Why is my child account's execution price different from the master account?

The short answer

You place a market order (or a stop-loss market order) in your master account. It fills at one average price. The same order is copied to your child accounts, and they fill at a slightly different average price. You compare the two and the numbers do not match.

This is normal and expected. Nothing was copied wrongly.

The quantity, the symbol, the buy or sell side and the product type are copied exactly. The execution price is the one thing that cannot be copied, because it is not decided by us or by you — it is decided by the market at the exact moment each order reaches the exchange, and the master and child orders reach it at two slightly different moments.

A limit price is different. A price you choose is copied to every child account exactly as you set it. So if what you want is the same price in every account, place a limit order in your master account instead of a market order.

Why a market order does not stay a market order

Under a rule from the market regulator for orders placed through a trading API, most brokers no longer accept plain market orders. Your child accounts are traded through your broker’s API, so this rule applies to them.

AutoTrader Web handles this for you with Market Price Protection (MPP). When a market order is copied to a child account, we convert it into a limit order at a price close to the live price, with a small safety buffer so it still fills quickly.

The important part is which live price is used:

For a copied market order, the protected limit price is worked out from the live price at the moment that child order is being sent — not from the price the master order filled at.

So the child order is priced against the market as it is now, not as it was when your master order filled. If the price has moved in between, the child’s fill price moves with it.

Where the price gap comes from

The gap is made of two things multiplied together:

How long it took for the child order to go out after your master order was placed.
How much the price moved during that time.

If the market is quiet, even a slow copy gives you almost the same price. If the market is moving fast, even a quick copy can give a visibly different price. And the gap works both ways — depending on which way the price moved, your child account can fill at a better price than the master, not only a worse one.

A simple example. Your master account buys a contract and fills at an average of ₹100.00. About a quarter of a second later the child order is prepared. The live price is now ₹100.10, so the protected limit is set a little above that, and the child order fills at about ₹100.10. Your master shows ₹100.00 and your child shows ₹100.10. Both are correct. Ten paise of price movement happened in between.

This is not caused by the conversion. Even if market orders were still allowed and we sent a plain market order for the child, it would still fill at the price available at that later moment. The conversion protects you from a very bad fill; it is the time gap that creates the price difference.

Stop-loss market orders work a little differently

A stop-loss market order is worth understanding on its own, because it behaves better than people expect.

The order is copied when you place it, not when it triggers. So the child order is created at a calm moment, well before the market reaches your trigger.
Both the master order and the child order then rest at the exchange with the same trigger price, and each one triggers on its own, at its own broker, at the same time. There is no copying delay in the middle of a fast move.
For the child account, the protected limit price is worked out from your trigger price, not from the live price.

So for a resting stop-loss order the timing gap mostly disappears. What can still differ is the fill itself: the master’s stop-loss market order takes whatever price the market gives at that instant, while the child’s converted order fills only within its protected limit. In a sudden jump the child can fill at a different price, or in a very sharp move it may not fill at all. A wider Market Price Protection setting (Normal or Aggressive) gives the child order more room to fill.

If you want the same price in every account, place a limit order

This is the simplest and most reliable answer, and it is worth knowing before you try anything else.

Place a LIMIT order in your master account instead of a market order.

A limit price is a number you choose, so it does not have to be worked out again for each account. Your master order’s limit price is copied to every child account exactly as you set it. Nothing is recalculated, and no live price is looked up. The same is true for a stop-loss limit order — both your trigger price and your limit price are copied across unchanged.

What this gives you: every account has the identical price, so no account can ever fill worse than the price you chose. That is the price certainty users are really asking for when they compare a master fill with a child fill.

What it does not promise: the fill can still differ a little. An order can fill at a better price than its limit, and a large order fills across several price levels, so average prices can still vary slightly between accounts.

The trade-off — and it is a real one. A limit order only fills at your price or better. If the market moves away before it is filled, it may fill partly, or not at all, in any account. A market order buys certainty of getting filled; a limit order buys certainty of price. You cannot have both, and that is a trading choice only you can make.

How to make the gap smaller if you keep using market orders

If you need the certainty of getting filled, stay with market orders and work on the delay instead. You cannot control how the price moves. You can control how long the child order takes to go out.

1. Put your master account with a high-performance broker. This is the biggest lever here. Master-child copying can only start after your broker tells us there is a new order in the master account. With a high-performance broker that notification reaches us in about 0.2 seconds or less, so the child orders go out almost immediately and meet almost the same price. With a slower broker the same step can take 2 to 3 seconds, and in a fast market that is enough for a visible price difference.

See the list of high-performance brokers on the copy trading page. Two things to note there:

This matters for the master account only. A child account gets no benefit from it.
A few brokers sell a free and a paid API tier, and only the paid tier sends the instant notification. The fee is charged by the broker, not by us.

2. Or use PMS copy trading instead. With PMS copy there is no master account and no waiting for a broker notification — you place the order once in our system and it goes to all your accounts together. That removes the notification wait completely, so the prices across your accounts stay closest. PMS copy is the recommended method for traders who place orders by hand rather than through an algo.

3. Check your Market Price Protection setting. If your child orders are not filling in fast markets, a wider buffer (Normal or Aggressive) helps them fill. Remember that a wider buffer only gives the order more room — it does not make it fill at a worse price on its own. Your order always fills at your limit price or better.

How to check your own numbers

Do not guess at the delay — measure it. Everything you need is on your own orders.

Copy Log → Timing Statistics. Open Trading → Portfolio → Orders tab → Copy Log for the master order. It shows how long each stage took, per child account, and splits the time between our system and your broker system. If the broker time is large, the delay was at your broker.
Activity logs. Open Tools → Activity. For a converted order this records the limit price we used and the live price it was worked out from, so you can see exactly what the market looked like when your child order went out.
Compare the right timestamps. Order screens usually show the last modified time, not the created time. Comparing the wrong one makes a fast copy look slow. See Investigation of delay.

What to check before reporting it as a problem

Report it to us if any of the following is true — these are real problems, unlike a small price difference:

The child order quantity is wrong for the multiplier you set.
A master order was not copied at all to a child account.
The Copy Log shows our system taking a long time (the broker column being large points at your broker, not at us).
The gap is large and repeats even when the market is quiet.

A small difference in average execution price, on its own, is expected behaviour in every master-child copy system.

When this happens