On August 21, 2026, VolRoc recorded 180,670 active prediction markets across Kalshi and Polymarket, holding $1.64B in combined open interest. Day over day, active markets fell 1.4% and open interest rose 10.0% (vs August 20, 2026). Politics & Elections was the largest domain by open interest (35%), ahead of Sports (25%); together they accounted for 60% of all open interest. Kalshi carried 70% of active markets and Polymarket 30%.
Deterministic · template v1 · 2026-08-21
As of 2026-08-21 · 00:00 UTC
Active Markets
180,670
00:00 UTC freeze
Open Interest
$1.64B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
23,525
with trading activity
Kalshi / Polymarket
70% / 30%
by active-market count
Domain Composition — 12 domains
Mixed / Multi-category
90,459
Sports
35,248
Other
33,657
Politics & Elections
9,997
Entertainment & Culture
2,977
Crypto & Digital Assets
1,934
Technology & AI
1,711
Climate & Weather
1,310
Economics & Inflation
999
Companies & Business
958
World & Geopolitics
840
Monetary Policy
471
Science & Health
109
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 = 180,670.
Largest Kalshi Series
Cross-category multi-markets
90,459
Sports — multi-game parlays
2,032
—
1,516
Midterm control
1,134
Music — artist streams
769
U.S. House races
612
Nextteamnba
508
Nflspread
414
Nflwins
350
Primary vote shares
347
Nfltotal
293
Ncaafwins
277
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 21, 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 21, 2026.” https://volroc.ai/prediction-markets/2026-08-21/
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