Slippage is the gap between the price your EA asked for and the price it actually got. It is not a broker trick or a bug in the code — it is what happens when the market moves in the milliseconds between your order leaving the terminal and reaching the server. For an automated system firing hundreds of orders a month, a small slip on each one quietly adds up to a real dent in the edge.
What it is
When your EA sends a market order, it asks for the price it can see. By the time the order arrives, that price may be gone, and you fill at the next available one. Fill worse than asked and that is negative slippage; fill better and it is positive. Over many trades the two do not cancel out, because the worst slippage lands in exactly the moments your stops are firing.
Where it hits an EA
- Entries. Market and stop orders take whatever price is available, which in a fast move is not the one that triggered them.
- Stop-losses. A stop becomes a market order when hit, so in a sharp move against you it fills well past the level — the loss is bigger than the stop implied.
- Take-profits. These are usually limit orders, so they do not slip in your favour. They just fill at your price or not at all.
That last point is the trap. Your losses can slip wider, but your winners cannot slip better. The asymmetry is structural, and it always costs you.
Slippage lives in live fills, not in the tester. A backtest run at zero or fixed slippage will always flatter a fast EA. The gap between that result and your account is the slippage you are actually paying.
A worked example
A scalping EA trades 200 times a month at 1 lot (£10 per pip), with an average slip of 0.8 pips on entry and 0.8 on exit — 1.6 pips round trip.
200 × 1.6 pips × £10 = £3,200 a month, lost to slippage alone.
If the EA's gross edge is 3 pips a trade, that is 200 × 3 × £10 = £6,000 before costs. Slippage takes more than half of it, leaving £2,800 — and that is before spread and commission. The backtest, run clean, showed the full £6,000 and looked like a strong system. The live account tells the real story, and it is a much thinner one.
How to limit it
- Set a maximum deviation so the EA refuses a fill worse than a set number of pips instead of taking whatever is there.
- Avoid trading the news, where slippage is at its worst.
- Run a VPS close to the broker's server to cut the latency the slip grows in.
- Prefer limit entries where the strategy allows — they fill at your price or not at all.
- Do not run a scalper on a slow or wide-spread broker; the slippage will outweigh the edge.
The Karnek note
Karnek reads the fill price on every live trade, so you can measure the slippage you are actually paying and compare it with what the backtest assumed. It reads straight from your terminal, read-only, and can never place, modify or close a trade.
Written and reviewed by the Karnek Research team. Last updated August 2026.
Educational content only - not financial advice. Past performance does not predict future results. Trading carries significant risk.