How FX Rollovers Are Calculated on Open Positions

The FX rollover is the overnight financing charge (or credit) applied to a foreign exchange position held past the settlement date. It flows directly from the interest-rate differential between the two currencies in a pair and is quoted in swap points that traders convert to a daily P&L impact.

Why Rollovers Exist: Interest Parity

When you hold an open foreign exchange position overnight, you are in essence borrowing one currency and lending another. If you buy EUR/USD, you simultaneously borrow US dollars and lend euros. Since the interest rates on those two currencies are almost never equal, one side of the trade accrues interest and the other side incurs a cost.

A FX rollover compensates (or charges) for that interest differential. It is the daily funding cost of maintaining the position. The calculation rests on the covered interest rate parity principle: the forward exchange rate should reflect the spot rate plus the interest-rate difference. When positions roll over, the broker passes through this interest cost or benefit.

The Core Formula

The rollover charge (or credit) per unit is straightforward in concept:

Rollover (pips) = (Interest rate differential / 365) × Position size in base units

In practice, it is quoted in swap points—basis points in the fourth decimal place (0.0001). A position rolling overnight at +5 swap points means you earn 5 pips per 100,000 units of the base currency.

Worked example:

• Currency pair: EUR/USD
• Spot price: 1.0800
• EUR annual interest rate: 4.0%
• USD annual interest rate: 5.5%
• Interest-rate differential: –1.5% (unfavorable for the EUR buyer)

The trader who buys EUR/USD borrows USD at 5.5% and lends EUR at 4.0%, netting a –1.5% annual cost. Over one day:

Rollover = –1.5% ÷ 365 = –0.00411% per day

Per 100,000 EUR (one standard lot):
Rollover cost = 100,000 × 1.0800 × (–0.00411%) ≈ –$4.44 USD per night

Brokers quote this as swap points. A –41 swap point position reflects the same cost (41 pips at the fourth decimal place).

Swap Points and the Bid-Ask Spread

Brokers do not pass through the pure interest-rate differential. They widen the spread. A typical retail forex broker might quote:

• Buy (long) EUR/USD: +3 swap points
• Sell (short) EUR/USD: –8 swap points

The difference (11 points spread) is the broker’s profit on funding. The true midpoint swap might be –2.5 points, but the broker quotes +3 for longs and –8 for shorts, pocketing 5–6 points per lot per night.

Friday and Holiday Adjustments

Most brokers triple the rollover charge on Friday (or the last business day before a weekend or holiday) because the position will sit over two days (Saturday and Sunday, when no trading occurs, but interest still accrues). This is sometimes called a weekend rollover or 3-day rollover.

Example: If a standard rollover is –5 points, a Friday rollover might be –15 points to account for the two-day gap. This avoids the arbitrage opportunity of holding a position through Friday at the same daily rate.

Calculation by Broker: Points to Pips to Currency

Different brokers automate this differently, but the chain is always:

1. Calculate the interest-rate differential (e.g., –1.5% annually)
2. Annualize the overnight rate (–1.5% ÷ 365 = –0.0041% per day)
3. Convert to swap points (depends on the currency pair and the exchange rate)
4. Add the broker spread (typically 2–5 pips wide)
5. Quote to the trader (±N points per lot per night)
6. Convert to account currency (multiply by the position size and the exchange rate to settle in the trader’s base currency)

For a 1 lot (100,000 units) of EUR/USD at 1.0800, a swap point translates to approximately 1 USD per lot per night. This makes the math transparent: if the swap is –5 points, the cost is roughly –$5 per lot per night.

Why Rollovers Matter: Carry Trade Signals

The rollover cost (or benefit) is a standing source of P&L in long-term forex trades. Traders exploit positive rollover (a credit) by holding high-yielding currency pairs overnight. The classic carry trade buys a high-interest-rate currency (e.g., the Australian dollar or Brazilian real) financed by shorting a low-rate currency (e.g., the Japanese yen or US dollar), collecting the daily interest differential.

Conversely, traders avoid or short pairs with large negative rollover. If EUR/USD rollover is consistently –5 to –10 points per night, a long position hemorrhages money just from overnight funding. Over a year, that adds up: –7 points × 250 trading days × 100,000 units × ~$1 per point ≈ –$17,500 per standard lot.

Central Bank Interest Rate Moves and Rollover Shifts

Rollovers shift whenever central banks change interest rates. If the Federal Reserve raises rates and the ECB keeps steady, the EUR/USD rollover swings in the USD’s favor (more negative for EUR buyers). Savvy traders monitor Fed and ECB schedules, because large rate divergences can make or break the profitability of a carry position.

During financial crises or periods of rate cuts, rollovers can flip dramatically. In 2020, when the Fed cut rates to near zero, long USD positions stopped earning carry; short USD positions (longs in other currencies) became more attractive on rollover alone.

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