The number on the tile is not a price you can trade
The figure shown on a market is the midpoint of the book, and when the book is wide it is not even that. What you actually pay is set by the depth underneath it.
A market tile says 63. You form a view, you decide 63 is cheap, you submit an order. You do not necessarily trade at 63, and on a thin market you may not trade anywhere near it.
This is not a display bug. It is what the number means, and the documentation says so plainly enough — it is just that almost nobody reads the page where it says it.
Your Call evaluations trade Polymarket, so the specifics below are that venue’s. The general shape holds anywhere contracts trade against a book.
There is a book, not a formula
Prices are not set by the venue and not computed by a curve. Polymarket runs a central limit order book: per its documentation, prices “emerge from supply and demand as users trade with each other.” Buy orders rest at the highest prices people will pay, sell orders at the lowest prices people will accept, and the gap between the best of each is the spread.
That means there is no single price. There is a price at which you can buy and a different, lower price at which you can sell, and the distance between them is a real cost you pay on entry and again on exit.
What the tile is actually showing you
The displayed figure is the midpoint of the bid-ask spread. Not the best offer, not the last trade — the number halfway between the two sides.
On a tight market that is a reasonable summary. On a wide one it is a price that nobody is quoting. If the best bid is 55 and the best offer is 71, the tile reads 63, and 63 is a number you cannot transact at in either direction.
There is a second layer to this, and it is the part worth remembering. Per the same documentation, if the spread is wider than $0.10, the display stops showing the midpoint and shows the last traded price instead.
Read that carefully, because the substitution happens in the wrong direction for you. Precisely when the book is widest — when the midpoint would be least informative — the display swaps to a historical print. A last trade is a fact about a moment that has passed. It can be minutes or hours old. It tells you what someone once paid, not what anyone is currently willing to accept.
So the displayed number degrades exactly in the conditions where you most need it to be accurate, and it does so without announcing that it has changed meaning.
Depth is the part you have to go and look at
Behind the best bid and offer sits a queue of resting orders at progressively worse prices. A small order takes the top of the book. A larger one walks down it, filling part at the touch and the rest at whatever is underneath.
The order types available shape how much of that you absorb. The documentation lists limit orders as Good Till Cancelled, Good Till Date, and Post-Only — the last of which only ever adds liquidity and is rejected if it would match immediately. For immediate execution there are two market variants: Fill and Kill, which takes whatever liquidity is there and cancels the remainder, and Fill or Kill, which either fills the whole order at once or does nothing.
Tick size is set per market rather than globally, and the documented values span a wide range — 0.1, 0.01, 0.005, 0.0025, 0.001, 0.0001. A market quoted in ten-cent increments has a structurally wide minimum spread before any question of liquidity arises. Minimum order size is also per-market. Both are worth checking on an unfamiliar market rather than assumed from a familiar one.
Why execution costs more inside an evaluation
Three reasons, all of them structural rather than a matter of degree.
The upside is capped and the slippage is not. No matter how well an event goes, at most 0.5% of account size counts toward the Equity Growth Target. A fill two cents worse than you intended does not reduce a proportional reward — it comes out of a fixed ceiling. The worse your execution, the smaller the share of an already-capped outcome you keep.
A worse fill costs you twice. The commission is charged on cost basis — what you actually pay for the shares, not what they would be worth at settlement. Paying up therefore raises the fee as well as the entry, and the fee comes out of equity the moment you open.
Your account’s own measurement inherits the book’s noise. Every rule is measured against live equity, and live equity marks your open positions continuously. On a wide book that mark moves when a quote moves, not when a trade happens. A single participant pulling a resting order can shift what your account believes your position is worth, and every drawdown limit is measured against that number. Thin markets do not just cost you on entry; they make your own risk metrics jumpier.
The exit is the half people skip
Opening orders are restricted to the 0.20–0.80 band. Closing orders are not, so you can always get out in principle. In practice, getting out of a thin market means you are the one crossing the spread, into a book that may have thinned further since you entered — and the per-event cap means there is no version of that trade where you are compensated for the cost of leaving.
The habit that follows is unglamorous: before sizing a position, look at the depth rather than the tile. Ask what it would cost to get out of the size you are about to put on, today, at the prices actually resting. If the answer is uncomfortable, that is not a reason to trade smaller with the same conviction — it is information about whether the market is tradeable for you at all.
I am not going to give you a depth threshold. It varies by market and by hour, and any general figure I offered would be invented rather than measured. What I will say is that a spread wide enough to trigger the last-traded fallback is a market telling you something about itself, and the right response is usually to work a limit order and let it sit rather than to cross and find out.
Evaluations are conducted on simulated accounts. Not financial advice.