How does high frequency trading work if money isn't available for 2-3 days after selling?
Margin accounts do not have the problem you are imagining, which is unique to cash accounts High frequency trades are intra day. The would buy a stock for 100 and sell for 100.10 multiple times. So If you start with 100 in your broker account, you buy something [it takes 2-3 days to settle], you sell for 100.10 [it takes 2-3 days to settle]. You again buy something for 100. It is the net value of both buys and sells that you need to look at. Trading on Margin Accounts. Most brokers offer Margin Accounts. The exact leverage ratios varies. What this means is that if you start with 10 [or 15 or 25] in your broker you can buy stock of 100. Of course legally you wont own the stock unless you pay the broker balance, etc. Purchases and sales from the same trade date will both settle on the same settlement date. They don't have to pay for their purchases until later either. Because HFT typically make many offsetting trades -- buying, selling, buying, selling, buying, selling, etc -- when the purchases and sales settle, the amount they pay for their purchases will roughly cancel with the amount they receive for their sales (the difference being their profit or loss). Margin accounts and just having extra cash around can increase their ability to have trades that do not perfectly offset. In practice, the HFT's broker will take a smaller amount of cash (e.g. $1 million) as a deposit of capital, and will then allow the HFT to trade a larger amount of stock value long or short (e.g. $10 million, for 10:1 leverage). That $1 million needs to be enough to cover the net profit/loss when the trades settle, and the broker will monitor this to ensure that deposit will be enough. "As previously answered, the solution is margin. It works like this: You deposit e.g. 1'000 USD at your trading company. They give you a margin of e.g. 1:100, so you are allowed to trade with 100'000 USD.  Let's say you buy 5'000 pieces of a stock at $20 USD (fully using your 100'000 limit), and the price changes to $20.50 . Your profit is 5000* $0.50 = $2'500. Fast money? If you are lucky. Let's say before the price went up to 20.50, it had a slight dip down to $19.80. Your loss was 5000* $0.2 = 1'000$. Wait! You had just 1000 to begin with: You'll find an email saying ""margin call"" or ""termination notice"": Your shares have been sold at $19.80 and you are out of business. The broker willingly gives you this credit, since he can be sure he won't loose a cent. Of course you pay interest for the money you are trading with, but it's only for minutes. So to answer your question: You don't care when you have ""your money"" back, the trading company will always be there to give you more as long as you have deposit left. (I thought no one should get margin explained without the warning why it is a horrible idea to full use the ridiculous high margins some broker offer. 1:10 might or might not be fine, but 1:100 is harakiri.)"
My take on this is that this reduces your liquidity risk. Stocks, bonds and many other investment vehicles on secondary markets you may think of are highly liquid but they still require that markets are open and then an additional 3-5 business days to settle the transaction and for funds to make their way to your bank account.  If you require funds immediately because of an emergency, this 3-5 business days (which gets longer as week-ends and holidays are in the way) can cause a lot of discomfort which may be worth a small loss in potential ROI.  Think of your car breaking down or a water pipe exploding in your home and having to wait for the stock sale to process before you can make the payment. Admittedly, you have other options such as margin loans and credit cards that can help absorb the shock in such cases but they may not be sufficient or cause you to pay interest or fees if left unpaid. If you look at a trade grid you can see how this happens. If there are enough bids to cover all shares currently on the sell side at a certain price, those shares will be bought and increased price quotes will be shown for the bids and ask. If there are enough bids to cover this price, those will get bought and higher prices will be shown and this process will repeat until the sell side has more power than the buy side. It seems like this process is going on all day long with momentum either on the upside or downside. But I think that much of this bidding and selling is automatic and is being done by large trading firms and high tech computers. I also feel that many of these bids and asks are already programmed to appear once there is a price change. So once one price gets bought, computers will put in higher bids to take over asks. It's like a virtual war between trading firms and their computers. When more money is on the buy side the stock will go up, and vice versa. I sort of feel like this high-frequency trading is detrimental to the markets and doesn't really give everyone a fair shot. Retail investors do not have the resources and knowledge in order to do this sort of high frequency trading. It also seems to go against certain free market principles in my opinion. If #2 is how it really worked I would approve.  