There are two factors for daily cost/revenues associated with short selling of stocks and bonds at IBKR:
TWS shows the following data for AAPL. The Fee rate* column reflects the Borrow Fee the account will be charged and shown on the account statement.
*TWS Fee rates are indicative intraday and may change due to market conditions between trade execution and settlement.
Rates are based on a one-day look-back. The statement above is as of 6/21/2017 with a value date of 6/20/2017. That means the fee is being charged for holding the stock over market close on 6/20/2017.
This is the cash collateral mark used to calculate interest. To see more information on collateral marks and how they are calculated, please see this page: Short Sale > Collateral
Collateral cash value.
The annualized percentage borrow fee the account is charged.
The cash amount the account will be charged to borrow AAPL for 6/20/2017.
IBKR pays interest on Short Sale Proceeds based on the following schedule, calculated on the total short balance of the account.
The Short Sale Proceeds Interest rate that IBKR would pay an account with a short balance of USD 5,000,000 is 0.628% (assuming the benchmark is 1.16%), computed as a weighted average of the tiers.
The weighted average rate can be computed on the calculator here.
The net cost/revenue to short AAPL for an account with USD 5,000,000 in short balances is a credit of 0.378%, or USD 0.15 per day, as illustrated in this chart:
Taking into account the Weighted Average Short Sale Proceeds Interest on a balance of USD 5,000,000 (similar to the AAPL example above) of 0.628%, the net borrow cost/revenue is -49.56%, or a debit of USD 2.48 per day.
For the purposes of crediting interest on cash equal to short stock collateral values, only accounts with Net Asset Value (NAV) exceeding USD 100,000 will be eligible to receive credit interest on these cash balances.
|USD||0 - 100,000||0%|
|100,000.01 - 1,000,000||0% (BM - 1.25%)|
|1,000,000.01 - 3,000,000||0% (BM - 0.5%)|
|3,000,000.01 +||0% (BM - 0.25%)|
|AUD||0 - 140,000||0%|
|140,000.01 +||0% (BM - 2.25%)|
|CAD||0 - 130,000||0%|
|130,000.01 - 1,300,000||0% (BM - 1.75%)|
|1,300,000.01 - 3,000,000||0% (BM - 1.1%)|
|3,000,000.01 +||0% (BM - 0.9%)|
|CHF||0 - 90,000||-0.995% (BM - 0.25%)|
|90,000.01 +||-2.995% (BM - 2.25%)|
|EUR||0 - 90,000||-0.813% (BM - 0.25%)|
|90,000.01+||-2.813% (BM - 2.25%)|
|GBP||0 - 80,000||0%|
|80,000.01+||0% (BM - 2.25%)|
|HKD||0 - 780,000||0%|
|780,000.01||0% (BM - 2.25%)|
|MXN||0 - 2,000,000||0%|
|2,000,000.01+||1.91% (BM - 4%)|
|SEK||0 - 900,000||-0.411% (BM - 0.25%)|
|900,000.01+||-2.411% (BM - 2.25%)|