Funding Rate Calculator

Perpetual futures never expire, so exchanges use a funding rate to keep the perp price tethered to spot. At each funding interval (usually every 8 hours) one side pays the other. When the rate is positive, longs pay shorts; when it is negative, shorts pay longs. You are charged on your notional (your full position size), not on your margin, so leverage multiplies the bill.

payment per interval = notional × funding_rate
total = payment per interval × number of intervals held
intervals held = floor(holding_hours / interval_hours)

The reason funding is dangerous is that it is invisible until it adds up. A 0.01% rate sounds like nothing, but it settles three times a day, which is about 10.95% a year. In a strong bull market the rate routinely climbs to 0.05-0.10% per 8 hours, which is roughly 55-110% annualized. A long that is right about direction can still bleed out just paying to stay open. This is the cost most traders never model before they hold a position for days.

How to use this. Put in your real position size, the current rate from your exchange, and how long you actually plan to hold. If the funding cost is a meaningful slice of your expected profit, the trade needs a bigger edge, a shorter hold, or the other side. A high positive rate is also a crowding signal: when everyone is long and paying to be long, the move is often late.

Leverage makes this sharper because it scales your notional. See exactly how with the leverage calculator, then practice on Hex37, where positions accrue real funding on live rates with fake money, so you feel the drain before it costs you anything.