In the real world, entities who have the money to purchase access have systems which are in a position to execute strategies which shave pennies of of people who want to make real trades. I want to sell for $61.15 and someone wants to buy for $61.10 and the HFT traders force both hands and make their money on that nickel in between us. You pointed out that HFT does not create ipods are mine minerals.  Neither does human trading. HFT is a proxy for human trading.  Although the computer is executing trades automatically based on an algorithm, it is still using money from a human being's account so the trading is still being done with someone's money. Fast execution of trades is desirable in exchanges.  Imagine two exchanges:  One only executes trades once a month, the other executes trades once a week.  Which exchange would be more desirable?  The exchange that trades once a week.  Why?  Because if I'm holding a stock that I would like to sell, I want to sell it now - not a month from now.  Same reason for buying.  This concept works all the way down to seconds and fractions of seconds. The issue with HFT, however, is there are cases where the market goes against the HFT algorithm and the algorithm continues to execute trades driving prices up or down by large amounts in the matter of minutes or even seconds. The exchange frequently cancels these trades which only encourages more aggressive HFT trading since HFT traders can have their losses cancelled.  This is a privilege that LFTs (low frequency traders) do not receive.  This is a valid criticism of HFTs. A short list of such cancelled trades: 8/26/2010: Nasdaq cancels trades of CORE stock 10/4/2010: Nasdaq cancels trades of CENX stock 10/15/2010: NYSE cancels trades of PAY stock 10/18/2010: NYSE cancels $500 million worth of SPY trades 5/18/2011: NYSE cancels 15,900 trades of BEE.PR.C 6/21/2011: Nasdaq cancels CNTY trades 12/2/2011: London Metals Exchange cancel trades of copper How come when I sell stocks, the brokerage won't let me cash out for three days, telling me the SEC requires this clearance period for the transaction to clear, but they can swap shit around in under a second?   Be interesting to see what would happen if *every* transaction wasn't cleared until the closing bell. "That amount of shares is too low to create ""ripples"" in the market. Usually you don't specify the price to sell the stock, unless you are personally on the floor trading the securities. And even then, with a volume of $50,000 it would just mean you threw away $45,000. For most people it would mean setting a $5 sell order, and the broker would understand that as ""sell this security so long the price is above $5"". When you get to the trading volume required to influence the price, usually you are also bound by some regulations banning some moves. One of them is the Pump and Dump, and even if you are suggesting the opposite, it might be in preparation of this scam. Also, the software used for High Frequency Trading (what all the cool kids[a] in Wall Street are using these days) employ advanced (and proprietary) heuristics to analyze the market and make thousands of trades in a short interval of time. On HTF's speed: Decisions happen in milliseconds, and this could result in big market moves without reason.  So a human trader attempting to manipulate the market versus these HTF setups, would be like a kid in a tricile attempting to outrun the Flash (DC comics). [a] Cool Kid: not really kids, more like suited up sharks. Money-eating sharks." Yes there will be enough liquidity to sell your position barring some sort of Flash Crash anomaly. Volume generally rises on the day of expiration to increase this liquidity. Don't forget that there are many investment strategies--buying to cover a short position is closing out a trade similar to your case. At any given time there are buy orders and there are sell orders.  Typically there is a little bit of space between the lowest sell order and the highest buy order, this is known as the bid/ask spread.  As an example say person A will sell for $10.10 but person B will only buy at $10.00.  If you have a billion shares outstanding just the space between the bid and ask prices represents $100,000,000 of market cap. Now imagine that the CEO is in the news related to some embezzlement investigation.  A number of buyers cancel their orders.  Now the highest buy order is $7.  There isn't money involved, that's just the highest offer to buy at the time; but that's a drop from $10 to $7.  That's a change in market cap of $3,000,000,000.  Some seller thinks the stock will continue to fall, and some buyer thinks the stock has reached a fair enterprise value at $7 billion ($7 per share).  Whether or not the seller lost money depends on where the seller bought the stock.  Maybe they bought when it was an IPO for $1.  Even at $7 they made $6 per share. Value is changing, not money.  Though it would be fun, there's no money bonfire at the NYSE. Many of the Bitcoin exchanges mimic stock exchanges, though they're much more rudimentary offering only simple buy/sell/cancel orders.  It's fairly normal for retail stock brokerage accounts to allow other sorts of more complex orders, where once a certain criteria is met, (the price falls below some $ threshold, or has a movement greater than some %) then your order is executed.  The space between the current buy order and the current sell order is the bid/ask spread, it's not really about timing.  Person X will buy at $100, person Y will sell at $102.  