Yesterday, I chatted with a fellow trader. He said that one of the most overlooked costs is the swap fee—which is actually very important if you like to hold positions overnight. So I want to share a clear understanding of this topic.

Simply put, a swap is the interest that accrues from holding an order across days. When you trade currency pairs, such as EUR/USD, you are actually borrowing one currency to buy another. If you Buy EUR/USD, you are buying EUR and simultaneously borrowing USD. If you Sell EUR/USD, you are borrowing EUR and buying USD instead.

Each currency has its own interest rate, set by central banks—for example, USD by the FED or EUR by the ECB. When you borrow a currency, you have to pay interest on it, and when you hold a currency, you should receive interest from it. A swap is simply the net difference between these two interest legs.

For example, if EUR is 4.0% per year and USD is 5.0% per year, when you Buy EUR/USD you receive EUR at 4.0% but you must pay USD at 5.0%. The difference is -1.0%, meaning you have to pay swap in that direction. Meanwhile, if you Sell EUR/USD, you pay EUR at 4.0% but receive USD at 5.0%. The difference is +1.0%, so you receive swap instead.

In reality, brokers often add their own management fees. So even though, in theory, you should receive a positive swap, what you actually receive may be much less—or it may even turn negative on both sides. This is why Swap Long and Swap Short are not exactly the same.

What beginner traders often miss is the 3-Day Swap: the day when you are charged triple the swap fee. This usually happens on Wednesday night, because the Forex market closes on Saturday and Sunday, but interest keeps accruing. Brokers have to roll up and collect the weekend swap fees into the trading day.

Checking the swap before opening an order is important. On platforms like MT4 or MT5, go to Market Watch, right-click the asset, and select Specification. You will see Swap Long and Swap Short displayed. Some platforms show them as a percentage per night, which makes calculation easier.

For calculation, if the broker shows swap as a percentage, the formula is: total position value multiplied by the swap percentage. For example, if you Buy 1 Lot EUR/USD at 1.0900, the total value is 109,000 USD. If swap is -0.008% per night, then the calculation is 109,000 multiplied by -0.008 divided by 100, which equals -8.72 USD per night.

The important thing to know is that swap is calculated based on the full position value, not on the Margin you put up. If you use 1:100 leverage and only post Margin of 1,090 USD, you still pay 8.72 USD per night. That is 0.8% of your margin per night. When the market doesn’t move at all, this is why swap can be a scary hidden cost.

But swap isn’t only about risk—it also creates opportunities for certain traders. Carry Trade is a strategy that directly takes advantage of Positive Swap. The idea is to borrow a low-interest currency, such as JPY, and use it to Buy a high-interest currency, such as AUD, so you receive positive swap every day. For example, Buy AUD/JPY: if the Swap Long rate is positive, you earn money every night you hold the order. The risk is the exchange rate—if AUD/JPY falls sharply, the exchange loss could outweigh the accumulated swap profit.

Another interesting option is a Swap-Free account, sometimes referred to as an Islamic account, where no swap fee is charged no matter how long you hold the order. This is ideal for Swing Traders or Position Traders who want to hold positions for weeks or months without worrying about swap eating into their profits.

In summary, swap is something you need to consider starting from the moment you plan your trades—not just a small, “annoying” fee. For very short-term traders it may have little impact, but for people holding for months or years, it can be a massive factor. Choosing a broker that is transparent about fees and a platform that clearly displays information will help you plan your trades more carefully, without hidden costs surprising you later.