Does IB charge interest to short selling options on index futures? I tried to short selling 1 contract naked put on ESTX50 (euronext stoxx euro 50) in paper trade account and IB charged me interest like thousands of EUR. I thought that was because there's no EUR cash in my account balance, so I bought 18000 EUR and see what would happen. Next day, the interest was generated is all the same just like it was. Is there anyone know how to avoid the interest charged? Thanks.

Are you sure you're not confused with margin? Selling options naked will obviously require part of your account to be allocated as margin.
Before you execute the order on IB there's a 'check margin' option you can check.

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