I just noticed that many people still don't understand what a swap is, even though it’s actually eating into their profits every day.

Honestly, a swap is the fee for holding an overnight position. It may seem minor, but if you trade and hold positions for a week or a month, it can become a significant hidden cost.

Where does it come from? Essentially, it relates to the interest rate differential. When you buy EUR/USD, you're actually "borrowing" USD and "buying" EUR. Each currency has its own interest rate. If EUR offers 4% per year but USD offers 5% per year, you have to pay the interest difference.

But here’s where brokers come in. They act as intermediaries in this borrowing process, adding their "handling fee" on top. As a result, even though theoretically you might receive a positive swap, in reality, it often turns out negative.

What many people overlook is the 3-Day Swap. The Forex market closes on Saturday and Sunday, but interest continues to accrue. So, brokers have to consolidate the swap for Saturday and Sunday into one trading day—usually Wednesday night. When you hold a position overnight on Wednesday, you’re charged a triple swap, not just one.

Checking the swap rate is straightforward. If you use MT4/MT5, go to Market Watch, right-click on the asset, and select Specification. You’ll see the Swap Long and Swap Short. If you’re on other platforms like Mitrade, it’s clearly displayed as an overnight fee percentage.

Let’s do a calculation. Suppose you buy 1 lot of EUR/USD at 1.0900, and the Swap Long is -0.008% per night.
Position value = 1 lot × 100,000 × 1.0900 = 109,000 USD
Swap fee = 109,000 × (-0.008 / 100) = -8.72 USD per night

It doesn’t seem like much, but if you’re using 1:100 leverage, your margin is only 1,090 USD. An 8.72 USD swap fee per night is 0.8% of your margin daily. If the market moves sideways for 10 days, you’ve lost 8% of your margin.

This is why swap is important—it’s not just a minor detail.

There’s also the opportunity for carry trade: trading to buy currency pairs that offer positive swaps, like buying AUD/JPY. If the swap long is positive, you earn money every night you hold the position. The risk is currency fluctuation; if AUD/JPY drops sharply, the loss could outweigh the accumulated swap profits.

If you want to avoid this, consider swap-free or Islamic accounts. They don’t charge any swap fees, regardless of how long you hold the position. The trade-off might be a slightly wider spread.

In summary, if you’re a short-term trader, swaps have little impact. But if you’re a swing trader or position trader, you need to choose to trade only the side with a positive swap or use a swap-free account, or else the swap costs will eat into your profits.