Why your copied P&L never exactly matches the trader's

Copying is proportional, not identical

The core mechanic of copy trading is a ratio. If a trader runs a $450,000 account and you run $4,500, you are at 1% of their size, and a sensible platform scales every position accordingly — they open 10 lots, you get 0.1.

That ratio is what makes percentage returns transferable. If the trader is up 4% on the month, a proportionally-sized copier should also be up roughly 4%, on a much smaller base. The dollar figures differ enormously; the percentage is the thing that travels.

Everything in the rest of this guide is a reason the word 'roughly' is doing real work in that sentence.

Minimum lot size: the gap that hits small accounts

Brokers enforce a minimum tradable size, typically 0.01 lots. If your proportional share of a position computes to 0.004 lots, it cannot be placed as-is.

There are two ways a platform can handle this, and the difference is not cosmetic. It can skip the trade, in which case you miss that position entirely. Or it can round up to the minimum — which quietly places you at several times your intended exposure on exactly the trades where your share was smallest.

Rounding up sounds generous and is dangerous: it breaks the proportionality that made the trader's percentage return meaningful for you, and it does so asymmetrically, concentrating oversized positions in the smallest accounts. If you are copying with a small balance, this is the single most important behaviour to ask about.

• Skipped: you miss some positions, and your return tracks slightly under the trader's.
• Rounded up: you take positions several times larger than proportional, and your drawdown can far exceed theirs.

Spread, commission and swap

You and the trader are not necessarily at the same broker, and even at the same broker you may not be on the same account type. Spread is charged per position, so a wider spread on your side is a fixed drag on every single copied trade.

The effect scales with trade frequency, not with position size. A scalping strategy taking 40 positions a week will feel a half-pip spread difference far more than a swing strategy holding four positions a month — which is why a strategy that works at the trader's execution costs can be flat or negative at yours.

Overnight swap works the same way. If a strategy holds positions for days, the swap rates on your account are part of your result and none of the trader's published figures.

Slippage and the delay between their fill and yours

A copied order is placed after the original: the platform has to receive the trade event and send an order to your broker. On liquid instruments in normal conditions this difference is small and cuts both ways.

It stops being small in exactly the conditions that matter most — news releases, session opens, and any fast move. This is also when the entry price difference is largest, and it applies to exits as well as entries.

There is no setting that removes this. It is a structural property of copying someone rather than being them, and it is a reason to be sceptical of any strategy whose published edge is only a few pips per trade.

What a healthy gap looks like

Some divergence is normal and expected. A copied account should track the trader's percentage return closely, with a consistent small drag from spread and slippage.

What is not normal is divergence in the wrong direction or divergence that grows. If your drawdown is materially deeper than the trader's, your position sizing is not proportional — the most common cause being lot-size rounding on a small account.

The check is straightforward: take one closed position, compare your lot size to theirs, and compare that ratio to the ratio of your account balances. If those two numbers don't broadly agree, sizing is the problem, not the strategy.

Common questions

Should my copy trading return match the trader's percentage exactly?

No. Expect to track slightly under, because spread, commission and slippage are charged on your side of every position. A consistent small drag is normal; a growing or opposite-direction gap usually indicates a sizing problem.

Why did I miss a trade my trader took?

Most often the proportional size fell below your broker's minimum lot, so it could not be placed. On a small account this happens on the trader's smaller positions.

Does a bigger account copy more accurately?

Generally yes, because proportional sizes land further above the lot minimum and rounding matters less. Spread and slippage still apply at any size.