All open positions (at the end of a day of trading) must be rolled over to the next day. The interest rate differential between the two currencies will determine whether a credit or a debit is applied to the client’s account. This happens at midnight (meaning midnight wherever your broker is located – ex: you live in Dublin Ireland but your broker is located in Cyprus, midnight in Cyprus will be 10:00PM in your area!). It can be tripled between Wednesday night and Thursday morning. Check your broker’s website, they usually post the current applicable rollover rates. A few brokers actually don’t even charge rollover fees, but this should NOT be your only criterion for choosing a broker!).