Polymarket vs Kalshi: contracts, costs and access

2 binary contracts are not the same contract

Both venues list binary event contracts: the winning side ordinarily settles at 1 dollar, the losing side at 0. Polymarket's documentation describes prediction market contracts as having specified outcomes and resolution criteria, and treats the traded price as an implied probability once you account for mechanics and costs. Kalshi's help pages describe prediction event contracts that pay ordinarily 1 or 0 and trade through buyers and sellers. So the payout unit is not where the venues differ. The difference sits in the contract document you are actually buying: which source settles the question, by which deadline, and how edge cases are handled. 2 markets can carry the same headline and still be different instruments.

Polymarket's taker fee is a formula, not a flat percentage

Polymarket charges takers, not makers, and only on fee-enabled markets. The documented formula is fee = C x feeRate x p x (1-p), where C is the number of shares and p is the price. The category feeRate runs from 0 to .07: crypto .07, sports .05, economics .05, culture .05, weather .05, general/other .05, finance .04, politics .04, mentions .04, tech .04, geopolitics 0. Because the formula contains p x (1-p), the fee peaks near a price of .50 and shrinks toward both ends. Polymarket's own worked numbers: 100 crypto shares at .40 costs 1.68, which is 4.2 percent of the 40 dollars of notional, not 7 percent of your cash. 100 sports shares at .50 costs 1.25. Check the market's fee parameters and the current docs before you send an order, because rates and categories change. A wallet or bridge provider can also charge you separately.

This formula is why a visible price gap is not a verdict. If one venue shows .43 and another shows .45, you still cannot say which is cheaper for your order until you apply the category rate to your share count: 100 shares at .40 and 100 shares at .50 carry different fees on the same venue. The example above is arithmetic from the published formula, not a forecast about any market.

Kalshi's fee schedule has to be read live

No numeric Kalshi fee schedule is available in the documentation used here, so this comparison states no rate. Kalshi's own help material says contract rules and the fee schedule must be checked individually for what you intend to trade. Read the current schedule for the specific contract and account type before sizing an order. A rate copied from a forum post or a third-party summary can be stale, or can describe a different market than the one on your screen. For a broader method of comparing cost structures across venues, see the fee comparison guide.

Access is a set of separate conditions, not one answer

Polymarket documents international restrictions separately from its US product, and France is restricted for international trading. A country missing from a restriction list proves neither that trading is legal there nor that promoting it is allowed: technical access, local law, product eligibility and commercial promotion are 4 different questions. Kalshi says it can accept users from many countries subject to Member Agreement restrictions, eligibility and verification, so it is neither universally accessible nor US-only. Do not assume you qualify in a given country, or in every US state, without checking the rules that apply today. If eligibility is what blocks you, the availability guide walks through it.

Put access checks before strategy work. Identity and country verification, the Member Agreement and any product-level rule each have to be satisfied on their own terms, and none of them is waived by a good price. Do not use a VPN or any other workaround to reach a restricted venue. Verify eligibility through the venue’s own process before considering a trade.

A worked mismatch: .45 versus .43 on the same question

Take an illustrative contract pair on the same headline event. Contract A resolves by a named data provider's final print at 12:00 UTC on the stated date, and sits in a category with feeRate .04. Contract B resolves by a different source and stays open until 23:59 ET that same day. Both pay 1 or 0, but they are not equivalent instruments. If A quotes .45 and B quotes .43, B is not thereby the cheaper way to own the same outcome, because the 2 contracts can disagree on the same real world event. In the last hours before A's deadline, a source change alone can flip which contract wins.

Run this as a checklist rather than a price race. 1: read both rule sets and pin down source and deadline. 2: price the fee with your real share count, using fee = C x feeRate x p x (1-p) for Polymarket and the live schedule for Kalshi. 3: add any wallet or bridge cost. 4: turn each all-in cost into an implied probability so the 2 numbers are comparable. 5: confirm eligibility and restrictions on both venues before you deposit anything. If any line stays blank, the honest outcome is no order. This pair is illustrative and is not an empirical study or a tested account.

The losing case to keep in view: you pay a fee on the taker side, the contract resolves against you, and you are out the entire premium plus costs. A .43 price is not cheap if the source or deadline you did not read is the one that decides the outcome.

Which venue fits depends on conditions, not a ranking

If a venue's documented resolution source matches your contract exactly and your eligibility is settled, then the fee math decides between near-equivalent contracts. If the only available contract rests on a source or deadline you cannot verify, no price advantage offsets that gap. If one venue is restricted where you are, the other may be the only compliant route regardless of fees. And if you are weighing other designs entirely, the alternatives guide reviews different market structures.

None of these conditions is an endorsement. Each is a reason to pick one venue for one specific contract at one specific moment.

What this comparison cannot settle for you

This is a documentary comparison. No account was opened or tested at either venue, and no fills, screenshots or account statements back it. Kalshi's numeric fee schedule is not stated here, so treat any figure you meet elsewhere as unverified until you read the live schedule. Polymarket documentation refers to USDC in some places and pUSD in newer product pages, so avoid blanket claims about collateral across products. Category rates change, and you should check each venue's contract rules for how resolution issues are handled. Nothing here predicts an outcome or promises a gain.

Your decision before the next order

Write 4 things down before you trade either venue: the resolution source and deadline for the exact contract, its category fee parameters, your share count, and your eligibility status. If any of the 4 cannot be confirmed from current official documentation, do not size the trade. If you are comparing cost structures more widely, read the fee guide; if access is the constraint, read the availability guide; if you are evaluating other market designs, read the alternatives guide. Access first, then contract rules, then fees, then price.

Side by side, illustratively

The table below sets out the illustrative pair from above. It is a documentary comparison of 2 contract documents, not a record of executed trades, and it does not rank the venues.