# Polymarket vs Kalshi: the Gap After Fees

The matched Fed contracts Vultax already compares, with the raw price difference and what survives each venue’s own published fee.

Canonical: https://vultax.com/features/prediction-market-arbitrage
JSON: https://vultax.com/features/prediction-market-arbitrage/data.json

Availability: The matched-contract comparison on this page is published by Vultax and free to read. Inside the app, cross-venue deviance is a watch-only signal, not an execution tool.

## The Polymarket–Kalshi gap, before and after fees

The same matched contract on both venues, with the raw difference and what is left once each venue’s own fee is applied.

Status: fresh. Within this table’s source-time freshness window; prices can change between observations.
Source observed at: 2026-09-14T06:10:02.000Z
Coverage: Only the reviewed Fed meeting and contract combinations shown. Prices are percentages of a $1 payout; a gap is not an executable return.

| Meeting | Contract | PM − Kalshi (percentage points) | After venue fees (percentage points) | Polymarket 24h volume (USD) | Kalshi 24h volume (USD) | Kalshi open interest (USD) |
| --- | --- | --- | --- | --- | --- | --- |
| September | 25 bp increase | 2 | 0 | 1756546 | 2382394.6799999997 | 33265250.98 |
| September | No change | -1 | 0 | 2289560 | 2382394.6799999997 | 33265250.98 |
| September | 25 bp decrease | -0.2 | 0 | 1958889 | 2382394.6799999997 | 33265250.98 |
| October | 25 bp increase | -1 | 0 | 30481 | 16765.45 | 415239.30000000005 |
| October | No change | 1 | 0 | 7805 | 16765.45 | 415239.30000000005 |
| October | 25 bp decrease | -0.2 | 0 | 21986 | 16765.45 | 415239.30000000005 |
| December | 25 bp increase | 0.5 | 0 | 10842 | 3794.58 | 104040.85 |
| December | No change | -3.5 | 1.5 | 9986 | 3794.58 | 104040.85 |
| December | 25 bp decrease | 0.2 | 0 | 7602 | 3794.58 | 104040.85 |

- The after-fee column applies the source pack’s assumed fee of 2 percentage points across the pair. Real fees depend on your account, order type and the venue’s current schedule.
- Volume and open interest are reported per meeting by each venue, not per contract row.
- Depth, transfer time, settlement wording and account access are not in this calculation. A remaining gap is a reason to look, not an executable trade.
- Source: [Vultax prediction pack · Polymarket Gamma and Kalshi](https://vultax.com/live/prediction.json)
- [JSON](https://vultax.com/features/prediction-market-arbitrage/data.json?dataset=cross-venue-fee-adjusted) · [CSV](https://vultax.com/features/prediction-market-arbitrage/data.csv?dataset=cross-venue-fee-adjusted)

## Fed contract prices: Polymarket and Kalshi

The matching contract rows already assembled by Vultax’s prediction pack.

Status: fresh. Within this table’s source-time freshness window; prices can change between observations.
Source observed at: 2026-09-14T06:10:02.000Z
Coverage: Only the Fed meeting/contract combinations shown. Prices are percentages of a $1 payout; they are not forecasts of guaranteed outcomes.

| Meeting | Decision date | Contract | Polymarket (%) | Kalshi (%) | PM − Kalshi (percentage points) |
| --- | --- | --- | --- | --- | --- |
| September | 2026-09-16 | 25 bp increase | 79.5 | 77.5 | 2 |
| September | 2026-09-16 | No change | 20.5 | 21.5 | -1 |
| September | 2026-09-16 | 25 bp decrease | 0.35 | 0.5 | -0.2 |
| October | 2026-10-28 | 25 bp increase | 36.5 | 37.5 | -1 |
| October | 2026-10-28 | No change | 61.5 | 60.5 | 1 |
| October | 2026-10-28 | 25 bp decrease | 3.25 | 3.5 | -0.2 |
| December | 2026-12-09 | 25 bp increase | 57.5 | 57 | 0.5 |
| December | 2026-12-09 | No change | 39.5 | 43 | -3.5 |
| December | 2026-12-09 | 25 bp decrease | 2.7 | 2.5 | 0.2 |

- Polymarket Gamma prices and Kalshi bid/ask midpoint or last-price fallback come from the source pack. They are collected sequentially.
- Contract wording, settlement terms, fees and available depth must be checked at each venue. A displayed gap is not an executable arbitrage return.
- The pack’s asOf records the parent Fed-pack refresh, not an exchange tick timestamp. Failed parent components can retain older observations.
- Source: [Vultax prediction pack · Polymarket Gamma and Kalshi](https://vultax.com/live/prediction.json)
- [JSON](https://vultax.com/features/prediction-desk/data.json?dataset=fed-contract-comparison) · [CSV](https://vultax.com/features/prediction-desk/data.csv?dataset=fed-contract-comparison)

## Related research

- [Why Most Crypto Arbitrage Spreads Are Not Executable](https://vultax.com/research/why-crypto-arbitrage-spreads-are-not-executable) — published 2026-09-02
- [We Tested Polymarket Prices Against 6,776 Resolved Markets. Here's Where They Bend.](https://vultax.com/research/prediction-market-fair-value-calibration) — published 2026-09-08

Continue: [Open the prediction desk](https://app.vultax.com/predictions)

- Public tables mirror existing Vultax source packs. They do not include account data, private watchlists or the complete app dataset.
- Source time, coverage and limitations apply to each table. Missing values are unavailable, not zero.