Every currency has an interest rate attached to it, set largely by its central bank. Because FX trades one currency against another, holding a pair means you are effectively borrowing one currency and lending the other. The difference between the two rates is the foundation of the carry trade. It is one of the oldest ideas in currency markets, and one of the most misunderstood by retail traders.
The basic mechanics
Suppose, purely for illustration, that Currency A pays 5 percent and Currency B pays 1 percent. A trader who buys A against B is long the higher yielder and short the lower yielder. Holding that position overnight earns the differential, roughly 4 percent per year, before costs. Conversely, holding the opposite position pays it. That overnight credit or debit is called swap, rollover or financing, depending on the broker.
What retail swap actually looks like
The headline interest differential is not what you receive. Brokers add a markup to the rate they pass on, so a long position in the higher yielder may earn less than the theoretical differential, and the opposite position may cost more than it. In some cases both directions show a debit. Swap is usually applied at the daily rollover, and many brokers apply triple swap on one day of the week to account for the weekend settlement cycle. Check your broker's published swap table and the rollover day before holding anything over several days. See also our guide to broker due diligence, which includes reading fee schedules.
Leverage changes the arithmetic
A 4 percent annual differential is modest compared with typical daily movement in many pairs. The trade becomes attractive to some people only when leverage multiplies it. But leverage multiplies the exchange-rate movement just as much, and exchange-rate movement is normally far larger than the carry. A 3 percent adverse move in the pair can wipe out nearly a year of carry on an unleveraged position, and many times that on a leveraged one. For the mechanics of margin and leverage, read lots, leverage and margin explained.
Why carry tends to work, until it does not
Historically, high-yielding currencies have often held up better than theory would suggest, which has attracted capital to carry strategies over long stretches. The reason is not free money; it is usually seen as compensation for bearing risk. Carry returns tend to arrive slowly during calm markets with low volatility, and then reverse abruptly when volatility spikes and investors rush to unwind positions funded in low-yielding currencies. The pattern is sometimes described as "going up the stairs and down the elevator."
Several episodes in market history illustrate the pattern: periods of calm in which funding currencies weakened steadily, followed by short, violent reversals that erased months of accumulated carry in days. We will not cite precise figures here, but any long price chart of a classic funding-currency pair will show this shape.
What drives the differential
- Policy rates. Expectations for central bank decisions matter more than today's rate. If the market expects the high-yielder to cut, the differential may shrink before it does. See how central banks move FX.
- Inflation. Persistent inflation pushes rate expectations higher; see how inflation data moves currencies.
- Risk appetite. Funding-currency demand rises in stress, which is why carry positions suffer in risk-off episodes.
Common mistakes
- Treating swap as the whole return. The price move dominates. A positive swap on a losing trade is still a losing trade.
- Ignoring the stop. Because carry feels like income, traders hold through drawdowns that would otherwise trigger a plan. Define the invalidation level first.
- Oversizing because the trade pays you to wait. Size by the stop distance and your acceptable loss, not by the daily credit. See position sizing and risk per trade.
- Forgetting event risk. Rate decisions, intervention warnings and emergency policy shifts can move a pair by hundreds of pips in minutes.
- Ignoring correlation. Several carry positions can all be the same risk-on bet. See currency correlation explained.
A sober framework for studying carry
If you want to explore carry, treat it as a research question, not a shortcut:
- Find the current policy rates for both currencies from the central banks themselves, and compare them with your broker's quoted swap.
- Compute the annual swap as a percentage of the pair's price and compare it with the pair's typical monthly range, using something like ATR.
- Ask how many pips of adverse movement it takes to cancel a month of swap. If the answer is small, carry is a minor factor in the trade.
- Note the position in your journal including cumulative swap, so you can see honestly what the financing contributed.
Tax and reporting note
Swap credits and debits are part of your trading result in most jurisdictions, and your broker's statement will show them separately. Keep those statements for your records.
The bottom line
Carry is a real feature of FX, but it is a modest, steady payment attached to a volatile asset. It rewards patience in calm markets and punishes complacency in turbulent ones. Understand it as one input among several, not as a standalone strategy with guaranteed income.
This article is educational and not investment advice. Leveraged FX trading carries a high risk of loss. Rates used in examples are illustrative.