Fees & slippage eat the edge
Four taker fills round trip against a per-8h spread. Do the division before the trade, not after.
The cost stack
A two-leg trade fills four times: open long, open short, close long, close short. At a typical perp taker fee of 0.05-0.06% per fill, the fee bill alone is 0.20-0.24% of notional round trip. Add slippage — the gap between mid and your VWAP at size on each of the four fills — and adverse entry basis, and the all-in cost of touching the trade commonly lands between 0.3% and 0.7% on mid-cap pairs.
Breakeven hours
The honest metric is time: how long must funding flow before costs are repaid?
breakeven = total costs / (spread per 8h) × 8 hours- 0.24% costs against a 0.53%/8h spread:
0.24 / 0.53 × 8 ≈ 3.6h— under one 8h settlement. Workable. - The same costs against a 0.05%/8h spread:
0.24 / 0.05 × 8 ≈ 38h— five 8h settlements just to reach zero, with flip risk compounding every interval.
The Spread page computes this as BREAKEVEN — funding to cover basis+fees, at your notional, live. If the number exceeds the horizon you actually believe the rate will hold, the trade is a donation to two exchanges.
Slippage scales, fees don’t
Fees are linear in size; slippage is not. Doubling notional on a thin book more than doubles the price impact, because your order walks deeper levels. The SLIPPAGE metric (effective @ notional) reprices as you change the size input — watch it, not the fee schedule, when deciding how big to go. The point where slippage overtakes fees is the practical size ceiling of the pair.
When maker legs make sense
Resting maker orders cuts the fee roughly in half or better and avoids crossing the spread — at the cost of uncertain fills. That trade-off is acceptable on the patient side of the position: entering the leg whose venue is not moving, or unwinding without urgency. It is a bad idea when the two legs must fill together — an unfilled maker leg is naked directional exposure; see Leg risk.