Sole trader UK paid in US Dollars

When paid in US Dollars do I need to convert each payment into Sterling when received or do I do it monthly /annually using the HMRC currency monthly/annual average exchange rates? If I'm allowed to do it annually could I use the annual average published in March to complete 24/25 tax year figures even though that would cover 1st April to 31st March rather than the actual tax year. For example for tax year 24/25 could I use the March 25 figures even though that wouldn't technically cover 1/4/25 to 5/4/25?

Hi,

Under the terms of Self Assessment, we do not provide an official exchange rate and the onus is on the individual to use a just and reasonable exchange rate for each acquisition and disposal.  
For your convenience, there are exchange rates at:

The National Archives: Exchange rates from HMRC in CSV and XML format

For older rates at:

The National Archives: Foreign exchange rates and spot rates: 1 January 1989 to 31 March 2009

You are free to use any of the supplied rates or one of your own choosing.

Thank you.