Slippage is normal and not inherently unfair. A market order takes the best available price, and in fast conditions that price has already changed. It can go in your favour too, though traders remember it only when it does not.
It matters most for stop losses. A stop is an instruction to sell at market once a level trades, so in a gap or a violent wick it can fill far below where you set it. Guaranteed stops exist at some brokers for a fee.
The mistake it causes: assuming a backtested stop loss equals a real one, and scalping instruments where slippage is larger than the edge.
Where it comes from
A market order takes the best available price. If your order is larger than what is resting at that price, it consumes the next level, and the next, until filled. Your average fill is therefore worse than the quote you saw. That is slippage, and it is mechanical rather than unfair.
| Condition | Typical slippage |
|---|
| Major pair, active session | Negligible |
| Thin pair or off-session | Noticeable |
| News release | Severe |
| Weekend gap | Can be enormous |
It matters most where you least want it
A stop loss is an instruction to sell at market once a level trades. It guarantees the trigger, never the fill. In a gap or a violent move the fill can be far past your level, which means your actual loss exceeds the planned 1R. Any journal showing repeated losses worse than −1R is showing slippage, a widened stop, or both.
It is not always against you
Positive slippage happens too, and traders simply do not notice it. What makes it feel one-sided is that the conditions producing large slippage, panic and news, are also the conditions where you are most likely to be the one needing out.
Reducing it
- Use limit orders for entries. You give up certainty of fill and gain certainty of price.
- Trade liquid instruments during their own session.
- Avoid holding tight stops through scheduled news.
- Consider guaranteed stops, where offered, for event risk. It is one of the few fees worth paying.
Backtests do not include it
This is why strategies that look excellent in testing underperform live. A backtest assumes you got the price on the chart. Add realistic slippage and the spread, and many short-term systems stop working entirely.
