Copy-Trading Slippage: Why Your Results Differ From the Master's

You copied every trade, yet your month reads +6% while the master posted +9%. Before assuming foul play, understand the four mechanical gaps between a master account and its copiers — each measurable, each with a different fix.

1. Fill lag

The copier sees the master's fill, then sends your order: that round trip is the lag. Measured across real linked accounts on the same broker, healthy lag medians run 130–230 milliseconds — fast enough that price rarely moves meaningfully. Lag hurts when it stretches to seconds (overloaded copier VPS, cross-broker copying, symbol mapping lookups) or when the strategy scalps news candles where 500ms is the trade.

2. Entry/exit slippage

Even with instant copying, your fill price differs from the master's because the book moved. Slippage is signed: negative means you got a better price. What matters is the median across many trades — a fair setup oscillates around zero; a consistently positive median means you systematically pay more on entries or receive less on exits. Broker execution quality drives much of this; our scoreboard measures it per broker from real fills.

3. Size ratio and rounding

A follower at 0.4× the master's size can't copy a 0.01-lot master trade at 0.004 lots — brokers round to 0.01 minimum. Rounding distorts small trades far more than large ones, so a master who scales in with many small entries copies worse than one who trades in fewer, larger clips. This is also why comparing raw dollar P&L between master and follower is meaningless: compare profit per lot instead — same-basis numbers that expose real divergence and forgive size differences.

4. Fees

Performance fees leave the follower'saccount. The master's track record doesn't show them, yours lives them. On typical 20-30% profit-share arrangements this alone explains a 2-3 percentage-point monthly gap on a +10% month. How to read every copy-fee format your broker posts.

Measuring all four at once

TradeStats' copy-quality report links a follower account to its master and computes each gap from broker data: copy rate(trades matched since your first copy — a mid-month subscriber isn't punished for earlier trades), fill lag median and p90 (clock-skew corrected across brokers), entry/exit slippage in points, copy size ratio, and a monthly table with $/lot for both sides plus your net after fees. If something diverges, the report shows which of the four gaps it is — no guessing, no accusations, just verifiable numbers.