How Forex Rollover Interest Works

Forex rollover interest—sometimes called “swap” charges or credits—is the daily cost or gain of holding a currency position overnight. It arises from the interest rate differential between the two currencies in the pair; if one currency has a higher interest rate than the other, the trader pays or receives a small amount each day the position remains open.

The interest rate differential

At the heart of forex rollover is a simple principle: if two countries have different short-term interest rates, the currency of the higher-rate country is more valuable to borrow than the currency of the lower-rate country. When you hold a forex position overnight, you are effectively borrowing one currency and lending the other. The daily interest reflects that imbalance.

Consider a trader holding EUR/USD. They are long the euro (borrowing dollars at the USD rate) and short the dollar (lending euros at the EUR rate). If the Federal Reserve has set a 4.5% federal funds rate and the European Central Bank has set a 3.75% rate, the trader owes the difference daily. The U.S. interest rate is higher, so holding euros costs slightly more than holding dollars. Over a day, this difference is tiny—a fraction of a basis point per unit of currency—but it compounds over weeks and months of holding a position.

The direction reverses if rates move. If the ECB raises rates above the Fed’s rate, the EUR/USD pair flips: holding EUR overnight becomes profitable instead of costly.

How the rollover is calculated

Most brokers apply a simplified version of the true overnight lending rate. The calculation is typically:

Rollover = (Interest Rate Differential ÷ 365) × Position Size × Current Exchange Rate

If EUR/USD trades at 1.10, the EUR interest rate is 3.75%, the USD rate is 4.5%, and the position is 100,000 euros:

• Differential: 4.5% − 3.75% = 0.75% per year
• Daily amount: (0.75% ÷ 365) = 0.00205% per day
• In dollars: 100,000 × 1.10 × 0.000205 ≈ $22.50

The trader pays approximately $22.50 to hold 100,000 euros short-of-dollars overnight.

In practice, brokers add a small markup (the “spread”) to the true interbank rate. They borrow and lend at slightly different rates to monetize the rollover flow. A broker might offer you 0.65% on a 0.75% differential, pocketing the spread.

When you pay and when you earn

The simplest way to think about it: you earn rollover if the currency you are long has a higher interest rate than the currency you are short.

• Long GBP/USD (long pound, short dollar): You earn if the Bank of England rate exceeds the Fed rate.
• Short AUD/JPY (short Australian dollar, long Japanese yen): You earn because JPY rates are typically much lower than AUD rates; you profit from the differential.
• Long USD/BRL (long dollar, short Brazilian real): You pay if Brazilian real rates are higher (which is common); the high-yielding emerging currency costs you to hold short.

Many traders exploit this via the carry trade, deliberately holding pairs with large interest rate differentials to earn rollover income. A position held for weeks or months can generate meaningful returns from rollover alone if the differential is large enough—typically seen in emerging-market pairs or when there is an exceptional gap between central bank rates.

The weekend effect

Forex markets are closed over the weekend, but interest continues to accrue. Most brokers apply the weekend interest as a triple charge on Friday: three days of interest are deducted (or credited) when you hold a position through Friday into the next week. This is why Friday rollover is visibly larger on account statements than a normal weekday rollover.

If you are short a high-yielding currency like the Brazilian real and long a low-yielding currency like the Japanese yen (short USD/BRL, for example), the triple Friday rollover can be substantial. Conversely, if you are on the profitable side of the differential, the Friday triple credit is a bonus.

How rollover affects trading costs and strategy

For day traders, rollover is negligible. A position held for a few hours incurs no overnight charge.

For swing traders holding positions for days or weeks, rollover becomes a material cost or benefit. A position that breaks even on price might generate a small loss due to rollover, or be pushed into profit if rollover works in your favor.

For long-term carry traders, rollover can be the entire point. They may be indifferent to day-to-day price swings, focused solely on the daily interest income. In an extreme case, a carry trade can be profitable on rollover alone even if the exchange rate declines slightly over time.

Central bank policy and rollover changes

Rollover interest shifts whenever central banks change interest rates. A rate hike in one country changes the differential immediately. Traders often anticipate these changes, which can shift carry trade flows sharply around rate-decision meetings.

During periods of currency volatility or risk, the interest differential alone may not compensate for exchange rate losses. A high-yielding currency may fall as investors sell it, negating the rollover income. This is why carry trades can be risky in volatile markets: you earn daily interest but lose it all in a single adverse move if the exchange rate swings.

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