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I bought a US stock (in US dollars) on 10 March 2021 and sold out (in US dollars) on 20 Dec 2023. I need to exchange the purchase price and disposal price to pounds to calculate the capital gain. I want to ask can I use the following currency exchange rates (from HRMC websites) to calculate: a) To use Average exchange rate (2020 Dec) to calculate purchase price on 10 March 2021 b) To use Spot exchange rate (2023 Dec) to calculate disposal price on 20 Dec 2023