Prediction market fees: compare the whole transaction
Compare documented Kalshi and Polymarket fee models, price-sensitive examples, market exceptions and the costs a headline trading fee leaves out.
A quote is not the full transaction cost
This comparison records official fee documentation reviewed on October 12,2026. It concerns the specific Kalshi exchange schedule and Polymarket trading documentation linked below, not every app, intermediary or separately operated product sharing a brand. A market's contract price, its execution fee and the cost of funding an account answer different questions.
Two documented trading formulas
Kalshi's linked schedule is labelled effective July 7,2026. Its general taker formula uses contract count, contract price and a product multiplier; listed exceptions and maker-fee schedules can change the applicable calculation. An order left resting is not automatically subject to the same conditions as an immediately matched order.
Polymarket's documentation says taker fees apply to certain markets and gives a share-count × fee-rate × price × (1 − price) formula. It lists different category rates and identifies fee-free categories; makers are described as uncharged under that document. Use the exact market parameters rather than assuming every market has the crypto category's rate.
Reproduce one narrow example
For 100 contracts at a price of$0.50, Kalshi's general formula with multiplier 1 gives 100 ×0.07 ×0.50 ×0.50 =$1.75 before considering another applicable schedule. That matches the general table's100-contract example. It is not a quote for all series or all customer routes.
For 100 shares at$0.50 in Polymarket's documented sports-category example, rate 0.05 gives 100 ×0.05 ×0.50 ×0.50 =1.25USDC. This example concerns that category and documented unit. Different category parameters, prices or precision rules produce a different fee. The two examples do not establish a universally cheaper platform.
Buying, selling and settlement are separate
A planned early exit can incur another execution charge. For an illustrative position costing50 currency units and sold for 55, suppose entry and exit fees each total1.75. The net difference is55 −50 −1.75 −1.75 =1.50 before other costs. The5-unit price movement alone would overstate that net result. These are invented arithmetic inputs, not a real opportunity or a forecast.
Settlement is a different route from selling. Kalshi's reviewed schedule states no settlement or membership fee and no ACH deposit/withdrawal fee, while identifying separate conditions for cards and third-party routes. Polymarket states no platform deposit/withdrawal charge in the described USDC process but notes that intermediaries can charge. A trading-fee headline therefore does not settle the funding-cost question.
A practical comparison record
For a reproducible comparison, record the exact product, market or series, contract count, quoted price, immediate/resting execution, entry/exit plan, payment route and schedule date. Preserve the displayed fee and any relevant exception. Bid-ask spread or slippage is also distinct from a separately labelled fee. Our Polymarket policy-context article covers another dimension; a policy announcement is not a transaction-cost schedule.
Read the latest official document before relying on a later price. We have not traded either product or verified account availability. No general ranking, fee illustration or brand comparison establishes permission to participate from every jurisdiction.
Sources and checks
- Kalshi fee schedule, labelled effectiveJuly7,2026 · Checked 2026-10-12
- Polymarket official trading fee documentation · Checked 2026-10-12
- Polymarket trading overview and order models · Checked 2026-10-12