What a Prediction-Market Trade Actually Costs

A prediction market’s displayed contract price is not necessarily the total amount a trader will pay. Under Kalshi’s fee schedule effective July 7, 2026, position cost and applicable trading fees are separate components. Start with the executed price for every contract filled, then add the trading fee and any applicable external charges. Spread, depth, and slippage should be reflected in the execution price rather than added again after actual fills are known. Kalshi’s July 2026 fee schedule documents this treatment and its worked fee examples.

The short answer: quoted price and all-in cost are different

Four measures are easy to conflate:

1. Quoted price: A displayed contract price that can be interpreted as the market’s implied expectation. A 60-cent YES contract is often read as roughly 60%, but that is neither a guaranteed true probability nor a promise that an order will execute at 60 cents.
2. Best executable bid or ask: The highest available bid for a seller or the lowest available ask for a buyer, limited to the quantity posted at that level.
3. Volume-weighted average fill price: The average execution price across every order-book level consumed. This is more useful than the top quote when the requested quantity exceeds available depth.
4. All-in effective price per contract: Total entry debit divided by the number of contracts filled.

For a conventional binary contract held to settlement, a separate measure is useful:

Fee-adjusted break-even probability = total entry debit ÷ maximum payout

All-in effective price per contract and fee-adjusted break-even probability are numerically equivalent only when each contract has a maximum payout of exactly $1.

For an entry purchase:

All-in entry cost = sum of executed contract prices + explicit trading fees + applicable external charges

When actual fills are used, the spread and price impact are already reflected in those execution prices. Adding them again would double-count the same friction. Before submitting an order, however, an estimate should use available order-book depth rather than multiplying the best ask by the entire requested quantity.

There is no universal prediction-market fee percentage. Venue, market, price, quantity, order type, product multiplier, rounding rules, and date can all matter. One community discussion about prediction-market fees and quoted prices illustrates the question, but it does not establish industry-wide fee practices. The defensible comparison is the exact contract’s executable price, current terms, and final order preview.

Quoted price, executable price, and spread

An order book turns a probability-like quote into executable bids and asks. Kalshi’s documented order book contains YES bids and NO bids; an ask on one side can be inferred from a bid on the opposite side.

In the documentation’s example:

• Best YES bid: $0.42
• Best NO bid: $0.56
• Implied YES ask: $1.00 − $0.56 = $0.44
• YES spread: $0.44 − $0.42 = $0.02

That two-cent difference is the bid-ask spread, not a two-cent transaction fee. It is the gap between what an immediate buyer would pay and what an immediate seller would receive at that moment. Kalshi’s order-book documentation explains the bid arrays, inferred asks, and available contract counts.

Side matters. A buyer seeking immediate execution generally looks at the ask; a seller generally looks at the bid. A chart’s midpoint, last trade, or probability label may sit between them and may not be executable now.

Quantity matters too. If only 20 contracts are offered at $0.44, a 100-contract purchase cannot be assumed to fill entirely at $0.44. The remaining 80 may execute at higher asks, making the volume-weighted average fill exceed the displayed best ask.

How Kalshi’s transaction fees change the quoted economics

Kalshi says it earns revenue by charging transaction fees based on a contract’s expected earnings. In the general fee schedule effective July 7, 2026, the dollar fee approximately follows a price-times-one-minus-price pattern, subject to product terms and rounding. The practical implication is that the general dollar fee is highest near a contract price of $0.50 and declines toward $0.01 or $0.99.

That shape arises because P(1-P) is greatest when P=0.50:

• At P=0.50: P(1-P)=0.25
• At P=0.10 or 0.90: P(1-P)=0.09
• At P=0.01 or 0.99: P(1-P)=0.0099

The payable amount can also vary with contract quantity, maker-versus-taker status, product multiplier, market-specific terms, and rounding. Consequently, “Kalshi charges X%” is generally too crude to produce a reliable all-in calculation.

A taker order immediately matches liquidity already resting in the order book. A maker order remains on the book rather than matching immediately. Resting orders are not universally fee-free: specified markets can carry maker fees. Kalshi says a maker fee applies only when an eligible resting order executes, while canceling an unfilled resting order does not incur that fee. Its fee help page also explains where fees appear in the trading interface.

The July 2026 schedule lists no settlement fee or membership fee. It does not eliminate every possible funding or intermediary cost: the schedule says card deposits can carry a fee, while banks and third-party payment processors may impose other charges.

Because schedules and product multipliers can change, use the fee schedule effective for the trade date, inspect the specific market’s terms, and confirm the amount in the final order interface. Kalshi says the displayed fee is available through the information icon beside “You’re buying.”

Worked table: quote, fee, total debit, and break-even probability

The table below applies the documented general-fee examples to 100 contracts. It assumes all 100 execute at the stated price and are held to a favorable $1 settlement, producing a maximum $100 payout. It excludes taxes, external charges, exit trades, and additional slippage.

Price	Position cost	Fee	Total debit / break-even
$0.10	$10.00	$0.63	$10.63 / 10.63%
$0.50	$50.00	$1.75	$51.75 / 51.75%
$0.90	$90.00	$0.63	$90.63 / 90.63%

The resulting winning net profits are $89.37 at a $0.10 entry, $48.25 at $0.50, and $9.37 at $0.90. These figures follow from the schedule’s listed position costs and fees.

