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Three days. That is how long one trader in London held a single EUR/USD position last spring, and it cost him roughly £41 in charges that never appeared on his chart. No stop-out. No spread widening. No slippage. Just a small debit applied at 5pm New York, quietly, while he was asleep.
That debit is the forex swap rate, and for anyone who holds a position past the daily rollover it is often the largest line item in the trade's profit and loss that nobody bothered to plan for.
Spot forex settles in two business days. If you want to keep a position open longer than that, your broker has to roll the settlement forward, borrowing one currency and lending the other to do it. Every roll has a price. That price is the swap.
Underneath it sits a simple idea: every currency pair is also an interest rate trade. Buy AUD/JPY and you are long Australian dollars, which earn a policy rate, and short Japanese yen, which earn something close to zero. The gap between those two rates is the carry, and the swap rate is how that carry gets handed to you or taken off you, one night at a time.
You will see it quoted two ways. Some brokers list it in pips or swap points per lot per night. Others show it in the account currency. Either way there are two numbers, one for longs and one for shorts, and they rarely mirror each other.
Take AUD/JPY at 97.00 with one standard lot. You are long 100,000 Australian dollars and short roughly 9,700,000 yen. Call the overnight AUD rate 4.35% and the JPY rate 0.10%. The differential is 4.25% a year, which on 100,000 AUD works out at 4,250 AUD annually, or about 11.64 AUD a night. At 97.00 that is roughly 1,129 yen, and one pip on a standard lot of AUD/JPY is 1,000 yen.
So the raw carry is a little over one pip a night in your favour. Brokers quote something slightly less, and the gap is where the real story lives.
Now look at it against margin. The notional is about 65,000 US dollars. At 3% margin you have posted roughly 1,950 dollars. A credit of 7.60 dollars a night against 1,950 dollars of collateral is about 0.39% per day, which annualises to something north of 140%. That figure is why the carry trade has seduced so many people.
The interbank differential above is the theoretical version. What lands in your account is that figure minus a markup, and the markup varies wildly from one broker to the next. Some run 0.1% annualised. Others quietly charge several times that. On a pair with a 4% differential the difference is invisible to a day trader and genuinely expensive to someone holding a position for six weeks.
Forward points are baked in too, and they move. Swap is priced off short-term funding markets rather than policy rates alone, so it drifts around month-end balance sheet dates and quarter-end squeezes. When liquidity thins and there is nobody on the other side of the market, retail swap spreads widen with it.
The principle is the same one that governs fills. What you receive is not the theoretical price. If you have ever wondered why your fill isn't the price you clicked, the distance between interbank swap and retail swap comes from exactly the same place: the cost of somebody standing between you and the market.
Because spot settles T+2, a Wednesday roll pushes settlement out to Friday, and the broker has to cover the weekend in between. Most brokers respond with a triple swap that night to account for Saturday and Sunday.
Work through the calendar. A position opened Sunday evening and closed on Thursday rolls four times, but it collects or pays six nights of swap, because Wednesday counts three. On a pair charging one pip a night, that is a six-pip swing for a four-night hold, which is more than most people pay in spread on the whole trade.
Public holidays shift things as well. If Monday is a US holiday, the triple often moves to Thursday for dollar pairs. Brokers publish rollover calendars for precisely this reason, and it is worth a look before any hold that spans a long weekend.
The classic carry trade buys high yielders against low yielders and simply sits there collecting the swap. That 140% annualised return on margin makes it look like free money.
Then it unwinds. In early August 2024 the yen carry trade cracked: USD/JPY slid from near 161 to around 142 in a matter of weeks, much of it in a handful of brutal sessions. A position earning 1.1 pips a night surrendered months of accumulated carry in an hour. Volatility does not care how much carry you have banked.
Carry is compensation for taking a risk, not a substitute for one. The pairs that pay the most swap are usually the ones that gap the hardest.
A scalper who is flat within the hour can ignore swap entirely. A swing trader holding three to eight days cannot. The moment your average hold crosses the daily roll, swap becomes a fixed cost sitting right next to commission and spread, and it belongs in your backtest rather than your surprises.
Islamic and swap-free accounts exist for legitimate reasons, but many replace the swap with an administration fee that starts after a set number of days, or widen the spread to compensate. Read the terms carefully. A fee that begins on day six is designed for people who intend to hold for six weeks.
There is a specific kind of loss that swap causes: refusing to close a losing position because it is paying you to stay. The accrual feels like progress. It is not. A trade sitting 80 pips underwater that earns a pip a night for a month is still a trade underwater by 50 pips, and you carried the exposure the entire time.
If you recognise the habit of breaking your own trading rules, this is one of the more expensive ways it shows up. Set the exit before the entry. If the thesis was a two-day move and two days have passed, the carry is not a reason to stay.
Run the numbers on a realistic hold. Twenty nights at one pip a night is 20 pips of cost. Your spread might be 1.2 pips and your target 60 pips. Suddenly swap is a third of your edge, and it is charged with absolute certainty regardless of whether the trade works.
That reframes the decision. On a two-day trade, ignore swap. On a three-week position, treat it as a position size question: either shrink the size, shorten the hold, or accept that you need a bigger move to come out ahead. And if the pair pays you rather than charges you, ask what risk you are being paid to carry, because the market is rarely generous by accident.
The number is published, it is knowable in advance, and it compounds quietly every night at 5pm New York. Most traders never look it up.
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