Is interest paid/charged on long/short Virtual FX currency positions?

To see your actual, real-time currency balances, from the Account window in TWS or the Balances section of the Portfolio in IBKR Desktop, check the Total Cash and Settled Cash fields of the Market Value - Real FX Balance…

The FX Portfolio - Virtual FX Positions section of the Account window is designed to show activity for currency pair trades for FX traders so that they can track average cost and running P&L on their currency trades.

• Since the "Position" value may reflect the sum of trades executed in the FX market along with currency conversions to change non-base funds into your base currency, these “virtual” positions do not necessarily reflect an actual cash balance in any currency…

No, it is not possible to designate more than one base currency on your account. Please note that despite the fact that you must choose a single base currency, you may hold cash balances in multiple currencies in your account.

Additional Information…

Interest is calculated by IBKR daily on a per currency basis, and is reflected on client statements in an accrued state. It is important to note that interest is calculated on settled funds, therefore, if you close a negative cash balance through a trade on Monday, interest will continue to accrue on the negative balance until the trade settles…