Utilize your financial knowledge, give your answer or opinion to the input question or subject . Answer format is not limited.

How does high frequency trading work if money isn't available for 2-3 days after selling?
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.)