Basics
The interest you pay or earn for holding a forex or CFD position past the daily cut-off.
Holding a forex position past 17:00 New York time (the daily rollover) means paying or receiving interest, called swap. It comes from the interest rate difference between the two currencies, plus the broker's markup, so it can be a cost on both sides. On Wednesdays most brokers charge three days' swap at once, to cover the weekend, because spot forex settles two days later. Index and commodity CFDs often take the triple charge on Friday instead.
Spreads also widen around the rollover, often sharply for a few minutes, which can trigger tight stops.
For education only, not financial advice.