On August 28, 2026, VolRoc recorded 241,524 active prediction markets across Kalshi and Polymarket, holding $1.81B in combined open interest. Day over day, active markets rose 7.4% and open interest rose 2.1% (vs August 27, 2026). Politics & Elections was the largest domain by open interest (32%), ahead of Sports (21%); together they accounted for 53% of all open interest. Kalshi carried 76% of active markets and Polymarket 24%.
Deterministic · template v1 · 2026-08-28
As of 2026-08-28 · 00:00 UTC
Active Markets
241,524
00:00 UTC freeze
Open Interest
$1.81B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
24,388
with trading activity
Kalshi / Polymarket
76% / 24%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
141,686
Other
41,607
Sports
36,535
Politics & Elections
10,262
Entertainment & Culture
3,344
Crypto & Digital Assets
1,832
Technology & AI
1,773
Economics & Inflation
1,011
Companies & Business
995
World & Geopolitics
926
Climate & Weather
898
Monetary Policy
527
Science & Health
128
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 = 241,524.
Largest Kalshi Series
Cross-category multi-markets
141,686
—
7,517
Midterm control
1,198
Music — artist streams
750
U.S. House races
614
Nflspread
524
Nextteamnba
512
Ncaafspread
495
Ncaafgame
371
Nflwins
360
Nfltotal
330
Ncaafwins
326
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 August 28, 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 — August 28, 2026.” https://volroc.ai/prediction-markets/2026-08-28/
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