What Is a Forex Swap Fee? How It's Calculated

You leave a position open overnight and wake up to find your account balance a little lighter, even though the price hasn't moved at all. That's the swap fee at work.

A swap fee (also called rollover) is the interest charged or credited when you hold a forex position overnight, based on the interest rate differential between the two currencies in the pair. It can be positive (you earn) or negative (you pay), depending on the direction of your trade and which pair you're holding.

This article doesn't reference any single broker's actual swap table, because real numbers change daily and vary by provider. Every figure here is illustrative, meant to explain the mechanism, not a value you should use to calculate real costs. Nothing here is personalized investment advice. Check your own platform's live swap table before trading.

What causes a swap fee

Forex trades currency pairs, so every position you open means holding two currencies at once, buying one and selling the other.

Each currency has its own policy interest rate, set by that country's central bank, the US dollar by the Federal Reserve, the Japanese yen by the Bank of Japan. The rate differential between the two currencies in a pair is the actual source of the swap.

In theory, if you buy the higher-yielding currency and sell the lower-yielding one, you should collect that rate differential. Do it the other way around, and you pay it instead.

This mechanism is known institutionally as a currency carry trade, a strategy that's been used in FX markets for decades. Retail brokers translate that interest cost into a daily swap figure, then add their own markup on top, which is why the swap number you see on your platform rarely matches the pure policy rate differential.

Most platforms apply the swap charge at midnight server time (commonly GMT or GMT+2/+3, depending on the broker). One thing that trips up newer traders: Wednesday night. Many platforms charge triple swap that night, to account for the weekend when the market is closed but currency settlement still runs on a 7-day calendar, not a 5-day one.

Swap long vs. swap short

Every pair carries two swap values, one for long (buy), one for short (sell), and the two are rarely mirror images of each other.

Take an illustrative example on AUD/JPY (Australian dollar against Japanese yen), a classic pair with a clear rate gap between the two currencies.

Notice the two numbers aren't simply mirror opposites. A lot of traders assume if long earns +0.85, short should cost exactly -0.85. In practice almost no broker sets it up that way, because this is exactly where broker markup gets layered into both sides at once. More on why below.

How to calculate a swap fee, step by step

The basic formula most brokers use looks like this:

Swap (in account currency) = (swap points shown on platform) × (lot size) × (nights held)

Let's run illustrative numbers. Say you open a long EUR/USD position at 1 standard lot (100,000 units), and your platform shows the long swap at -3.20 points per lot per night.

Step 1. Figure out what one point is worth for this pair. For EUR/USD at 1 standard lot, one point is typically worth about $1 USD (this varies by pair and lot size, always check your own platform).

Step 2. Multiply the swap points by the point value.
-3.20 × $1 = -$3.20 per night

Step 3. Multiply by nights held. Say you hold for 5 nights (excluding a Wednesday triple-swap night for now).
-3.20 × 5 = -$16.00

Step 4. If one of those five nights is a Wednesday, replace that night's charge with the triple rate.
(-3.20 × 4) + (-3.20 × 3) = -$12.80 + -$9.60 = -$22.40

This is an estimate only. Real market pricing can shift the swap points slightly night to night, especially right after a central bank rate announcement.

Why swap fees differ between brokers on the exact same pair

This is the part almost every competing page skips, because each one is broker-owned. They all eventually point back to their own platform as the trustworthy example.

The pure interest rate differential is only the starting point. What each broker does from there:

1. Adds its own markup. This is a separate revenue line for the broker, alongside spread and commission. The higher the markup, the further the displayed swap drifts from the actual central bank rate differential.
2. Sources liquidity from a different provider. Brokers don't lend currency to each other directly, they price off their own liquidity provider (LP), and each LP has its own overnight funding cost.
3. Runs a different account model. ECN accounts that charge commission separately tend to keep swap closer to the real cost. Standard accounts with no separate commission often bury markup into both spread and swap at once.

In plain terms, swap isn't a number the market fixes for everyone, it's a number each broker sets on top of the same base. Two coffee shops buying beans from the same source can still price the final cup differently.

