What is swap?
Swap, also called rollover, is the interest you pay or earn for keeping a position open past the daily rollover. It comes from the interest rate difference between the two currencies in the pair, plus the broker's markup. That is why one side of a pair can pay you while the other side charges you.
Where to find your swap rates
In MT4 or MT5, right-click the symbol in Market Watch and open Specification. You will see Swap long (for buys) and Swap short (for sells), usually in points per lot. Enter those two numbers into the calculator.
Swap = Swap rate (points) × Point size × Contract size × Lots × Nights
Triple swap Wednesday
Forex trades settle two business days after they open. A position held through Wednesday's rollover settles after the weekend, so most brokers charge or pay three nights of swap that night. Some brokers do this on Friday for metals and indices, so check yours.
Swap example
Buy 1 lot of EURUSD with a swap long of −7.5 points. One night costs 7.5 × 0.00001 × 100,000 = $7.50. Held from Monday to Thursday, the trade crosses three rollovers, and Wednesday counts three times, so you pay for 5 nights: $37.50. In the calculator, enter 3 nights and tick the Wednesday box.
Swap-free accounts
Many brokers offer swap-free accounts, often called Islamic accounts. Some of them charge a fixed holding fee instead of swap after a few days, so read the account terms.