Hold a EURUSD position open at 5 PM New York time, even by thirty seconds, and the broker charges or credits an overnight financing fee most traders have never actually read the fine print on. On a small position it is a few cents. On a position sized properly against a real stop, meaning a meaningful chunk of a $10,000 account, it can run several dollars a night, and it compounds every single day the trade stays open. Day traders who close everything before the New York day ends never pay it. Anyone who leaves a position open past that line, even accidentally, does.
Why 5 PM New York is the line
Forex has no single daily close the way index or equity markets do, but the industry treats 5 PM New York time as the end of the trading day for settlement purposes, because that is roughly when New York liquidity has thinned out and the next session, Wellington, then Tokyo, is about to begin. Any position still open at that moment gets marked for an overnight rollover: the broker effectively closes and reopens the position at the prevailing rate, and the interest rate differential between the two currencies in the pair gets applied as a credit or a charge.
How the swap number gets calculated
Every currency has an associated overnight interest rate, and swap is a function of the difference between the two currencies in a pair. Holding a currency with a higher rate against one with a lower rate, and being on the correct side of that difference, earns a small credit each night. Holding it the other way costs a debit. On a standard lot of USDJPY, where the rate gap between the two currencies is meaningful, nightly swap can run several dollars in either direction depending on direction; on EURUSD, where the differential is currently narrower, the number is usually smaller but never zero. The exact figure is published by every broker per instrument and per direction, and it changes as central bank rates move, which is worth checking rather than assuming it is the same number it was six months ago.
Wednesday's triple charge
Most brokers charge triple rollover on Wednesday to account for the weekend, since a position held Wednesday night settles as though it were held Thursday, Friday and the weekend combined. A trade that would normally cost or earn $2 a night suddenly moves $6 that one night, a detail that surprises traders who assume every day's charge is identical. It is a small number on a single trade and a real one if a position habitually gets left open across a Wednesday close.
Why it matters even if you never hold overnight
A true intraday trader who is flat by the end of every New York session never sees a swap charge, and for most people trading a Daily Funded Session or a personal account with a strict same-day close, this is entirely avoidable cost. But it matters for two reasons anyway. First, platform clocks and personal clocks drift, and a position opened at 4:55 PM New York that is not manually closed can roll without the trader noticing until the statement shows it. Second, understanding swap explains price behavior around the rollover hour itself: liquidity thins, spreads widen, and brief unexplained wobbles around 5 PM are often nothing more than the market's daily settlement mechanics rather than a real signal worth trading.