Understanding Spreads, Slippage, and Execution Speed for EA Traders

Spreads, slippage, and execution speed are the three costs that quietly erode the edge of any automated strategy. A backtest that looks profitable with 0.5 pip average spread can turn unprofitable at 1.2 pips. A stop loss at 1.3050 that fills at 1.3045 is not a technical detail; it is real money. This guide defines each cost clearly, explains where they come from, and shows how to check that your broker is not silently taxing your EA - because these costs compound in ways that are invisible until you measure them explicitly.

The Three Costs Defined

• Spread is the difference between the bid and ask price of an instrument at a moment in time. If EURUSD is quoted 1.10502 / 1.10508, the spread is 0.6 pips.
• Slippage is the difference between the price at which you requested a trade and the price at which it was actually executed. Slippage can be positive (better) or negative (worse) but for stops is almost always negative.
• Execution speed is the time from your EA sending an order to the broker confirming it. Measured in milliseconds.

These three combined form the round-trip cost of trading. The MetaTrader 5 order execution documentation sets out exactly how execution modes handle price variation and requotes, which is worth reading before assuming your fill will match your intended price.

Why Spreads Move

Spread is not a fixed number. On most brokers it varies with:

• Session. London and New York overlap: tighter. Asia hours: often wider on European pairs.
• Liquidity events. Non-farm payrolls, central bank decisions: spreads can widen dramatically.
• Instrument. Major FX pairs: narrow. Exotics, indices, crypto CFDs: wider.
• Account type. ECN raw accounts: near zero but with commission. Standard accounts: wider spread, no commission.
• Weekend gaps. Spreads at Sunday open are usually much wider than mid-week averages.

Types of Slippage

Type	Cause	Typical impact
Market slippage	Fast price movement	Small on major pairs in calm markets
News slippage	Liquidity gap during releases	Can be many pips
Requote slippage	Broker offering a new price under Instant Execution	Variable
Weekend gap slippage	Price gap between Friday close and Sunday open	Can be very large
Latency slippage	Delay between EA decision and broker receipt	Grows with distance and load

Limit orders are executed at the specified price or better. Stop orders are executed at the specified price or worse. That single fact drives most of what a trader experiences with slippage on protective stops, and it is why EAs that rely heavily on stop-based exits are more exposed to slippage than those using limit exits.

Execution Modes Matter

MT4 and MT5 support several execution modes: Instant, Request, Market, and Exchange. Each handles price variation differently.

• Instant Execution allows a deviation setting; orders execute within tolerance or are requoted.
• Market Execution takes whatever price is available; no requotes.
• Request Execution demands confirmation of a quote before fill.
• Exchange Execution routes directly to a matching engine.

EAs written for Market Execution behave differently on Instant Execution accounts. Confirm the mode before deploying, and set the EA’s slippage parameter to match the mode your broker uses.

How to Measure Real Cost

Do not trust marketing. Measure.

1. Log spread every minute during the hours your EA trades.
2. Log requested vs filled price on every order.
3. Log the timestamp between OrderSend and the broker’s response.
4. Average across at least a month.
5. Compare the same measurements across two account types on the same broker.

A well-behaved retail account on a major pair might show average execution around 30-100 ms with a well-located VPS. On a colocated VPS, single-digit milliseconds are possible. Slippage on limit orders should be zero or positive; on stops it will usually be negative and should stay within a few pips on major pairs in normal conditions.

Practical Impact on Strategy Choice

• Scalpers are extremely sensitive to all three costs. Choose ECN, low latency, tight spreads.
• Grid and martingale EAs are less sensitive per trade but the cumulative cost adds up.
• Swing EAs are least sensitive and can tolerate wider spreads and slower execution.
• News EAs should assume worst-case slippage in position sizing.

Brokers we vet - IC Markets, Axi, Tickmill, AvaTrade, and Eightcap - publish execution reports or provide them on request. Our vetted broker comparison explains what to compare when narrowing down.

Reducing Execution Costs

• Use a VPS colocated near the broker’s trade server.
• Choose the account type matched to your EA (ECN for high frequency, standard for low frequency).
• Trade during high-liquidity hours where possible.
• Avoid trading through major news events unless your EA is specifically designed for it.
• Configure appropriate deviation settings in the EA.
• Use limit rather than stop entries where the strategy allows it.

The Combined Cost Perspective

A useful discipline is to calculate the total round-trip cost of an average trade: spread + commission + expected slippage + implicit latency cost. If that number is a meaningful fraction of the average pip target, the strategy has very little margin for error. Scalpers routinely operate on total round-trip costs of 0.3 to 0.7 pips against targets of 5 to 10 pips, meaning even small increases in any component matter.

FAQ

What is a good average spread on EURUSD?
On ECN raw accounts, often below 0.3 pips plus commission. On standard accounts, 0.8-1.5 pips is common.

Why is slippage worse on stops than on limits?
Stops become market orders when triggered; limits require the specified price or better.

Can execution speed alone make a strategy unprofitable?
Yes, for scalpers and news EAs. For swing EAs, less so.

Is zero slippage possible?
On limits, yes by design. On stops, no; slippage is a structural risk.

Should I trust broker execution reports?
Cross-reference with your own logs. Consistency between the two builds confidence.

How often should I re-measure execution costs?
Monthly if you rely on tight cost margins; at least quarterly for any live EA.

Trading foreign exchange and CFDs on margin carries a high level of risk and may not be suitable for all investors. This article is for educational purposes only and does not constitute financial advice.

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