Find Out Whether Your Whole Order Can Fill

Market depth is the quantity of contracts available to buy or sell at different prices in an order book. It tells you whether your whole order can fill near the quoted price. In the fictional example below, buying 100 Yes contracts consumes three price levels: a 60¢ best ask becomes a 63.1¢ average purchase price before fees. The displayed quote is the price of the first available contracts, not a promise for your entire order.

Choose your order size; expand the price limit and fee settings to compare fills in the fictional book.

Read The Side Of The Book You Will Trade Against

An order book lists resting orders and their quantities at each price. A bid is a price someone is willing to pay; an ask is a price someone is willing to accept. To buy a Yes position immediately, inspect the Yes asks, starting with the lowest price. To sell it immediately, inspect the Yes bids, starting with the highest price.

Your own willingness to buy does not make the bid side the source of an immediate purchase. You need a seller, so you trade against an ask. Similarly, an immediate sale needs a buyer, so it trades against a bid. Confusing these sides can make an order look cheaper or easier to exit than it is.

Kalshi’s order book can display orders in bid or ask terms, so check which view you are reading before interpreting the numbers. Kalshi explains its order-book display here. A price shown in a different outcome or display convention should not be silently treated as a Yes ask.

The spread is the best ask minus the best bid. Depth is the quantity available across the prices you would accept. The spread describes the gap between the best prices; depth describes how much you can trade at those prices and beyond them.

Historical Volume Does Not Reserve Your Next Fill

Depth differs from volume: volume describes trading that has already happened; depth describes orders available now. Kalshi’s trading glossary distinguishes these measures. A busy market’s historical volume does not guarantee enough liquidity for your next order. See what volume means on Kalshi.

For execution, the relevant quantity is not all trading in the market, nor even all orders visible in the book. It is the quantity on the side you need, at prices you will accept. Orders above your buying ceiling do not help fill your purchase within that ceiling. Orders below your selling floor do not provide an acceptable exit.

Depth is therefore specific to an order size and a price range. The same book can accommodate a small purchase entirely at the best ask while forcing a larger purchase through several more expensive levels. Calling a market “liquid” without stating the intended trade size hides that distinction.

Define The Contract Before Pricing The Position

Suppose a fictional market resolves Yes only if a named agency’s initial October report shows an index strictly above 100, with publication due by October 31. A reading of exactly 100 does not qualify; later revisions do not count under these assumed rules.

Those details define what you are buying. A belief that the index will eventually exceed the threshold is not necessarily a belief that this particular contract will resolve Yes. The initial report, threshold wording and publication deadline all belong in your assessment before you compare that assessment with an execution price.

Actual resolution rules determine which source, deadline and edge cases apply—not just the market title. Polymarket’s resolution documentation describes these rule components and the $1 winning-token payout. That documentation is not a substitute for reading the rules of the specific market you intend to trade.

For the calculation here, assume each Yes contract pays $1 if the fictional market resolves Yes and $0 if it resolves No. The order book and fee below are illustrative, not live market data or a platform fee quote.

Read Level Quantity Separately From Cumulative Quantity

The fictional Yes asks are:

Yes Ask	Contracts At Level	Cumulative Contracts
60¢	20	20
62¢	30	50
65¢	50	100

The fictional Yes bids are:

Yes Bid	Contracts At Level	Cumulative Contracts
58¢	40	40
56¢	60	100

“At level” is the quantity offered at that single price. “Cumulative” adds that level to the better-priced levels before it. At the 62¢ ask, there are 30 contracts at that price and 50 available at 62¢ or less. Those are not two separate pools of contracts.

For a buy, work down the asks from cheapest to most expensive. For a sale, work down the bids from highest to lowest. Stop when you have accounted for your intended quantity or reached your price limit.

The best spread is 60¢ − 58¢ = 2¢. That calculation uses only the top prices. It says nothing by itself about the average cost of buying or selling 100 contracts.

A 100-Contract Purchase Averages 63.1¢, Not 60¢

Assuming these orders remain available and your order can execute through 65¢, buying 100 contracts costs: (20 × $0.60) + (30 × $0.62) + (50 × $0.65) = $63.10.

Your average fill price is $63.10 ÷ 100 = 63.1¢, which is 3.1¢ above the best ask. This difference comes from consuming several price levels. It does not require the displayed book to change during the trade.

Only the first 20 contracts are available at 60¢. The next 30 cost 62¢ each, and the final 50 cost 65¢ each. Multiplying the full order by the best ask would ignore the limited quantity available there and understate the purchase cost.

