On September 22, 2026, VolRoc recorded 233,607 active prediction markets across Kalshi and Polymarket, holding $1.76B in combined open interest. Day over day, active markets rose 10.1% and open interest rose 158.7% (vs September 21, 2026). Politics & Elections was the largest domain by open interest (33%), ahead of Sports (20%); together they accounted for 53% of all open interest. Kalshi carried 85% of active markets and Polymarket 15%.
Deterministic · template v1 · 2026-09-22
As of 2026-09-22 · 00:00 UTC
Active Markets
233,607
00:00 UTC freeze
Open Interest
$1.76B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
21,891
with trading activity
Kalshi / Polymarket
85% / 15%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
160,202
Other
28,197
Sports
25,684
Politics & Elections
9,988
Entertainment & Culture
3,001
Crypto & Digital Assets
1,622
Technology & AI
1,344
Economics & Inflation
1,021
Companies & Business
870
World & Geopolitics
781
Monetary Policy
491
Climate & Weather
289
Science & Health
117
Venue-agnostic subject taxonomy from Kalshi series prefixes and
Polymarket title keywords. A residual Other bucket is reported honestly.
Yes-price across both venues, 10 buckets from 0 to 100. n = 233,607.
Largest Kalshi Series
Cross-category multi-markets
147,110
KXMVECROSSCATEGORY0
13,092
Midterm control
1,479
Votegeneral
1,209
Music — artist streams
668
U.S. House races
651
Ncaafspread
458
Ncaafwins
434
Nextteamnba
425
Nflwins
402
Midtermvoteturn
297
Ncaaftotal
282
Kalshi market families (Polymarket is not series-structured).
About & Citation
This is the fixed-hour (00:00 UTC) state of every active market on
Kalshi and Polymarket for September 22, 2026. The live
Observatory
shows the current diurnal value; this record is immutable. Open interest combines Kalshi
open interest with Polymarket USD liquidity as comparable USD magnitudes. Sources: Kalshi, Polymarket.
How to cite
“VolRoc Prediction Market Archive — September 22, 2026.” https://volroc.ai/prediction-markets/2026-09-22/
Get the daily statistics
A short daily read on the prediction-market universe across Kalshi and Polymarket.
Join the list →