Forex Swap and Carry Trade Mechanics

Every forex position held past 22:00 GMT rolls over, and rollover either pays you or charges you daily. Over weeks, swap can exceed the price move itself. Understanding the mechanism turns an invisible cost into an explicit edge — or a reason not to hold.

What Swap Is

Swap is the interest rate differential between the two currencies in a pair, applied daily at rollover (typically 22:00 GMT / 17:00 ET). Long the higher-yielding currency, you receive swap; long the lower-yielding, you pay it. Wednesday rollover credits or debits triple (settlement for the weekend). Formula approximation:

Swap (per standard lot, daily) ≈ (Quote rate − Base rate) ÷ 365 × contract size × exchange rate.

A long AUD/JPY position when AUD pays 4.35% and JPY pays 0.10% earns roughly (0.0435 − 0.0010) ÷ 365 × 100,000 × 0.0067 ≈ ¥78/day per standard lot — positive carry. A long EUR/CHF position when both rates are similar earns near zero.

The Carry Trade

The carry trade buys the high-yield currency, sells the low-yield currency, and collects the differential. AUD/JPY, NZD/JPY, MXN/JPY, TRY/JPY are classic pairs. Carry returns are steady and small — annualized 2-8% on majors, 10-30% on exotics — but the risk is sharp drawdowns when the high-yield currency depreciates faster than carry accrues. The 2008 unwind saw AUD/JPY drop 35% in three months; the 2022 rate-hike cycle saw JPY crosses swing 15%.

Carry Trade Rules

1. Trade only pairs with a clear rate differential (≥2%). Below that, swap noise exceeds the edge.
2. Size for the drawdown, not the carry. Risk per position 0.5-1% of equity, not 5%, because carry trades trend against you for weeks.
3. Use technical filters. Enter after a correction in the direction of the carry (buy AUD/JPY on a pullback, not after a 10-day rally).
4. Avoid calendar risk. Cut or hedge before central bank meetings — a single rate reversal erases months of carry.
5. Watch funding stress. When JPY strengthens across the board, unwinds have started — exit, do not average down.

Negative Swap: The Hidden Drag

Most retail brokers widen swap rates 20-50% from interbank, so you pay more and earn less than the theoretical rate. A long EUR/USD position paying 0.1% theoretical can cost -0.5% annually at retail. Over a 6-month swing, that is 2.5% — enough to flip a marginal edge negative.

Practical Checks

• Read the broker's swap table for every pair you hold overnight. Multiply by your lot size.
• For holds over one week, compute cumulative swap and add it to your break-even. If swap is 40% of your target profit, the trade is no longer what you sized.
• Use swap-aware strategy: day traders ignore it; swing traders model it; carry traders exploit it.