1) Margin interest is only charged for leveraged positions held overnight.
2) For a long position, the daily interest= Borrowed Cash * Margin Rate/360.
|Margin Loan (USD)||Annual Margin Rate|
Let us assume you leveraged $30,000, held the position for two days, and then sold it. The margin interest charged will be [25,000 * 6.99% + (30000 - 25,000) * 6.49%] * 2/360 = $11.51. You will be charged $11.51 at the beginning of the next month.
Fees for short sale
For a short position, you need to borrow shares. The cost associated with a short sale is the fee for borrowing said stock. This fee changes every day for every available stock and is charged on a daily basis.