Funding is the rent on a perp
Every 8 hours the perp charges or pays funding; over time it adds up to a meaningful cost or income. Factor it into any multi-day trade. Turn it into an edge on the funding arbitrage calculator.
The 8-hour rent on your position
Perpetual futures charge funding every 8 hours: position size × funding rate, paid by longs to shorts when the rate is positive (the usual state). It looks negligible — 0.01% — and compounds into the biggest hidden cost in leveraged holding.
The arithmetic that surprises: funding applies to the full position, not your margin. At 20x, a 0.01% rate costs 0.2% of your margin every 8 hours — 0.6% daily, 18% a month. Your trade can be right on direction and still bleed out on rent. This single line item explains most "the chart went up but I lost money" complaints.
Rate context: 0.01%/8h is baseline. Bull-market euphoria pushes rates to 0.05–0.1% — at 0.1% and 20x, funding alone consumes 6% of margin daily, and suddenly the crowded long trade has a countdown timer. Check the rate and compute the daily cost before entry; if the carry exceeds your expected daily edge, the position is upside-down before it starts.