Hold a leveraged position past the daily rollover and an amount is debited or credited to your account. It reflects the interest-rate differential between the two currencies in the pair, adjusted for the cost of the financing itself. It happens quietly, once a day, and it accumulates.
Why direction changes the sign
When you are long a currency pair you are effectively holding the base currency and borrowing the quote currency. If the currency you hold pays a higher rate than the one you borrow, the differential can be credited to you. Reverse the position and the same differential is charged. The same trade idea can carry a cost or a small income depending only on which way round you take it.
Scale over a realistic hold
A spread of one pip is paid once. A financing charge is paid every night. On a six-week position that is roughly thirty debits, and triple on the day that carries the weekend. If the daily charge is a fifth of a pip, the total exceeds the spread several times over.
Check before entry, not after
The financing rate for every instrument is on the platform against the symbol. Read it while you are planning the trade.
Watch the weekend triple
Most instruments charge three days of financing on one weekday to cover the weekend. Know which day that is.
Include it in the target
A target that is profitable before financing and marginal after it is not a target, it is a hope.
Reconsider very long holds
If financing dominates the expected move, the trade may belong in a different instrument entirely.