If both had a price set at $101, they would just transact.  Both parties think they can do a little bit better than the current offer.  The width of the bid/ask spread is not universal by any means.  The current highest buy order and the current lowest sell order, are both the current price.  The current quoted market price is generally the price of the last transaction, whether it's buy or sell. A tax is the wrong way to go. HFT does not create liquidity, it only creates arbitrage opportunities and is quite possibly illegal given current laws and regulation.  There needs to be a required minimum order time on market. HFT just naturally goes away if their orders have to hang out for 5 seconds. There's a lot of hype about HFT. It involves computers doing things that people don't really understand and making a bunch of rich guys a bunch of money, and there was a crisis and so we hate rich wall street guys this year, and so it's a hot-button issue. Meh. There's some reason for concern about the safety of the markets, but I think there's also a lot more of people trying to sell you a newspaper. Remember that while HFT may mean there are a lot of trades, the buying and the selling add up to the same thing. Meanwhile, people who buy stock to hold on to it for significant periods of time will still affect the quantity of stock out there on the market, applying pressure to the price, buying and selling at the prices that they think the security is worth.  As a result, it's unlikely that high-frequency trading moves the stock price very far from the price that the rest of the market would determine for very long; if it did, the lower-frequency traders could take advantage of it, buying if it's too low and selling if it's too high. How long do you plan to hold a stock? If you're trying to do day-trading, you might have some trouble; these people are competing with you to do the same thing, and have significant resources at their disposal. If you're holding onto your stock for years on end (like you probably should be doing with most stock) then a trivial premium or discount on the price probably isn't going to be a big deal for you. This is often the case where traders are closing out short positions they don't want to hold overnight, for a variety of reasons that matter to them.  Most frequently, this is from day traders or high-frequency traders settling their accounts before the markets close. "I'm just trying to visualize the costs of trading. Say I set up an account to trade something (forex, stock, even bitcoin) and I was going to let a random generator determine when I should buy or sell it. If I do this, I would assume I have an equal probability to make a profit or a loss. Your question is what a mathematician would call an ""ill-posed problem.""  It makes it a challenge to answer.  The short answer is ""no.""  We will have to consider three broad cases for types of assets and two time intervals. Let us start with a very short time interval.  The bid-ask spread covers the anticipated cost to the market maker of holding an asset bought in the market equal to the opportunity costs over the half-life of the holding period.  A consequence of this is that you are nearly guaranteed to lose money if your time interval between trades is less than the half-life of the actual portfolio of the market maker.  To use a dice analogy, imagine having to pay a fee per roll before you can gamble.  You can win, but it will be biased toward losing. Now let us go to the extreme opposite time period, which is that you will buy now and sell one minute before you die.  For stocks, you would have received the dividends plus any stocks you sold from mergers.  Conversely, you would have had to pay the dividends on your short sales and received a gain on every short stock that went bankrupt.  Because you have to pay interest on short sales and dividends passed, you will lose money on a net basis to the market maker.  Maybe you are seeing a pattern here.  The phrase ""market maker"" will come up a lot. Now let us look at currencies.  In the long run, if the current fiat money policy regime holds, you will lose a lot of money.  Deflation is not a big deal under a commodity money regime, but it is a problem under fiat money, so central banks avoid it.  So your long currency holdings will depreciate.  Your short would appreciate, except you have to pay interest on them at a rate greater than the rate of inflation to the market maker. Finally, for commodities, no one will allow perpetual holding of short positions in commodities because people want them delivered.  Because insider knowledge is presumed under the commodities trading laws, a random investor would be at a giant disadvantage similar to what a chess player who played randomly would face against a grand master chess player.  There is a very strong information asymmetry in commodity contracts.  There are people who actually do know how much cotton there is in the world, how much is planted in the ground, and what the demand will be and that knowledge is not shared with the world at large.  You would be fleeced. Can I also assume that probabilistically speaking, a trader cannot do   worst than random? Say, if I had to guess the roll of a dice, my   chance of being correct can't be less than 16.667%. A physicist, a con man, a magician and a statistician would tell you that dice rolls and coin tosses are not random.  