Keeping your tax records » Keeping records of income in different currency » Go to message

I am a self-employed writer, how do I keep records of my income in different currency? For example, my client is from the US and pays in dollars, therefore the invoice is in dollars as well. However, this income obviously appears on my bank account in pounds.

Is invoice in dollars enough as a record? Or do I have to keep record of currency exchange rate on that particular day? Or some other kind of document proving that this is the same money?

Thanks in advance.