Why this matters for cost over time

If you scalp or day trade, closing every position before the market closes, swap barely touches you.

But if you hold overnight often, especially swing or position trading where some trades run for weeks or months, a markup that looks small per night can quietly eat more of your profit than expected.

Picture a position held 30 nights. At -$3.20 per night from the example above, that's nearly $100 over the month, and the pair may not have moved at all. This is the part newer traders tend to miss, they're watching price and forgetting a cost with nothing to do with price is running the whole time.

There's a second thing leveraged traders overlook: swap is calculated on the position's full notional value, not the margin you actually posted. Open 1 lot at roughly $100,000 notional using 100:1 leverage, and you might post only about $1,000 in margin. A swap charge that looks small in dollar terms, say -$8 to -$9 a night, can work out to nearly 1% of your actual margin per night once you compare it that way. The higher your leverage, the higher swap's real cost relative to the capital you actually have at risk, even when the dollar figure looks unremarkable.

Swap-free (Islamic) accounts, and whether they're a real substitute

A swap-free account, often called an Islamic account, charges or credits no swap at all. It exists to comply with the Riba principle in Islamic finance, which prohibits paying or receiving interest.

Worth knowing upfront: brokers don't actually offer this for free, since the underlying overnight funding cost is still real. What most brokers do instead:

• Charge a flat daily administration fee in place of swap, which can end up more expensive than ordinary swap on a long enough hold
• Widen the spread slightly to make up the difference
• Restrict the account to certain pairs or account types only

So a swap-free account isn't free in every sense, the name suggests. It just moves the cost from nightly interest into a different fee structure. If you're a day trader who closes every position anyway, this type of account may not do anything for you, since you were never hitting swap in the first place.

Checklist: is your broker's swap fair

Before deciding your broker's swap is overpriced, run through this:

1. Check whether the broker publishes a detailed swap table. It should be visible on the website or directly in the trading platform, not something you have to ask support for.
2. Compare the long/short sign against what it should logically be. If the currency you're buying has a higher rate than the one you're selling, long should tend positive, or at least less negative than short. If both sides are negative on a pair with a clear rate gap, that's a signal of unusually high markup.
3. Compare the same pair across at least 2 to 3 brokers, same day. If the numbers differ by more than 2 to 3 times, some broker's markup is likely excessive.
4. Read the triple-swap-day policy. Confirm it actually lands on Wednesday night, and check for adjustments around bank holidays, which some brokers announce in advance.
5. If you're holding long-term, calculate the cumulative swap cost upfront, before opening the position, not after closing it.

Who actually feels swap the most

FAQ

Is swap the same as rollover?
Yes, the two terms are interchangeable. Both describe the same process, renewing an overnight position while charging the interest differential.

Do I get charged swap if I open and close on the same day?
Generally no. Swap only applies to positions still open at the platform's daily cutoff (usually midnight server time). Close before that and you avoid it entirely.

Why do some pairs show no swap at all?
Usually because the two countries' policy rates are close enough that the differential rounds to zero or near-zero. It doesn't mean the swap mechanism doesn't apply to that pair.

How often does swap change?
It can change daily, especially after a central bank rate decision, or during periods of high volatility when LP funding costs shift. Always check the current table before opening a long-term position rather than relying on a number you saw once.

Bottom line

A swap fee isn't some arbitrary charge a broker invented. It comes from a real interest rate differential between the two currencies you're trading, plus a markup each broker sets independently, which is why the number is never identical across two platforms.

If you scalp or day trade, this barely touches you. If you hold overnight often, understanding the mechanism and checking the swap table before every trade is a basic step worth not skipping, the same way it's worth verifying a broker's license before depositing real money or understanding how Introducing Broker (IB) commission structures can quietly sit inside your overall trading costs.

If your goal is minimizing swap cost specifically, see our roundup of brokers with swap-free accounts or low swap rates for a comparison.

This article is for general education only, not personalized investment advice. Forex trading carries significant risk and is not regulated by any authority in Thailand. Traders should research further and assess their own risk before making decisions.