What Is an Iceberg Order?
Michael Whitman
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Trading since 2017, full-time since 2020
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YouTube creator, 137K subscribers
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Published 2026-09-15
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Updated
Iceberg order is a large order that displays only a small portion of its size in the public book, with the remainder hidden and released in further slices as each visible portion fills. The displayed quantity understates the real size, which is the reason the order type exists.
An iceberg order is a large order wearing a small one’s clothes. Understanding it is the fastest way to stop over-reading the depth displayed on a chart.
How it works
A large order is entered with a display quantity. Only that portion appears in the public book; the rest is held by the venue and is not shown.
When the visible slice fills, another appears. The level seems to replenish, which is what gives the order type its name - most of it is below the surface.
The hidden portion usually loses queue priority. Most venues place a refreshed slice behind orders that were displayed in full, which is the cost of concealment.
The problem it solves
Showing a very large order moves the market. A displayed order for a hundred thousand shares tells everybody what is coming, and price adjusts before the order is filled.
So the order is broken up. Showing a thousand at a time lets it sit in the book without announcing its full size, and the execution proceeds without the impact.
It is the same problem a dark pool addresses, solved differently. One hides the order on a separate venue; this one hides most of it on the public book.
A worked example
An institution wants to buy 200,000 shares. It enters an iceberg with a display quantity of 1,000 at a fixed limit price.
The book shows 1,000 bid at that level. Somebody sells into it, the level fills, and a moment later 1,000 appears again at the same price.
Repeat that two hundred times. The level absorbs every seller who arrives, and from outside it looks like a price that simply will not break.
It is not support in any analytical sense. It is one participant with a fixed limit and a lot of size, and when the 200,000 is done, the level offers nothing at all.
What you can and cannot infer
A level refilling repeatedly is a hint. Size appearing again and again at the same price is consistent with hidden quantity behind it.
It is not proof. Several separate participants replacing orders produce the same pattern, and the book does not label which is which.
And the hint expires without warning. The hidden quantity is finite, and nothing signals its exhaustion - the level simply stops refilling.
Which is why “the seller is done” is a conclusion only available afterward. Before that, a level holding and a level about to give way look identical from outside.
The trade-off the user accepts
Concealment costs queue position. On most venues a refreshed slice joins the back of the queue at that price, behind orders that were displayed in full.
So the order fills more slowly than a fully displayed one would. That is the price of not announcing the size, and it is paid on every refill.
The display quantity is the dial. A larger visible slice fills faster and reveals more; a smaller one conceals better and waits longer.
Which makes it a judgment about urgency. Somebody who needs to be done today shows more; somebody with a week shows less - and neither setting is correct in general.
The original data
A trader who probes a level for hidden size pays for every probe. Testing whether a level has more behind it means trading into it. Say each test is a small order whose round trip costs 0.1% of its value in spread and commission: five probes cost 0.5% of what was traded, whether the answer was useful or not.
And an inference about a level ages quickly. Whatever you conclude from watching it refill, the order behind it can be finished, canceled or repriced before the conclusion is old, and nothing on the screen announces which.
What this means for reading depth
Displayed size is a lower bound, not a measurement. There can always be more behind a price and never less, which makes the book asymmetric as evidence.
So a thin-looking level may be deep. Absence of displayed size is not absence of interest, and acting as though it were is the mirror image of the same error.
Retail platforms usually offer the order type too. The display quantity is a field on the order ticket at many brokers, so it is not exclusively an institutional tool.
And the useful conclusion is modest. Depth tells you what is shown; it cannot tell you what is available, and any level-two reading that forgets this is reading a number somebody chose to publish.
How this connects
It is the most common kind of hidden order, and the two terms are often used interchangeably, though some venues also allow fully non-displayed orders with no visible slice.
Execution algorithms use it constantly. Algorithmic trading that works a large position against VWAP will often rest as an iceberg at each price, so the refills track a schedule rather than any view.
Order flow readers look for it. Tape reading through time and sales, or a footprint chart and cumulative delta, can show more volume trading at a level than was ever displayed, which is the detectable fingerprint. A size filter set too high hides the refills, and how to read time and sales shows why the floor should move: a 5,000-share SPY print was 16.47% of an average lunchtime minute on 27 Oct 2026.
High frequency trading firms detect refills fastest, and a market maker will adjust its own quotes once it suspects persistent size at a price.
It is the legal opposite of spoofing. Spoofing displays size that is never meant to trade; an iceberg hides size that is.
Chart traders give it other names. A level that keeps absorbing sellers gets described as support and resistance, and Wyckoff readers call it accumulation, but the observable fact is simply refilling size.
How long it rests is a separate choice from how much it shows. An iceberg can be a day order or a good till canceled order, and it differs from a fill or kill order, which will not wait at all.
And when it finishes, price can move sharply, which is why stops placed just beyond an absorbing level often suffer slippage that gets misread as a stop hunt.
When it fails
The characteristic failure is trading against a wall that is not there. A large displayed order looks like a barrier, and positions get taken on the assumption that price cannot pass it.
Displayed orders can be canceled instantly. The wall disappears the moment it is approached, and the trade was built on a number that carried no commitment - the opposite error from missing hidden size, and produced by the same mistake of treating the book as a measurement.
A second failure is assuming a refilling level is one participant. Several separate orders look the same from outside.
A third is expecting the level to hold indefinitely. Hidden size is finite and gives no notice when it runs out.
A fourth is inferring intent from size. An index fund rebalancing and somebody with a strong view produce identical icebergs.
The question: The reading is clear. What does it leave out?
And a fifth is building a system on displayed depth. The input is a number participants choose, which means the system is measuring a decision about disclosure rather than a fact about supply.
Related
Order book covers the displayed depth this order type conceals. Limit order covers the order type an iceberg is a variant of. And liquidity covers the difference between displayed and available size.
This is the single best reason not to trust the depth on your screen. The book shows what people are willing to display, which is a different thing from what they are willing to trade. Every conclusion drawn from displayed size - a wall of sellers, a support level with real buying behind it - is drawn from a number that anybody can choose to understate.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.