Prediction Market Volume Reaches $120.7 Billion in October, Up 64%
Per DeFi Rate volume tracker, Kalshi generated $98.2 billion in October trading volume, while Polymarket US reached $14.8 billion. Underdog and Novig more than doubled their monthly volume as combo trading continued to expand across exchanges.
U.S. prediction market volume reached $120.73 billion in October 2026, up 64.1% from $73.58 billion in September, according to DeFi Rate's analysis of trading activity across eight exchanges.
Kalshi led with $98.15 billion, accounting for 81.3% of reported volume, followed by Polymarket US at $14.77 billion. Together, the two exchanges generated $112.92 billion, or 93.5% of the October total.
October's growth extended beyond the two market leaders. Novig and Underdog more than doubled their monthly trading volume, while identified combo volume across five exchanges increased 93.2% to at least $79.46 billion.
The industry's reported volume increased by $47.15 billion month over month, with Kalshi accounting for $37.30 billion of that growth.
October prediction market volume: Key takeaways
Total reported volume reached $120.73 billion, increasing 64.1% from September across eight exchanges.
Kalshi led with $98.15 billion, up $37.30 billion, accounting for 81.3% of reported activity.
Polymarket US reached $14.77 billion, up 69.8%, and slightly increased its share of reported volume.
Underdog and Novig led percentage growth, rising 174.7% and 126.1%, respectively.
Identified combo volume reached at least $79.46 billion, growing 93.2% across five exchanges.
October 25 was the busiest Sunday for Kalshi, Polymarket US, Novig and Underdog, with identified combos accounting for most of the increase over other October Sundays.
October prediction market trading volume by exchange
Six of the eight exchanges in DeFi Rate's analysis recorded monthly trading growth. Kalshi remained the largest by a significant margin, while Polymarket US, Novig and Underdog grew faster in percentage terms.
| Exchange | October volume | September volume | MoM change |
|---|---|---|---|
| Kalshi | $98.15B | $60.85B | +61.3% |
| Polymarket US | $14.77B | $8.70B | +69.8% |
| Novig | $3.27B | $1.45B | +126.1% |
| Crypto.com / Nadex | $2.19B | $1.56B | +40.3% |
| Underdog Exchange | $1.98B | $721.5M | +174.7% |
| ProphetX | $306.3M | $240.7M | +27.3% |
| Gemini Titan | $42.1M | $44.1M | −4.4% |
| ForecastEx | $14.4M | $19.5M | −26.3% |
| Total | $120.73B | $73.58B | +64.1% |
Source: DeFi Rate analysis of exchange trading reports. The total includes eight exchanges with available September and October figures. Underdog figures represent its own exchange, not trades routed to third-party venues.
Kalshi and Polymarket US accounted for nearly all reported trading activity, but their combined share fell slightly as smaller exchanges grew faster.
Kalshi's share fell from 82.7% in September to 81.3% in October. Polymarket US increased its share from 11.8% to 12.2%, while Novig rose from 2.0% to 2.7%. Polymarket US had already recorded a 21% weekly volume jump to $2.83 billion during Sept. 21-27, 2026, according to DeFi Rate's earlier weekly report.
Underdog also gained share, increasing from approximately 1.0% to 1.6%.
These shares represent the eight exchanges covered in the analysis, not the entire U.S. prediction market industry. Complete October totals were unavailable for several additional exchanges, including CME Group, ICE Futures U.S. and DKeX/Railbird.
Kalshi adds $37.3 billion in October trading volume
Kalshi trading volume in October reached $98.15 billion, up 61.3% from September's $60.85 billion.
The exchange accounted for approximately 79% of the total monthly volume increase across the eight reporting venues.
Its largest trading day was Oct. 24, when volume reached $5.30 billion. Kalshi also generated $4.77 billion the following day, its highest-volume Sunday of the month.
Combo trading represented a substantial portion of Kalshi's October activity. DeFi Rate identified at least $66.86 billion in combo volume, compared with $35.49 billion in September.
That represents an 88.4% increase in identified combo volume, substantially faster than Kalshi's overall monthly growth.
Identified combos accounted for at least 68.1% of the exchange's October volume, compared with 58.3% in September.
Kalshi's volume excluding those identified combos increased from approximately $25.36 billion to $31.29 billion. That remainder includes any combo contracts not captured by the verified classifications, so it cannot be treated as a fully certified standalone volume total.
Polymarket US grows nearly 70% to $14.77 billion
Polymarket US trading volume reached $14.77 billion in October, up 69.8% from $8.70 billion in September.
The exchange added $6.07 billion in monthly trading activity, the second-largest absolute increase among the eight exchanges.
Polymarket US also gained share against Kalshi, accounting for 12.2% of reported volume, up from 11.8% in September.
Identified combo volume rose from $3.91 billion to $8.60 billion, up about 120%. Combos accounted for at least 58.2% of the exchange's October volume, compared with 45.0% in September.
The figures show that identified combo trading expanded considerably faster than Polymarket US's overall activity.
Oct. 25 was the exchange's largest reported trading day of the month, reaching $830.9 million.
Novig and Underdog more than double monthly volume
Underdog trading volume recorded the fastest percentage growth among the eight exchanges, increasing 174.7% to $1.98 billion.
Its September volume was $721.5 million, meaning the exchange added $1.26 billion during October.
At least $1.54 billion of Underdog's October volume came from combos, representing 77.9% of its total trading activity. That was the highest identified combo share among the five exchanges included in the combo analysis.
Novig trading volume followed with 126.1% growth, increasing from $1.45 billion in September to $3.27 billion in October.
