Whereas quarterly futures expire, perpetual futures have funding payments every hour. Specifically, every hour, we measure the 1 hour TWAP of the perpetual future and the 1 hour TWAP of the underlying index:
If the perpetual is trading at a premium to the underlying index, long positions pay funding to the short positions. If the perpetual is trading at a discount to the underlying index, short positions pay funding to long positions. The funding rate to be paid/received is determined by the following formula:
position size * TWAP of ((future mark price - index) / index) / 24
This is similar to the future expiring once per day. In particular, if you sell a BTC perpetual future which is trading 0.10% above the underlying index all day, then over the course of the next day you will receive a total funding payment of 0.10%.
You can find historical funding rates here.
See Non-USD Collateral for more details.
In the event that your USD balance falls too far below zero (see below for details), some of your balances in the above coins may be automatically traded into USD by sending market orders into the corresponding FTX spot markets. You can choose whether to use FTT as collateral on the settings page. By default your account will use FTT as collateral. Note that Weight (total) is used to determine collateral for the purpose of liquidations, and Weight (free) is for the purpose of opening new positions.
Any positive PnL will be paid out in USD regardless of which type of collateral you use.