The currency conversion is applied only once - at the position closure. If the position is still open, it is included in the live result. To use your example:
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Your account is in GBP
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You are opening a long position with the Apple CFD at 241.27 USD
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You exit the position at 245.35 USD
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The USD/GBP exchange rate at the closure of the position is: 0.8126
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The quantity is 10 units
In order to calculate the result of the position in USD you apply the following formula: quantity * (closing price - opening price) = 10 * (245.35 USD - 241.27 USD) = 10 * 4.08 USD = 40.8 USD
In order to convert the result, you have to subtract the 0.5% conversion fee from the exchange rate first: 0.8126 - 0.5% = 0.8085
Thus your result in GBP looks like this: 40.8 USD x 0.8085 = 32.99 GBP
P.S. If the position is still open, you have to substitute ‘closing price’ with ‘current price’ in the formula