The exchange added $1.82 billion in monthly volume, surpassing Underdog by approximately $1.29 billion.
Novig's trading activity was nearly evenly divided between combos and standalone contracts:
Combos: $1.61 billion, representing 49.3% of October volume.
Standalone contracts: $1.66 billion, representing 50.7%.
Novig reported approximately 11.33 million trades in October under its published trade-count methodology.
Both exchanges reached their highest-volume day of October on Oct. 25. Novig generated $208.7 million, while Underdog reached $144.6 million.
Combo trading reaches at least $79.46 billion in October
Identified combo volume across Kalshi, Polymarket US, Novig, Underdog and Crypto.com/Nadex reached $79.46 billion in October, increasing 93.2% from $41.13 billion in September.
The increase of approximately $38.33 billion was concentrated heavily at Kalshi, which accounted for $31.37 billion of the additional identified combo volume.
Polymarket US contributed another $4.69 billion in growth.
| Exchange | September combos | October combos | October combo share |
|---|---|---|---|
| Kalshi | $35.49B | $66.86B | ≥68.1% |
| Polymarket US | $3.91B | $8.60B | ≥58.2% |
| Novig | $619.9M | $1.61B | 49.3% |
| Underdog | $608.2M | $1.54B | ≥77.9% |
| Crypto.com / Nadex | $500.0M | $837.8M | 38.3% |
| Total | $41.13B | $79.46B |
Source: DeFi Rate analysis. Combo figures for Kalshi, Polymarket US and Underdog represent identified contract-family minimums. Novig and Nadex figures use their verified product classifications.
Combo volume grew faster than overall trading activity at Kalshi, Polymarket US, Novig and Underdog.
The increase also changed the composition of exchange volume. At Kalshi, identified combos represented 68.1% of October trading, up from 58.3% in September. Polymarket US's identified combo share increased from 45.0% to 58.2%.
Novig's combo volume increased approximately 160%, while Underdog's identified combo volume rose approximately 154%.
Combos can generate substantially more reported contract volume than a similarly priced standalone trade because multiple outcomes are combined into a single contract. As a result, contract volume should not be interpreted as the cash traders spent or the revenue an exchange earned.
The combined figures establish how quickly combo trading expanded in October, although the incomplete classification of some contract families prevents a definitive industry-wide standalone-versus-combo comparison.
October 25 records the highest Sunday volume across four exchanges
October 25, was the highest-volume Sunday of the month for Kalshi, Polymarket US, Novig and Underdog.
Each exchange exceeded its average volume for the other three October Sundays.
| Exchange | October 25 volume | Above other Sunday average |
|---|---|---|
| Kalshi | $4.77B | +21.7% |
| Polymarket US | $830.9M | +20.6% |
| Novig | $208.7M | +16.5% |
| Underdog | $144.6M | +51.0% |
Underdog recorded the largest percentage increase relative to its other October Sundays, followed by Kalshi and Polymarket US.
Identified combo trading accounted for most of the additional volume at all four exchanges.
At Polymarket US, changes in identified combo activity accounted for 99.8% of the increase above its other-Sunday average. The corresponding figures were 89.5% at Kalshi, 84.9% at Underdog and 67.1% at Novig.
Kalshi was the only exchange among the four whose highest-volume day occurred on Saturday, October 24, rather than Sunday.
Its Saturday total exceeded Sunday's by $530.8 million, with $512.1 million of that difference attributable to higher identified combo volume.
NFL contracts appeared among the most-traded named markets that weekend. Kalshi recorded $45.5 million in volume on a Kansas City versus Seattle winning-outcome contract, while a six-player touchdown combo generated $21.7 million on Sunday.
However, the available contract classifications do not establish that NFL trading accounted for most of the October 25 volume across these exchanges.
The findings show that October 25 was an unusually active Sunday relative to the other October Sundays, with combo activity accounting for most of the increase.
Crypto.com and ProphetX grow as Gemini and ForecastEx decline
Crypto.com Derivatives North America, operating through Nadex, generated $2.19 billion in October trading volume, up 40.3% from September.
Identified combo trading reached $837.8 million, representing 38.3% of the exchange's monthly activity.
ProphetX also grew, increasing 27.3% to $306.3 million.
Two exchanges moved in the opposite direction.
Gemini Titan's volume declined 4.4% to $42.1 million, while ForecastEx fell 26.3% to $14.4 million.
Combined, the two declining exchanges accounted for less than 0.05% of the October volume covered by DeFi Rate's analysis.
The difference in performance was substantial. While total reported trading expanded 64.1%, Novig and Underdog posted triple-digit increases, and the smallest exchanges did not all participate in the broader growth.
Methodology
DeFi Rate analyzed September and October 2026 trading reports covering Kalshi, Polymarket US, Novig, Crypto.com Derivatives North America/Nadex, Underdog Exchange, ProphetX, Gemini Titan and ForecastEx.
Trading volume is presented in U.S. dollars under the $1-per-reported-contract or native-volume-unit convention. The figures measure reported volume rather than cash exchanged at execution price. Individual exchanges may use different business-day reporting boundaries.
Exchange market share is calculated using the eight reporting venues, excluding exchanges without complete available monthly figures. Volume is attributed to the exchange where the trade occurred, avoiding double-counting of orders routed through third-party apps.
Combo figures for Kalshi, Polymarket US and Underdog reflect identified contract-family minimums. Novig and Nadex figures use verified product-level classifications. Unclassified contracts are not automatically assigned to standalone trading.
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