The equation: notional × rate, on every fill
Fee = filled notional × fee rate, charged separately on the opening order and the closing order. Binance publishes the same formula for USDⓈ-M futures, and OKX's UAE help center charges opening and closing separately.
So a $10,000 balance that places one $1,000 round trip pays the same $1.10 as a $1,000 balance placing the same orders. Ten such round trips cost $11.00 on either account. Turnover, not balance, sets the bill.