Fathom's default historical exchange rates are sourced from Open Exchange Rates. We use an inter-bank (without retail fluctuations), mid-market (average of buy/sell rates), rate which is calculated end-of-day using an average of rates from the preceding day.
For monthly data, Fathom uses the average exchange rate over the month to translate the Profit & Loss accounts and the month end exchange rate for translating Balance Sheet accounts.
Future periods will use the exchange rates from the most recently completed month.
For example, if the report is run in the middle of January, we will use the average exchange rate for December for the Profit & Loss and the end of month exchange rate for December for the Balance Sheet for January and all future periods.
Can I provide my own exchange rates?
Yes! You can specify your own custom historical exchange rates within Fathom for P&L and Balance sheet. View the following help article for more information: Customising Foreign Exchange Rates.