The essentials
Perpetual futures do not have a fixed expiry. Periodic funding payments between long and short positions help align the contract price with the underlying spot index.
What to consider
A positive funding rate usually means longs pay shorts. Rates can change, and a seemingly profitable basis trade still carries execution, margin and liquidation risk.
Put it into practice
Calculate funding, trading fees and adverse price moves together. Monitor margin independently on both legs and do not treat historical funding as guaranteed income.