Spread, slippage and swap: the hidden costs of EA trading

Spread

The spread is the difference between the buy price and the sell price. You pay it on every trade the moment it opens. It widens at news releases, at the daily rollover and in thin markets.

Commission

Some accounts use a tight spread plus a fixed commission per lot. Add the commission to the spread to see the true round-trip cost. Compare accounts on the all-in figure, not the spread alone.

Slippage

Slippage is the difference between the price you requested and the price you received. It is most common during fast moves and low liquidity, and it can be positive or negative. Short-term EAs are the most sensitive to it.

Swap

Swap, or rollover, is the interest charged or paid when a position is held past the daily cut-off. It differs by symbol and direction, and it is tripled on one day of the week. EAs that hold positions for days should include swap in their tests.

How to check your own costs

Measure them on a demo or small live account.

• Watch the typical and the maximum spread on your symbol across a full day.
• Read the swap values in the symbol's Specification window.
• Compare a few trades' requested and executed prices in the Journal.