On July 21, 2026, VolRoc recorded 173,060 active prediction markets across Kalshi and Polymarket, holding $1.45B in combined open interest. Day over day, active markets rose 74.5% and open interest rose 20.3% (vs July 20, 2026). Sports was the largest domain by open interest (41%), ahead of Politics & Elections (31%); together they accounted for 73% of all open interest. Kalshi carried 76% of active markets and Polymarket 24%.
Deterministic · template v1 · 2026-07-21
As of 2026-07-21 · 00:00 UTC
Active Markets
173,060
00:00 UTC freeze
Open Interest
$1.45B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
20,444
with trading activity
Kalshi / Polymarket
76% / 24%
by active-market count
Domain Composition — 12 domains
Sports
113,448
Other
26,992
Mixed / Multi-category
16,812
Politics & Elections
6,327
Entertainment & Culture
2,566
Crypto & Digital Assets
1,932
Climate & Weather
1,183
Companies & Business
1,169
Economics & Inflation
859
Technology & AI
746
World & Geopolitics
489
Monetary Policy
454
Science & Health
83
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 = 173,060.
Largest Kalshi Series
Sports — multi-game parlays
88,715
Cross-category multi-markets
16,812
Midterm control
871
Music — artist streams
764
U.S. House races
593
Nextteamnba
444
Mlbhr
272
NFL — next team moves
254
Nextteammlb
223
Nflwins
216
Flprimary
191
Mlbtotal
182
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 July 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 — July 21, 2026.” https://volroc.ai/prediction-markets/2026-07-21/
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