While we teach ""fair"" coins and ""fair"" dice in introductory college classes to simplify many complex ideas, they also do not exist.  If you want to see a funny version of the dice roll game, watch the 1962 Japanese movie Zatoichi.  It is an action movie, but it begins with a dice game.   Consider adopting a Bayesian perspective on probability as it would be a healthier perspective based on how you are thinking about this problem.  A ""frequency"" approach always assumes the null model is true, which is what you are doing.  Had you tried this will real money, your model would have been falsified, but you still wouldn't know the true model. Yes, you can do much worse than 1/6th of the time.  Even if you are trying to be ""fair,"" you have not accounted for the variance. Extending that logic, then for an inexperienced trader, is it right to   say then that it's equally difficult to purposely make a loss then it   is to purposely make a profit? Because if I can purposely make a loss,   I would purposely just do the opposite of what I'm doing to make a   profit. So in the dice example, if I can somehow lower my chances of   winning below 16.6667%, it means I would simply need to bet on the   other 5 numbers to give myself a better than 83% chance of winning. If the game were ""fair,"" but for things like forex the rules of the game are purposefully changed by the market maker to maximize long-run profitability.  Under US law, forex is not regulated by anything other than common law.  As a result, the market maker can state any price, including prices far from the market, with the intent to make a system used by actors losing systems, such as to trigger margin calls.  The prices quoted by forex dealers in the US move loosely with the global rates, but vary enough that only the dealer should make money systematically.  A fixed strategy would promote loss. You are assuming that only you know the odds and they would let you profit from your 83.33 percentage chance of winning. So then, is the costs of trading from a purely probabilistic point of   view simply the transaction costs? No matter what, my chances cannot   be worse than random and if my trading system has an edge that is   greater than the percentage of the transaction that is transaction   cost, then I am probabilistically likely to make a profit? No, the cost of trading is the opportunity cost of the money.  The transaction costs are explicit costs, but you have ignored the implicit costs of foregone interest and foregone happiness using the money for other things. You will want to be careful here in understanding probability because the distribution of returns for all of these assets lack a first moment and so there cannot be a ""mean return.""  A modal return would be an intellectually more consistent perspective, implying you should use an ""all-or-nothing"" cost function to evaluate your methodology." Day traders see a dip, buy stocks, then sell them 4 mins later when the value climbed to a small peak. What value is created? Is the company better off from that trade? The stocks were already outside of company hands, so the trade doesn't affect them at all. You've just received money from others for no contribution to society. A common scenario is a younger business having a great idea but not enough capital funds to actually get the business going. So, investors buy shares which they can sell later on at a higher value. The investor gets value from the shares increasing over time, but the business also gets value of receiving money to build the business. You'd need millions of dollars to trade the number of shares it would take to profit from these penny variations.  What you bring up here is the way high frequency firms front-run trades and profit on these pennies. Say you have a trade commission of $5.  Every time you buy you pay $5, every time you sell you pay $5.  So you need a gain in excess of $10, a 10% gain on $100.  Now if you wanted to trade on a penny movement from $100 to $100.01, you need to have bought 1,000 shares totaling $100,000 for the $0.01 price movement to cover your commission costs.  If you had $1,000,000 to put at risk, that $0.01 price movement would net you $90 after commission, $10,000,000 would have made you $990.  You need much larger gains at the retail level because commissions will equate to a significant percentage of the money you're investing. Very large trading entities have much different arrangements and costs with the exchanges.  They might not pay a fee on each transaction but something that more closely resembles a subscription fee, and costs something that more closely resembles a house. Now to your point, catching these price movements and profiting.  The way high frequency trading firms purportedly make money relates to having a very low latency network connection to a particular exchange.  Their very low latency/very fast network connection lets them see orders and transact orders before other parties.   Say some stock has an ask at $101 x 1,000 shares.  The next depth is $101.10.  You see a market buy order come in for 1,000 shares and place a buy order for 1,000 shares at $101 which hits the exchange first, then immediately place a sell order at $101.09, changing the ask from $101.00 to $101.09 and selling in to the market order for a gain of $0.09 per share.