It works both ways. If you are in negative and you hold over night ( depends on what time your broker closes the day candle ) and you are charged a swap than it will be reverse, where a swap is paid to you if you are in the black on the same trade.
Brokers who charge swap generally tend to charge a lower spread. Usually Shariah compliant or Islamic brokers dont charge swap.
You are only charged or paid a swap if you hold over night.
In the bigger scheme of things, a swap doesnt really affect your bottom line.
you’ll experience a swap/rollover anytime you hold a position across the 5pm-NY-time point. (apparently, not every broker uses that same time, but i think the vast majority do).
if you’re holding a position past 5pm-NY-time then we’re presuming that you’re more of a swing trader, not a day trader, and thus (a) your position is smaller than a day trade because (b) your expectations for P&L in terms of ‘pips’ are larger than a day trader. thus, the rather small swap/rollover should be next to invisible in your trades, and i think it’s about the same size as the bid/ask spread.
however, if you’re holding a position overnight even though you don’t normally do that, then it may indicate that you’re breaking your trading rules and possibly ‘hoping’ that the market brings your trade back to a better spot. you probably also have a large(er) position since typically you close all trades before 5pm.
so - how do you trade? does your plan tell you to be flat by 5pm NY time, or does your plan involve holding trades for 2-5 days (in which case the swap is going to be part of the picture, albeit a tiny part)