Kalshi vs Polymarket: Fees, US Products and Trading Tools
Compare Kalshi, Polymarket international and Polymarket US without confusing their eligibility rules, fees, funding or APIs.
The useful comparison has three columns: Kalshi, Polymarket international and Polymarket US. They are separate products. Choose based on your eligibility and the exact contract, then compare executable prices, costs and tooling.
Compare the product you will actually use
| Question | Kalshi | Polymarket international | Polymarket US |
|---|---|---|---|
| Official site | kalshi.com | polymarket.com | polymarket.us |
| Fee source | Kalshi schedule and series multipliers | International market fee parameters | US product’s own fee schedule |
| Access | Current account and jurisdiction rules | International product restrictions | US product eligibility and available markets |
| Tool support | Must explicitly document Kalshi | Most tools labeled Polymarket in this directory | Must explicitly document US integration |
A federal regulatory designation does not establish eligibility for every person, location or contract. Review the current venue requirements; do not use an analytics tool’s “supported platform” label as a legal-access claim.
Compare costs on the same position
Kalshi’s general event-contract taker coefficient is 0.07, adjusted by the applicable series multiplier. Maker treatment depends on the series. International Polymarket uses market-dependent taker parameters and currently lists zero maker protocol fees. The US product needs a separate quote.
For 100 contracts at 40¢, the general Kalshi coefficient with multiplier 1 produces a $1.68 entry fee before special adjustments. An international Polymarket market using 0.05 produces $1.20. These examples do not establish which venue is cheaper for another market or trade.
The calculator supports early sales, manual charges and Kalshi’s member-specific balance precision. Compare the full order quote, including third-party costs. Avoid judging costs from a percentage label alone.
Liquidity matters at your size
Compare the bid and ask on both venues at the same time. Check how much size is actually available near those prices, and what happens to the average fill as your order grows. Total platform volume does not answer this question.
A resting order can reduce some costs but introduces non-execution and adverse-selection risk. A displayed cross-venue spread is not guaranteed arbitrage: resolution rules, funding time, fees and execution may differ.
Read both contracts before comparing odds
Confirm the same event definition, deadline, time zone and resolution source. Pay attention to cancellations, postponements, data revisions and disputed outcomes. Markets that look identical in a search result can have materially different rules.
Use the odds converter to express prices consistently, then return to the actual contracts. Normalizing a number does not normalize the underlying event.
Choose tools with documented venue support
The Kalshi tools hub covers direct API access and cross-venue research/data vendors. The Polymarket tools hub also includes wallet research and trader analytics. A wallet tool designed for international Polymarket does not automatically support Kalshi or Polymarket US.
Developers should test public reads before handling authentication or orders. Our API tutorial includes runnable read-only examples and explains missing data, pagination and rate limits.
A practical selection checklist
- Confirm your eligibility on the exact venue.
- Find the contract and read its resolution terms.
- Compare executable prices and depth for your planned size.
- Estimate entry, exit and funding costs.
- Check data/export needs and the supported API or research tool.
- Record the assumptions behind the comparison.
There is no single winner across all users and markets. Recheck the comparison when your contract, location or workflow changes.
Frequently asked questions
Is Polymarket unavailable in the US?
Polymarket US is a separate live product. International restrictions and US product eligibility must be checked separately; neither implies access to every market in every jurisdiction.
Which platform has lower fees?
It depends on the market, fee parameters, order role and third-party costs. Compare actual order quotes for the same position and include spread and slippage.
Sources & references
Primary sources used for the figures, mechanics, and regulatory statements in this guide. Where a fact is time-bound, the source date is shown — verify the latest version before relying on it for trading or compliance decisions.
- Prices and order books — Polymarket
- International trading fees — Polymarket
- Polymarket US — Polymarket US
- Official fee schedule, effective July 7, 2026 — Kalshi
- Public market-data documentation — Kalshi
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