Think of a parking garage that charges a fee each night. Take your car out before 5 pm and you pay nothing. Stay past 5 pm and the night fee is charged. Your trade is the car, and the fee is the swap. Drag the car to see it.

Each trading day has a cut-off, called the rollover, at about 5 pm New York time. Hold a trade past it and a small fee applies. Close before it and you pay nothing.

The fee is called the swap. It can cost you or pay you, depending on whether you are buying or selling. For example, holding a 0.10 lot buy of gold might cost $0.60 a night, while a sell might earn $0.20. Your broker lists the rates, so check them.

A swap is charged for each night you hold. One night a week counts triple to cover the weekend. A buy held all week in this example costs about $3.60. Figures are illustrative.

Swap is the fee for holding a trade overnight. Day traders who close before the rollover rarely pay it. Swing and position traders feel it most.