Swap is a particular amount per every roll-over position. Once the transaction is completed, you have earned credit in the currency you sell, and so must pay interest on it. At the same time you have placed bought currency on your deposit, which means you will earn interest on it.
Interest depends on the currency, and is taken into consideration when the position is carried over. If you sell currency with greater interest, you pay for the position carried over. If you bought a currency with greater interest, the broker will pay you for the position carried over.
A roll-over is usually processed automatically in the beginning of the day, prior to the valuation date.
The actual value date for Forex transactions is a second business day after the transaction. Therefore, when an open position is moved from Wednesday to Thursday, the value date is postponed until Monday because of the weekend, when the market is closed. It means that on Wednesday (midnight from Wednesday to Thursday) a triple Swap is charged for the weekend rollover.
The valid SWAP rates you can see in MT4 trading platform.
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