Every foreign exchange position is two positions. Buy AUDJPY and you are long Australian dollars and short Japanese yen at the same time. Each side has an interest rate attached, set by its central bank and priced daily in the money market. If the currency you are long pays more than the one you are short, the difference accrues to you for as long as you hold. That difference is the carry.
Institutions run it in the forward market or through funding desks. Retail traders meet it as a line on the account statement: the overnight swap.
How the money actually reaches your account
Spot forex settles two business days forward. A position held past the daily rollover has to be rolled to the next value date, and the cost of that roll is the tom next rate, derived from the interest rate differential between the two currencies. Your broker applies that rate to your notional exposure and adds a markup, then credits or debits the result. The mechanics are covered in more depth in the guide to swap rates and rollover.
Two details change the arithmetic more than most people expect.
| Component | What it does to the carry |
|---|---|
| Policy rate differential | Sets the raw size of the credit or debit, and moves with every rate decision |
| Broker markup | Subtracted from the long leg and added to the short leg, so both directions can be negative |
| Triple swap day | One weekday carries three days of financing to cover weekend value dates |
| Notional, not margin | Swap is charged on full position size, so leverage multiplies it in both directions |
The markup is what kills most retail carry plans. When two policy rates sit close together, the differential can be smaller than the spread the broker takes, and the trader ends up paying to hold a position they believed would pay them. Read the published swap table for the instrument before the trade, not after the first rollover. Note too that swap free accounts, offered for religious reasons, remove the credit as well as the charge, so a carry approach and a swap free account are incompatible by design.
Why the trade works at all
Theory says it should not. Covered interest parity holds tightly in liquid markets: the forward price of a currency already reflects the rate gap, so hedging the exposure removes the profit. What carry traders take is the uncovered version, leaving the spot exposure open and betting that the higher yielding currency does not depreciate by the full differential.
Empirically it often does not, at least for long stretches. Economists have spent decades on the gap between what interest parity predicts and what spot rates actually do. The practical reading is straightforward: carry pays a risk premium, and you are being paid for holding a position that can lose more in one session than it earns in a quarter.
The currencies that show up in the trade
The pattern repeats across cycles. A low rate, deeply liquid currency becomes the funding leg, historically most often the Japanese yen and at times the Swiss franc. The long leg is a higher yielding currency, either a developed market commodity currency such as the Australian dollar, or an emerging market currency where the yield is far higher and so is the risk of a sudden devaluation or a capital control.
Which pairs are attractive changes whenever policy diverges, and that makes central bank policy the primary input rather than a background factor. A carry position is a bet on a rate gap staying open. Guidance that hints the gap will narrow can end the trade before a single rate has moved.
Carry has negative skew. The distribution of outcomes is many small positive days and a small number of very large negative ones. Any position sizing built on average daily volatility understates the tail, which is why leveraged carry positions are a high risk exposure regardless of how quiet the interest accrual looks.
Unwinds, and why they are violent
Carry positions concentrate in the same handful of pairs, held by the same kinds of accounts, financed with borrowed money. When something forces one group out, the exit routes are identical. Selling the long leg means buying back the funding currency, which strengthens it, which pushes the next trader closer to a margin call. That feedback loop is why funding currencies tend to appreciate sharply in stress episodes, and why the yen and the franc behave as safe haven flows even when nothing about their domestic economy has improved.
Two triggers dominate. A volatility shock, from any source, raises the cost of holding leveraged exposure and forces risk reduction. And a shift in the rate outlook for the funding currency, where a central bank that has been holding rates near zero signals a move higher. Neither needs to be large to start the sequence, because the sequence is driven by positioning rather than by the news itself.
Running carry as a retail trader
If you want to hold the exposure, treat the interest as a small tailwind on a directional position rather than the reason for the trade. The position still needs a stop placed on price structure, and the size still has to survive a gap through that stop, because leverage applies to the loss exactly as it applies to the accrual. Holding a position through a weekend adds gap risk that no swap credit compensates for.
Check three things before entering. What the broker actually pays on the long leg after markup, whether the pair's spread widens at rollover enough to matter for the size you hold, and what happens to the position if the funding currency appreciates by a few percent in a session. If the answer to the third question is a margin call, the trade is too big whatever the interest looks like on paper. Leveraged trading carries a high risk of loss, and the carry trade specifically is a strategy where the loss arrives faster than the income ever did.
"Carry looks like a savings account until the day it does not. If the interest is the only reason you are in the trade, you will be in it on exactly the wrong morning."
— Alex Onta, Executive Director, SINGUARD
Key Takeaways
- Retail carry arrives as the overnight swap, calculated on full notional and reduced by broker markup.
- When the rate gap is narrow, markup can make both directions of a pair pay negative swap.
- The trade is a bet that the rate gap stays open, so central bank guidance ends it before rates move.
- Crowded leveraged positioning makes unwinds self reinforcing, which is the source of the tail risk.
Frequently Asked Questions
How does a retail trader earn carry?
Through the overnight swap applied to positions held past the daily rollover. Holding the higher yielding currency long against a lower yielding one usually produces a swap credit, and the opposite direction produces a debit. The broker calculates it from the tom next market rate and applies its own markup on top.
Why is my swap negative on both sides of a pair?
Because the broker markup is applied to both the long and the short leg. When the underlying rate differential is small, the markup can be larger than the differential itself, leaving a debit whichever way you are positioned. Swap tables are published per instrument and are worth reading before planning any position held for weeks.
What causes a carry trade to unwind?
A shock to volatility or a shift in the rate outlook that makes the funding currency more expensive to be short. Because carry positions are crowded and leveraged, the exit is disorderly: stops and margin calls force the same direction at once, and months of accrued interest can be erased in days.