Last Updated: 2026-10-26
Two screens can ask almost the same question and still offer different contracts. Before comparing a price, match the outcome definition, account eligibility and cash flows. This worksheet combines the useful parts of the earlier platform rankings and reviews; it does not award a winner from unrecorded volume or personal trading claims.
Start with access to the exact product
The Polymarket geographic documentation describes location restrictions on order placement. Kalshi's international guidance points to its Member Agreement and identity/residence checks. Both were read October 26, 2026. Neither a working website nor this article establishes your eligibility. Identify the legal entity, regional product and current agreement; do not transfer assumptions between a brand's products or bypass a restriction.
For each account, record who controls credentials and funds, the supported funding asset/network, conversion and withdrawal charges, minimums and outstanding verification. A familiar stablecoin ticker is not a guarantee of redemption value or the correct network. A license, collateral mechanism or wallet label does not by itself establish deposit insurance, uninterrupted access or recovery after a loss. Leave unresolved protections unresolved.
Match the settlement question
Copy these fields side by side:
Scroll sideways to see every column. Keyboard: focus the table region and use the arrow keys.
| Field | Why it can change the result |
|---|---|
| Exact event and outcome | Winning an election, taking office and winning a party nomination are different events |
| Named source | An official release and a news projection can disagree or arrive at different times |
| Cutoff and timezone | A deadline in UTC differs from the same clock time in New York |
| Corrections and cancellation | A later revision, postponed event or void rule can produce a different payment |
| Finality and disputes | Trading close, determination and withdrawable cash are different moments |
Polymarket's resolution guide distinguishes UMA-resolved prediction markets from Chainlink TWAP up/down markets. Check the actual market's rules. Kalshi's Member Agreement likewise directs members to the individual contract terms. This page has not verified a particular cross-venue pair as equivalent.
If one contract asks whether a price touches a threshold during a month and another asks where it closes on the last day, cheaper YES plus cheaper NO is not a locked payout. Write the possible outcomes and both payments before calling a difference arbitrage. Even matching payoffs leave execution, access, settlement and counterparty risks.
Compare the same quantity at executable prices
Synthetic example, not current quotes: Venue A offers 100 YES contracts at $0.42 with a hypothetical $1.20 entry charge. Venue B offers the same assumed payoff at $0.43 with a $0.60 charge. Cash required is $43.20 versus $43.60. A $100 winning settlement produces $56.80 or $56.40 before other charges; a zero settlement loses the corresponding entry cost. There is no inferred probability of winning.
Now suppose only 20 contracts are offered at $0.42 and the next 80 cost $0.45. The purchase costs $44.40 before a separately recomputed fee. The headline price no longer describes the intended size. Cumulative volume and open interest cannot tell you which offers are executable now.
Use the cost worksheet to record fills, fees and funding costs on one basis. A resting order may never fill, or only partly fill. A limit order that immediately matches can incur taker treatment; the word “limit” is not a fee exemption. Compare the quote and actual execution, not an advertised maximum or a percent of profit against a percent of notional.
Run a no-funds review first
Save a market ID, timestamp, rules version, a sample order-book snapshot and a hypothetical order. Check what you would do if the second leg failed, the market paused, a resolution was disputed or an order acknowledgement was missing. Access to another venue does not close an inaccessible original position.
If the purpose is forecasting practice, a clearly identified play-money or nontrading forecast record may suffice. Its units and results are not dollar returns, and a good forecast does not prove profitable execution. For real-money use, retain transaction records and obtain jurisdiction/product-specific tax advice; no tax classification or income rate is established here.
Review limits and disclosure: Linked documentation checked October 26, 2026; no funded account, withdrawal, custody audit or live execution tested. These are evaluation criteria and constructed arithmetic, not a platform recommendation. AITR may receive commissions through marked links elsewhere. This comparison makes no referral offer.