broker has to perform in order to fill your order -- and no matter what the share prices are -- they're only going to charge you $0.005 per share ($0.50 in this example of 100 shares), subject to certain limits. However, as it says at the top of the page you linked, Our Fixed pricing for stocks, ETFs (Exchange Traded Products, or ETPs) and warrants charges a fixed amount per share or a set percent of trade value, and includes all IB commissions, exchange and most regulatory fees with the exception of the transaction fees, which are passed through on all stock sales. certain transaction fees are passed through to the client.  The transaction fee you included above is the SEC fee on sales.  Many (but not all) transaction fees DO depend on the prices of the shares involved; as a result they cannot be called ""fixed"" fees. For example, if you sell 100 shares of AAPL at $150 each, But if you sell 100 shares of AMZN at $940 each, So the broker will charge you the same $0.50 on either of those orders, but the SEC will charge you more for the expensive AMZN shares than for the cheaper AAPL shares. The reason this specific SEC fee mentions aggregate sales rather than trade value is because this particular SEC fee applies only to the seller and not to the buyer.  So they could have written aggregate trade value, but they probably wanted to highlight to the reader that the fee is only charged on sells."
They are providing you a service and they charge you for it. The service includes giving you a trading platform(website and the infrastructure), doing all the background work for setting up services for you, relaying your orders to the market or as a broker fulfilling your orders, doing settlement when an order is matched, giving you access to the stock market(the costs are quite high to get a license to relay orders to the market and I believe it needs to be renewed every year). There are transaction fees which the stock exchanges charge the brokers to use the stock markets infrastructure and connect to it. And then interfacing with banks for monetary transactions and also doing according to the law in the jurisdiction they are located in. Most of it is an one time cost, but they are a private enterprise out to make profit so they will charge for their services. The main difference between a mutual fund and an ETF are how they are bought and sold (from the investors perspective). An ETF is transacted on the open market. This means you normally can't buy partial shares with your initial investment. Having to transact on the open market also means you pay a market price. The market price is always a little bit different from the Net Asset Value (NAV) of the fund. During market hours, the ETF will trade at a premium/discount to the NAV calculated on the previous day. Morningstar's fund analysis will show a graph of the premium/discount to NAV for an ETF. With a mutual fund on the other hand, your investment goes to a fund company, which then grants you shares while under the hood buying the underlying investments. You pay the NAV price and are allowed to buy partial shares. Usually an ETF has a lower expense ratio, but if that's equal and any initial fees/commissions are equal, I would prefer the mutual fund in order to buy partial shares (so your initial investment will be fully invested) and so you don't have to worry about paying premium to NAV Calculating and adjusting cost basis accurately is a daunting task, but there is a (paid) online tool, NetBasis, which will automatically calculate and adjust your cost basis.  It is used by brokerage firms and Fortune 500 companies and is available to the public.  Go to netbasis.com. All you need are the purchase and sale dates and shares of the stock or mutual fund and the system has the rest of the information, such as corporate actions (splits, spin-offs, etc), pricing, and dividends and it also will apply the appropriate IRS rules for inherited and gifted shares. The regulation also gives investors the option to choose calculation methods.  Not only does NetBasis automatically calculate the method you choose, it will also give the results for all options and allow you to choose the best result. NetBasis also provides you with detailed supporting documentation which shows all of the calculations and the adjustments in chronological order. NetBasis has data going back as far as 1925, so it will accurately calculate cost basis for your old American Telegraph and Telephone shares. NetBasis also handles complex investment scenarios such as wash sales, short sales, return of capital, etc. Moderator's note: Disclosure: The answerer's profile indicates they are affiliated with NetBasis. He has included this on Schedule D line 1a, but I don't see any   details on the actual transaction. It is reported on form 8949. However, if it is fully reported in 1099-B (with cost basis), then you don't have to actually detail every position. Turbotax asked me to fill in individual stock sales with proceeds and cost basis information. ... Again, it seems to be documented on Schedule D in boxes 1a and 8a. See above. I received a 1099-Q for a 529 distribution for a family member. It was   used for qualified expenses, so should not be taxable. Then there's nothing to report. I believe I paid the correct amounts based on my (possibly flawed) understanding of estimated taxes. His initial draft had me paying a penalty. I explained my situation for the year, and his next draft had the   penalties removed, with no documentation or explanation. IRS assesses the penalty. If you volunteer to pay the penalty, you can calculate it yourself and pay with the taxes due. Otherwise - leave it to the IRS to calculate and assess the penalty they deem right and send you a bill. You can then argue with the IRS about that assessment. Many times they don't even bother, if the amounts are small, so I'd suggest going with what the CPA did. Simple math. Take the sale proceeds (after trade expenses) and divide by cost. Subtract 1, and this is your return. For example, buy at 80, sell at 100, 100/80 = 1.25, your return is 25%. To annualize this return, multiply by 365 over the days you were in that stock. If the above stock were held for 3 months, you would have an annualized return of 100%.  There's an alternative way to annualize, in the same example above take the days invested and dive into 365, here you get 4. I suggested that 25% x 4 = 100%. Others will ask why I don't say 1.25^4 = 2.44 so the return is 144%/yr. (in other words, compound the return, 1.25x1.25x...) A single day trade, noon to noon the next day returning just 1%, would multiply to 365% over a year, ignoring the fact there are about 250 trading days. But 1.01^365 is 37.78 or a 3678% return. For long periods, the compounding makes sense of course, the 8%/yr I hope to see should double my money in 9 years, not 12, but taking the short term trades and compounding creates odd results of little value. 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). Let's consider that transaction cost is 0(zero) for calculation. In the scenario you have stated, maximum profit that could be made is 55$, however risk is unlimited. Hedging can also be used to limit your losses, let's consider this scenario. Stock ABC trading @ 100$, I'll buy the stock ABC @ 100$ and buy a put option of ABC @ strike price 90$ for a premium of 5$ with an expiration date of 1 month. Possible outcomes I end up in a loss in 3 out of 4 scenarios, however my loss is limited to 15$, whereas profit is unlimited. While that sounds reasonable, it looks like most of the actual trading is done on the basis of changes rather than value.  At a guess, this is because computing the balance sheet anew with every change inhibits the speed with which transactions can be processed.