The funding rate is not a fee charged by the exchange — it is a peer-to-peer payment between longs and shorts, settled periodically (usually every 8 hours). Its purpose is to tether the perpetual's mark price to the underlying spot index.

Three components drive the rate:

Premium: (Mark Price − Index Price) / Index Price
Interest Rate: a fixed baseline (often 0.01% per 8h on many venues)
Clamp: a cap/floor limiting extreme rates

When perp trades above spot, funding is positive → longs pay shorts. When below, funding is negative → shorts pay longs.

Scenario	Mark vs Index	Funding	Who Pays
Bullish crowding	Mark > Index	Positive	Longs → Shorts
Bearish crowding	Mark < Index	Negative	Shorts → Longs
Balanced	Mark ≈ Index	≈ Interest Rate	Minimal flow