In trading, interest refers to the fees associated with holding leveraged positions overnight. When you hold a leveraged position beyond the trading day, an interest charge is applied. This interest is calculated based on the opening price, position volume, and the applicable interest rate. 

These interest charges can vary and may change without prior notice. The notation "Interest Buy/Sell: -7% / -7%" in your leverage account indicates the yearly interest rate applied to your positions. 

A negative percentage signifies that you will incur a cost for holding a leveraged position overnight. 

How to calculate interest? 

<Opening price> * <Position volume> * <Interest (%) / 100 / 360> 

Example: Twitter: 100 shares, long position, interest - 7% 25 * 100 * (-7%) / 100 / 360 = (-0,49) USD