Overnight financing on a cash index position

This is the cost people discover in a statement rather than in advance, and on a position held for weeks it routinely exceeds the spread they shopped around for.

Why there is a charge at all

A cash index position gives you the exposure of the whole contract while you have posted a fraction of its value. The difference is financed, and financing costs money.

So the charge is not a fee the broker invented. It is interest on the part of the position you did not fund, plus the broker's markup on that rate.

It has a direction

The long side pays: you are financing an asset position. The short side receives the reference rate and pays the markup, so whether a short earns or costs depends on where rates are and how large the markup is.

When reference rates are near zero, shorts typically pay too, because the markup exceeds what is credited. When rates are high, a short position can genuinely earn.

Counting the nights

It accrues per night held, not per day traded. A position opened and closed inside a session pays none of it, which is the entire reason day traders and swing traders shop for different things.

Weekends are charged, though brokers differ on how: some apply three nights on a Friday, others charge seven nights a week at a lower rate. Read yours rather than assuming - and count charged nights, not calendar days, which is the same discipline the FX track's swap lesson teaches.

The comparison worth making

Set that total against the spread from lesson 2 and the ranking of the two costs flips somewhere in the first fortnight. On this example it flips almost immediately.

Which is the module's central point, and lesson 8 turns it into a number you can calculate before opening the position rather than discover after closing it.