Kalshi vs Polymarket: Will the rate of CPI inflation be above 3.9% for the year ending in August 2026

Last observed 2026-09-04 20:08 UTC. Prices and fees change constantly; the rules comparison is the durable part.

• SETTLEMENT_POLICY_MISMATCH — both venues publish settlement policy, but the published texts diverge
• REVISION_POLICY_MISMATCH — the venues publish different rules about data revisions
• SETTLEMENT_GUARANTEE_UNKNOWN — the venue does not publish enough settlement policy to prove what happens in every branch (missing data, cancellation, revision)

Capital lock-up: about 97.7 days until the later of the two contracts settles.

Kalshi fine-print grade: F (35/100)
−20 FAMILY_POLICY_INCOMPLETE: the rules omit terms this contract family requires — the measurement basis, the revision rule, or the missing-release branch its peers publish
−20 MISSING_CANCELLATION_POLICY: the rules never say what happens to open positions if the event is canceled, voided, or never takes place
−15 MISSING_REVISION_POLICY: the rules never say whether a later revision of the underlying number changes the outcome
−10 MISSING_NEGATIVE_BRANCH: the rules say what settles the contract Yes but never state what settles it No

Polymarket fine-print grade: C (60/100)
−20 CONFLICTING_AUTHORITATIVE_SOURCE: the rules name more than one authoritative source, and those sources can disagree with each other
−20 MISSING_CANCELLATION_POLICY: the rules never say what happens to open positions if the event is canceled, voided, or never takes place

What Kalshi publishes

If the Consumer Price Index (CPI) increases by more than 3.9% in the twelve months ending August 2026 (as represented by the one-decimal place value reported by the Bureau of Labor Statistics), then the market resolves to Yes. In the case of a delay in data caused by a federal government shutdown impacting the reliability of the Source Agency, the market’s latest Expiration Date will be extended to the sooner of the release of the Underlying or six months after the end of the government shutdown

What Polymarket publishes

This market will settle to Yes if U.S. inflation, before seasonal adjustment, over the 12-month period ending in August 2026 (CPI YoY) is above 3.9%. Outcome sourced from BLS. Settlement is based on the Consumer Price Index release published by the Bureau of Labor Statistics (BLS), currently scheduled for release on September 11, 2026. Any subsequent revisions to this figure will not be considered for settlement purposes. If the BLS does not publish CPI YoY for August 2026 on the Consumer Price Index scheduled release date, the first figure officially published by BLS for CPI YoY in August 2026 will be used for settlement. If no qualifying figure is published within three months of the scheduled release date, this market will resolve based on data from the most recent previous month with available data.

Fees use each venue's published taker formula at the last observed price — see the fee calculator for any price.