The spread
The spread is the gap between the buy price (ask) and the sell price (bid). You pay it when you open a trade: a buy starts slightly below break-even and must first recover the spread. Spreads widen around news and when markets are thin.
Commission
Some accounts charge a commission per lot or per trade instead of, or on top of, a spread. Compare the total cost, not just one part.
Slippage
Slippage is the difference between the price you expected and the price you got. It happens when prices move quickly, for example at economic releases, and is more common with market and stop orders.
Swap or overnight financing
Leveraged positions held past the daily rollover usually pay or receive a financing charge, called a swap. Over days and weeks it can add up, especially with large positions.
What it means in practice
Costs make short-term trading harder. A trade that gains less than the spread is still a loss. When you work out profit and loss, subtract all of these items from the gross result.
Related:Profit calculatorMarket hoursLeverage and margin
Educational content, not investment advice.