Hold a forex position one second past the daily rollover and the broker quietly adjusts your balance — sometimes in your favour, more often against it. That adjustment is the swap, and over a swing-trading month it can turn a positive edge into a break-even one without a single bad entry.
What a swap actually is
A swap (also called a rollover or overnight financing charge) is the interest paid or earned for keeping a leveraged position open past the broker’s end-of-day cutoff.
When you trade forex you are, mechanically, borrowing one currency to buy another. Each currency carries its own overnight interest rate. Hold the pair overnight and the broker settles the difference between those two rates on your position size — crediting your account if you’re on the right side of the differential, debiting it if you’re not. The number shows up on your platform as a per-lot cash amount, positive or negative, applied every night you stay in the trade.
It is not a fee the broker invents. It flows from the cost of carrying a leveraged, financed position across a day boundary. But brokers do add a markup to the raw interbank rate, so in practice the charge you pay is usually a little worse than the pure differential and the credit you earn a little thinner.
The interest-rate differential behind it
The direction and size of a swap come from the interest-rate differential between the two currencies in the pair.
- Buy a currency with a higher interest rate against one with a lower rate, and you tend to earn a positive swap.
- Buy the lower-rate currency against the higher-rate one, and you pay a negative swap.
This is the whole basis of the carry trade — holding high-yield-versus-low-yield pairs for months purely to collect the nightly credit. For most active traders, though, the differential matters in the other direction: it’s the slow drag on the pair you happen to be short when that pair pays negative on your side.
Two things make the number move: the size of the rate gap, and your position size. A wide differential on a large position compounds every single night, which is why the cost is invisible on a day trade and painfully visible on a two-week swing. Before you commit to holding size overnight, price the nightly figure against your expected move — the lot size calculator helps you see the position in cash terms so the swap isn’t an afterthought.
When rollover happens, and triple-swap Wednesday
Rollover fires at a fixed server time each day — commonly 5:00 PM New York time, though it varies by broker, so confirm the exact cutoff with yours. Cross that instant with an open position and one day’s swap is applied. Close before it and you pay nothing.
The wrinkle is triple-swap day. Spot forex settles two business days after the trade (T+2). To account for the weekend, when no interest accrues on the books, brokers roll three days of financing into a single night mid-week — usually Wednesday. So the swap you see on a Wednesday rollover is roughly three times a normal night’s charge or credit.
Two practical consequences:
- If you’re paying negative swap, a position held through Wednesday costs triple. Sometimes it’s cheaper to flatten before the cutoff and re-enter after.
- If you’re earning positive swap, Wednesday is your big collection night.
Some instruments shift their triple-swap day (metals and indices don’t always follow the Wednesday convention). Check the contract specs rather than assuming.
Swaps on forex vs futures vs CFDs
The overnight cost exists across products, but the mechanism differs — and that difference matters a lot for prop traders choosing a market.
| Product | Overnight cost mechanism | Where it shows up |
|---|---|---|
| Spot forex | Interest-rate differential, applied nightly, tripled mid-week | Direct swap debit/credit on the position |
| Futures | No nightly swap — carry is baked into the futures price and the roll between contract months | Contango/backwardation and the quarterly roll |
| CFDs | Daily financing charge on the notional, benchmark rate plus broker markup | Nightly financing line, almost always a cost |
Futures don’t charge a nightly swap at all — the cost of carry is priced into the contract and realised when you roll from an expiring contract to the next. That’s one reason many prop-firm traders on futures-focused platforms think about overnight cost less often; it’s structural rather than a nightly line item. If you trade a futures account through something like Tradovate or ProjectX, the roll schedule matters more than any swap figure. CFDs, by contrast, almost always charge financing every night on both long and short, because you’re paying to finance the full notional.
When overnight cost quietly erodes an edge
Here’s the honest failure mode: a strategy back-tested on close-to-close prices looks profitable, goes live, and bleeds. The gap is often swap.
Swap does the most damage when:
- You hold large size overnight relative to your target move.
- Your average hold spans several nights, so the charge compounds.
- You’re structurally on the negative-swap side of a pair (short the high-yielder).
- Your edge per trade is thin — a scalper’s few-pip target has no room to absorb a nightly debit.
Because swap lands after the position closes and never appears in your entry logic, it’s the kind of cost traders forget to log — which is exactly why it needs to be measured, not estimated. Shibiki’s auto-journaling captures the realised cost on every closed trade, swap included, so your recorded expectancy reflects what actually hit the account rather than the clean back-test. When the platform computes live edge health with a Wilson confidence interval, it’s working from net numbers — a strategy that only looks profitable before financing gets flagged before you scale it.
Prop firms differ on whether they even allow overnight holds, and some restrict weekend exposure entirely — confirm the specific policy with your firm, whether that’s The5ers, FundingPips, or another, before you build a strategy that leans on carrying positions.
Related: Lot size calculator · MT5 integration · The5ers