On July 28, 2026, VolRoc recorded 162,565 active prediction markets across Kalshi and Polymarket, holding $1.35B in combined open interest. Day over day, active markets rose 73.0% and open interest rose 15.6% (vs July 27, 2026). Politics & Elections was the largest domain by open interest (36%), ahead of Sports (34%); together they accounted for 70% of all open interest. Kalshi carried 78% of active markets and Polymarket 22%.
Deterministic · template v1 · 2026-07-28
As of 2026-07-28 · 00:00 UTC
Active Markets
162,565
00:00 UTC freeze
Open Interest
$1.35B
Kalshi OI + Polymarket liquidity
Markets Traded · 24h
17,789
with trading activity
Kalshi / Polymarket
78% / 22%
by active-market count
Domain Composition — 12 domains
Sports
105,040
Other
24,779
Mixed / Multi-category
16,914
Politics & Elections
6,617
Entertainment & Culture
2,694
Crypto & Digital Assets
1,743
Companies & Business
1,463
Technology & AI
1,193
Economics & Inflation
904
Monetary Policy
465
World & Geopolitics
456
Climate & Weather
212
Science & Health
85
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 = 162,565.
Largest Kalshi Series
Sports — multi-game parlays
82,444
Cross-category multi-markets
16,914
Midterm control
908
Music — artist streams
763
U.S. House races
600
Nextteamnba
474
NFL — next team moves
255
Nflwins
250
Nextteammlb
234
Mlbhr
205
Flprimary
201
Mlbhrr
183
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 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 — July 28, 2026.” https://volroc.ai/prediction-markets/2026-07-28/
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