The collateral amount underlying the security loan via the Stock Yield Enhancement Program and used for determining interest payments is calculated using standard industry convention. In the US market, the closing price of the stock is multiplied by 102% and then rounded up to the nearest whole dollar. The collateral is marked-to-market daily and the activity will be displayed on your statement.
Example
The collateral mark price of a stock which closed at $98 would be $100.
Calculation: 98 closing price * 1.02 = 99.96. Rounded up to the nearest whole dollar = 100
For an SYEP loan of 100 shares, IBKR will provide you with $10,000 of collateral value (100 collateral mark * 100 shares on loan).
The interest rate will be paid based on $10,000 of collateral value, not $9,800.
The full list of collateral mark price calculations for other currencies is available here.
Warning: These figures are estimates only. They are not a reliable guide to the future performance of this program.