The reusable formulas are:

Total entry debit = executed notional + entry fee

Winning net profit = settlement payout − total entry debit

Fee-adjusted break-even probability = total entry debit ÷ maximum payout

For 100 contracts purchased at $0.50:

• Executed notional: 100 × $0.50 = $50.00
• Entry fee: $1.75
• Total entry debit: $51.75
• Favorable settlement payout: $100.00
• Winning net profit: $100.00-$51.75=$48.25
• Break-even probability: $51.75/$100.00=51.75\%

This calculation treats the position as a conventional binary claim paying $1 per contract on a win and $0 on a loss. The break-even figure is an economic threshold, not a forecast that the event has a 51.75% chance of occurring.

Absolute fee and fee burden are different. The listed fee is largest at $0.50. At $0.90, however, the $0.63 fee consumes 6.3% of the position’s maximum $10 gross profit. At $0.10, the same $0.63 consumes 0.7% of the maximum $90 gross profit. A fee that looks small relative to notional can therefore be material relative to the remaining upside.

Why order size can matter more than the headline fee

A displayed ask applies only to the quantity offered at that level. A large immediate order can exhaust that quantity and continue into progressively more expensive offers. Its relevant contract price is the volume-weighted average execution price:

Average fill price = total executed notional ÷ contracts filled

Consider a single historical illustration, not a general venue ranking. In a July 28, 2026 snapshot involving 50,000 contracts tied to a Federal Reserve decision market, River Markets reported a $0.79 best ask on Polymarket US but an average immediate-execution price of $0.8262 for that size. Its analysis reported smaller top-ask-to-average-price gaps for the other venues in the comparison. River Markets published the underlying snapshot and execution assumptions.

The example was specific to one market, date, order size, and set of assumptions. It does not establish which venue is generally cheapest. River Markets sells routing services, creating a commercial interest in the comparison, and its preferred passive-execution scenario used an assumed fill rather than an observed or guaranteed execution.

The narrower lesson is that spread, depth, slippage, and venue fees can outweigh a small advantage in the top displayed ask. A venue that is cheaper for 10 contracts may be more expensive for 50,000, and the ranking can change as liquidity changes.

Before comparing prices across platforms, align:

• Exact outcome definition
• Resolution source and dispute rules
• Trading and resolution deadlines
• YES or NO side
• Requested quantity
• Order type
• Timestamp

Two contracts with similar titles can have different settlement wording or deadlines. Their price difference may therefore represent different underlying claims rather than an execution bargain.

Maker versus taker—and the cost of selling early

A marketable order prioritizes execution. It may cross the spread, incur a taker fee, and move through several price levels. Its immediate executable economics can be estimated from the live book and current fee terms, although prices and available quantities can change before the order is completed.

A resting limit order prioritizes price. It may secure a better fill or different fee treatment, but it can be delayed, partially filled, or never filled. Any maker-versus-taker comparison must use the current fee schedule and the multiplier for the specific market. “Maker” does not automatically mean “free.”

This creates an important distinction:

• Taker estimate: Based on liquidity presently available for immediate matching. It is grounded in the current book but is not guaranteed until execution.
• Maker scenario: Based on a proposed resting price and an uncertain fill. Until it executes, it is a modeled outcome rather than an observed trade.

Holding to settlement requires an execution decision at entry. Selling early can require another full round of friction:

Realized result = sale proceeds − original entry debit − exit fee − other external costs

Sale proceeds should be based on the actual bids filled, not a midpoint or last-traded price. An early sale may cross another bid-ask spread, encounter limited depth, experience slippage, and incur another transaction fee. A position entered partly as maker and partly as taker should be calculated fill by fill, using the applicable fee treatment for each portion.

A limit order can reduce cost if it fills on favorable terms. It can also create an opportunity cost if the market moves away and the order remains unfilled. That is an execution trade-off, not a universal recommendation for one order type.

A practical all-in cost comparison worksheet

Use one row per venue or execution strategy:

Field	What to record
Contract identity	Exact question, resolution terms, deadline, source, and dispute rules
Trade specification	YES or NO, quantity, timestamp, and intended order type
Execution	Best executable price, relevant depth, and expected average fill
Full economics	Fee, external charges, hold/exit plan, total debit, and effective price

Then calculate:

1. Expected executed notional Multiply each price level by the quantity expected to fill there, then add the results.

2. Total executable debit Add the explicit entry fee and any funding, payment-processing, blockchain, currency-conversion, or intermediary charges that actually apply.

3. All-in effective price per contract Divide total executable debit by contracts purchased.

4. Fee-adjusted break-even probability For conventional $1 binary contracts held to settlement, divide total entry debit by maximum payout.

5. Expected early-exit result, if relevant Model likely sale bids, available depth, the exit fee, and other charges separately. Do not assume the entry spread or liquidity will remain unchanged.

Compare matched contracts at the same quantity and timestamp. The decision rule is:

Compare total executable debit and fee-adjusted break-even probability—not quoted price or advertised fee alone.

A venue with no explicit transaction fee can still be more expensive because its spread is wider, its order book is thinner, its execution is worse, or external charges apply. Conversely, a venue with an explicit fee may have the lower all-in debit if it offers a sufficiently better fill.

Watch rounding on very small orders. Kalshi’s API supports sub-cent prices and fractional quantities, so intermediate calculations can extend beyond the displayed precision of an account balance. A precision-related balance adjustment can therefore make the final movement differ slightly from a simple price-times-quantity estimate; this is distinct from the ordinary trading fee. Kalshi’s fixed-point documentation describes these price, quantity, and rounding mechanics.

Before submitting an order, check the current fee schedule, live order book, market-specific terms, and final order preview. Start with the executable price for the intended quantity, add applicable fees and external charges, and account for another round of friction if the position may be sold early.

The quoted probability remains useful as a market expectation. The all-in effective price is the figure that determines cost, net profit, and break-even probability. This framework is educational and is not trading advice.