IB has added a risk premium for large margin balances. over $1,000,000 0.62% (BM + 0.5%) over $3,000,000 0.37% (BM + 0.25%) over $50,000,000 1.37% (BM + 1.25%) "IB charges a higher default interest rate for large debit cash balances. If you anticipate consistently having a large debit cash balance which would be affected by the Tier V interest rate, please contact the IB Funds & Banking department by telephone in order to arrange a review of the account balances and interest rates charged."