In February Nasdaq launched an AIR application that tracks every bid and ask price on a stock.

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So the bid and ask price will be the same as it would be on an exchange.

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By creating a tax wedge between the bid and ask price of financial assets, the APT tax provides incentives to lengthen the average holding period of financial instruments.

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Dark pools are known for cutting costs as some venues allow trading at the midpoint between the bid and the ask price.

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The best way to protect yourself is to use limit orders when placing an order to buy or sell a stock or an exchange-traded fund. (See How Your Buy and Sell Orders Get Filled for more.) Look at the bid-ask spread and set your price limit at the bid for selling a stock and at the ask for buying a stock.

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In the example, the spread is 0.15% (that is the bid subtracted from the ask, divided by the share price and multiplied by 100).

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