The average is quantity-weighted, not a simple average of the listed prices. A level supplying more contracts contributes more to the total. Calculate total dollars spent across the filled levels, then divide by the number of contracts actually filled.

The worst fill price and the average fill price also answer different questions. Here, 65¢ is the highest contract price paid, while 63.1¢ is the average across all 100. You need the former to check a price ceiling and the latter to evaluate the position’s total cost.

A 62¢ Limit Protects Price But Leaves A Partial Fill

With the displayed asks unchanged, a 62¢ buy limit for 100 contracts can fill only 50 immediately: the 20 offered at 60¢ and the 30 offered at 62¢. The 50 offered at 65¢ are outside that limit.

The immediately executable portion costs (20 × $0.60) + (30 × $0.62) = $30.60, averaging 61.2¢ across the 50 filled contracts. That is a calculation from this fictional book, not a prediction that the remaining order will fill later.

The remainder may rest, depending on order settings. Kalshi’s limit-order guide explains partial fills and why execution is not guaranteed. The limit controls the contract price, not the total including fees.

A limit is also not a request to pay that price for every contract. In this example, a buy allowed through 65¢ still takes the cheaper displayed asks first. The ceiling permits the final level; it does not turn all the earlier fills into 65¢ purchases.

If your decision depends on acquiring the full position, a partial fill changes the position you actually own. Evaluate the filled quantity rather than continuing to use the intended quantity in payout or exposure calculations.

Fees Raise The Expected-Value Break-Even Probability

Now assume an illustrative total entry fee of $1.70—not a platform fee quote. For the fully filled 100-contract purchase, the all-in cost becomes $64.80.

If held to ordinary binary settlement, with no further charges, the expected payout is the probability of Yes multiplied by $100. The expected-value break-even probability is therefore $64.80 ÷ $100 maximum payout = 64.8%.

That is a cost threshold, not evidence that the event has a 64.8% chance. It tells you the probability at which expected payout equals the assumed cost. Your probability assessment must come from the event and its resolution rules, not from the calculator’s output.

Actual fees depend on the venue and contract. Kalshi’s event-contract fee schedule, effective July 7, 2026, distinguishes immediately matched trades from resting orders and lists exceptions. The illustrative $1.70 should not be applied to other orders as though it were a universal rate.

The tool lets you change the total entry fee, but it does not estimate a venue’s fee schedule. If you change the order size or price limit, enter the fee appropriate to the modeled fill. Keeping $1.70 unchanged is an explicit assumption, not an automatic recalculation of fees.

The Exit Side Makes This A Costly Round Trip

If the displayed bids remain available after your purchase, selling those 100 contracts immediately would return: (40 × $0.58) + (60 × $0.56) = $56.80.

The purchase-to-sale loss is $63.10 − $56.80 = $6.30 before fees. A narrow-looking best spread did not mean a cheap round trip at this size. The purchase consumed several ask levels, and the sale would consume several bid levels.

This is a hypothetical immediate exit using an unchanged snapshot. It is not a forecast of what you could sell for tomorrow or after new information arrives. Future bids may differ, and the displayed orders may no longer be available even by the time you submit your sale.

The distinction matters if you plan to trade out rather than hold to settlement. A $1 winning payout is the settlement assumption for this example; it is not a standing offer to buy your position before resolution. An early exit depends on the buying interest available then.

Inspecting only the asks answers whether you can enter. Inspecting the bids answers what the displayed book could currently pay for your exit. Neither side guarantees the other will remain deep.

Treat The Calculator As A Snapshot, Not A Reservation

The embed models orders of 1–100 whole contracts against the displayed levels. It assumes those levels remain available, fills eligible asks from cheapest upward, and compares the filled position with the displayed bids. It does not model changes to the book while an order executes.

If your limit is below 60¢, none of the shown asks qualifies. There is no average fill price or break-even probability to report because there is no modeled purchase. If your limit excludes some levels, the result reports the partial fill rather than inventing liquidity for the remainder.

There is no evidence here about quantities beyond the displayed 100 contracts on either side. The tool therefore does not estimate a larger order. Likewise, its exit comparison excludes exit fees, while its settlement break-even calculation assumes no further charges.

Before submitting a real order, recheck the live quantities and fee preview. Resting orders can be filled or cancelled; a depth snapshot is not a reservation. Compare the resulting cost with your assessment of the exact contract, not merely with its headline quote.

Depth helps estimate execution costs. It does not establish the event’s probability or make unclear resolution wording safe. Use it within the broader pre-trade reading checklist, and size the position within what you can afford to lose.