If you've ever asked «what is perpetual» in derivatives terms, the answer is simple: it's a futures-style contract designed to track an underlying price indefinitely. Economist Robert Shiller proposed perpetual futures in 1992, but crypto made the product mainstream.
BitMEX's XBTUSD perpetual swap, announced on May 13, 2016, became the template the industry copied at scale. Traditional futures converge to spot because they have a calendar—CME Bitcoin futures, for example, expire on the last Friday of the month with a defined listing cycle.
That expiry forces convergence and requires traders to roll. Perpetual futures remove the roll. The market still needs a tether to spot, and that tether is funding.
Funding is the heartbeat of the perpetual contract. When a perp trades above spot—a premium—longs are typically the crowded side and pay shorts. When it trades below spot—a discount—shorts may pay longs.
Many major venues run funding on an every-8-hours cadence. Bybit, for instance, specifies a funding interval of three times per day and uses mark price as the liquidation trigger. Deribit explains the core principle bluntly: funding is not a fee the exchange pockets—on many designs, it is transferred directly between counterparties.
That design has two implications traders routinely underestimate. First, funding is a real cash flow that compounds into PnL even if the price goes nowhere. Second, funding is the market's positioning thermometer.
In a crowded long market, positive funding means the long side is paying rent to stay long. In a crowded short market, negative funding means shorts are paying to lean bearish.