For every trade you will incur some transaction cost. You may think that even though there is a Bid and an Ask price, you may on average get somewhere in the mi

For every trade you will incur some transaction cost. You may think that even though there is a Bid and an Ask price, you may on average get somewhere in the middle, but you don't. Your buy trades are likely to be filled on the Ask price and your sell trades are likely to be filled on the Bid price because some intermediary will get in between and pocket the spread. This has been the case, this is the case, and I haven't seen viable solutions to this what so ever. What has changed over the past decade is who that intermediary is and how much of the spread they can steal. In 2001 New York Stock Exchange reduced the minimum listed price increments from $1/8 to $.01 . This spread used to be collected by exchange "specialists" with inherited seats on the floor for providing liquidity. The rise of alternative exchanges and computers allowed third parties to cut in to provide liquidity with smaller spreads and cutting out the specialists. These third parties are high frequency traders. Investors are still loosing the spread on each trade they make, but it is so much less than it used to be. There are issues with the market microstructures that could be addressed, but trying to push computer generated should not be it. I for one, never want to go back to the dark days of specialists and their $.125 and $.25 spreads. PS. This was a discussion of the minimum transaction cost you can have. Additionally you may have to pay fees to your broker ( especially if you are retail and don't trade a lot ). If you are trading lots of shares at a clip you will also encounter costs from the market impact of your trades.