Order Types and Slippage
The order type you choose decides whether you control your price or your fill. You rarely get both.
Every order type is a trade-off between certainty of price and certainty of execution. You almost never get both, and knowing which one you are giving up is the difference between a planned trade and a surprise.
Slippage is not a broker defect. It is a structural feature of how markets match buyers and sellers, and it becomes predictable once you understand when it appears.
Market orders: guaranteed fill, not price
A market order says: get me in now, at whatever price is available. You are guaranteed to be filled in any liquid market, but you are not guaranteed the price you saw on screen.
Between the moment you click and the moment your order reaches the matching engine, the price can move. In normal conditions the difference is a fraction of a pip. In fast conditions it is not.
Limit orders: guaranteed price, not fill
A limit order says: fill me at this price or better, and if you cannot, do not fill me at all. You control the price completely, and you give up any guarantee of being filled.
This is the right choice when the exact entry price matters to your risk-to-reward calculation. It is the wrong choice when you need to exit immediately, because the market may simply pass through your level without filling you.
Stop orders become market orders
This is the single most misunderstood order type. A stop-loss order does not guarantee you exit at the stop price. Once triggered, it becomes a market order and fills at the next available price.
In a fast, gap-prone market, that can be meaningfully worse than your stop level. Guaranteed stop-loss orders exist precisely to cap this, and brokers charge a premium for them.
When slippage appears
Slippage clusters around predictable events. Major economic releases produce the worst of it, because liquidity briefly evaporates while everyone tries to trade at once. Market open does the same, as does any thin session for that instrument.
If your strategy depends on tight entries around news, you are not trading the news — you are trading your broker's ability to fill you during it. Measure realised slippage by session before you commit to a scalping approach.
Volatility Heatmap by Asset Class
UTC • Current Hour: 16:00
Key takeaways
- A market order guarantees the fill, never the price
- A limit order guarantees the price or better, never the fill
- A stop order converts to a market order once triggered — it is not a price guarantee
- Slippage spikes on news, at open, and in thin sessions; measure it before relying on tight entries
- Market orders guarantee the fill, not the price
- Limit orders guarantee the price or better, not the fill
- Stop orders become market orders once they are triggered
- Slippage widens during news, thin liquidity, and market open
Using a market order into a major news release and then blaming the broker for the fill price.
Reading is not verification
Take the concept you just read and turn it into explicit rules, then test it. That is the only way to know whether it actually works.
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