IBKR uses the midpoint of the bid/ask for the respective currency pair as reported by Reuters just prior to 4:00 PM ET.
You can see the exchange rates used in the Base Currency Exchange Rate section of your daily Activity Statements. Activity Statements are posted to the Client Portal under the Performance & Reports followed by Statements under Reports. Select Daily as the Period before you launch the statement.
Additional Information
- Information on the various sections of your Activity Statement in our Reporting Guide.