Prediction Market Volume Nears $20B as Polymarket US Takes Bigger Share
Combined volume across Kalshi and the two Polymarket venues reached $19.46 billion, with Polymarket US combinations accounting for nearly all of its weekly growth.
Prediction-market volume stayed near record levels last week, but the growth looked different this time. Kalshi still handled most of the trading, while Polymarket US added more new volume than Kalshi and pushed its share of the market higher.
Across Kalshi, Polymarket US and Polymarket International, volume reached approximately $19.46 billion from Sept. 21-27, up 3.9% from $18.72 billion the previous week.
Top-line performance notes
Total volume: Kalshi, Polymarket US and Polymarket International combined for approximately $19.46 billion, up 3.9% from $18.72 billion.
Kalshi: Weekly volume increased 2.6% to a record $15.66 billion, while Sunday set another daily high at $3.24 billion.
Polymarket US: Volume jumped 21% to $2.83 billion, increasing its share of the three-platform total from 12.5% to 14.6%.
Combination markets: Polymarket US combination contracts generated $1.53 billion, up 44.4%, and accounted for 54.1% of all volume on the platform.
Football: All 10 of the week's largest individual Polymarket US markets were football, but together they accounted for just 4.4% of total volume.
Bitcoin: Polymarket US Bitcoin volume jumped from less than $500,000 to $50.7 million, almost entirely through 15-minute and hourly markets.
Polymarket International: Volume fell 13.5% from roughly $1.11 billion to $964.1 million.
| Venue | Sept. 14-20 | Sept. 21-27 | WoW change | Share this week |
|---|---|---|---|---|
| Kalshi | $15.27B | $15.66B | +2.6% | 80.5% |
| Polymarket US | $2.34B | $2.83B | +21.0% | 14.6% |
| Polymarket International | $1.11B | $964.1M | −13.5% | 5.0% |
| Total | $18.72B | $19.46B | +3.9% | — |
Polymarket US added more volume than Kalshi
Polymarket US added $491.6 million in weekly volume. Kalshi added $395.4 million.
That doesn't change which platform is largest. Kalshi still accounted for 80.5% of the volume tracked here. But it does show where the incremental growth came from this week.
Polymarket US increased its share of the three-platform total from 12.5% to 14.6%, while Polymarket International slipped from roughly 6% to 5%.
Across all three venues, Polymarket US was responsible for roughly two-thirds of the net weekly increase.
Combinations pushed the growth on Polymarket US
Combination contracts crossed an important line this week: they accounted for more than half of all Polymarket US volume.
Volume in combinations increased from $1.06 billion to $1.53 billion, up 44.4%. Their share of Polymarket US trading jumped from 45.4% to 54.1%.
| Polymarket US | Sept. 14-20 | Sept. 21-27 | Change |
|---|---|---|---|
| Total volume | $2.34B | $2.83B | +21.0% |
| Combination volume | $1.06B | $1.53B | +44.4% |
| Non-combination volume | $1.28B | $1.30B | +1.6% |
| Combination share | 45.4% | 54.1% | +8.8 pts |
Take combinations out and Polymarket US was almost flat.
Of the $491.6 million the platform added this week, $471.2 million came from combination contracts. Everything else added only about $20 million.
That means combinations accounted for 95.9% of Polymarket US's week-over-week growth.
The impact was large enough to show up across the entire prediction-market market. Kalshi, Polymarket US and Polymarket International added a combined $736.4 million from the previous week. Polymarket US combinations alone added $471.2 million, equivalent to roughly 64% of that entire increase.
We don't yet have enough direct data to split those combinations cleanly into NFL, college football, baseball and mixed-sport contracts, so the $1.53 billion remains separate rather than being pushed back into individual sports.
Football owned the leaderboard, not the week
All 10 of the largest individual Polymarket US markets were football.
The Colts-Chiefs market led with $27.67 million, followed by Giants-Rams at $23.23 million and Falcons-Packers at $16 million. College football took six of the remaining seven spots.
| Rank | Polymarket US market | Volume |
|---|---|---|
| 1 | Indianapolis Colts vs. Kansas City Chiefs | $27.67M |
| 2 | New York Giants vs. Los Angeles Rams | $23.23M |
| 3 | Atlanta Falcons vs. Green Bay Packers | $16.00M |
| 4 | Ole Miss vs. Florida | $10.90M |
| 5 | Northwestern vs. Indiana | $9.05M |
| 6 | Clemson vs. California | $9.02M |
| 7 | Texas vs. Tennessee | $8.46M |
| 8 | Oregon vs. USC | $8.14M |
| 9 | Washington Commanders vs. Dallas Cowboys | $6.71M |
| 10 | Seattle Seahawks vs. Washington Commanders | $6.51M |
Even with football taking every spot in the top 10, those markets accounted for just 4.4% of Polymarket US volume.
The week wasn't being carried by a bunch of blockbuster games.
Most of the money was spread much wider. Polymarket US did $1.53 billion in combination volume, yet no individual combination was large enough to crack the overall top 10.
Football has been a major part of prediction-market growth since the regular season started. In Week 1, tracked NFL prediction-market volume topped $1 billion across the major venues. This week's Polymarket US numbers look a bit different: football dominates the biggest individual markets, but combination trading dominates the platform as a whole.
Tennis traded almost as much as the NFL
The NFL was the largest identifiable sports category on Polymarket US at $267 million.
Tennis was right behind it at $263.1 million.
College football added another $225.6 million, while MLB generated $201.8 million.
| Category | Sept. 14-20 | Sept. 21-27 | WoW change | Share this week |
|---|---|---|---|---|
| Combination contracts | $1.06B | $1.53B | +44.4% | 54.1% |
| NFL | $249.4M | $267.0M | +7.0% | 9.4% |
| Tennis | $262.1M | $263.1M | +0.4% | 9.3% |
| College football | $218.4M | $225.6M | +3.3% | 8.0% |
| MLB | $199.9M | $201.8M | +0.9% | 7.1% |
| Bitcoin | $0.5M | $50.7M | — | 1.8% |
| Other markets | $349.2M | $291.6M | −16.5% | 10.3% |
Traditional sports categories were not moving anything like combinations.
NFL volume increased 7%. College football gained 3.3%. Tennis was almost flat and MLB increased less than 1%.
NFL and college football combined for $492.6 million. That's less than one-third of the $1.53 billion traded through combinations.
Football dominated the individual-market leaderboard. It did not explain why Polymarket US grew 21%.
Bitcoin goes from $453,000 to $50.7 million
Bitcoin went from a rounding error to a $50 million category in one week.
Polymarket US recorded only about $453,000 in Bitcoin volume the previous week. Sept. 21-27 produced $50.7 million.
Almost all of it came from shorter-duration markets.
| Bitcoin market type | Sept. 21-27 volume |
|---|---|
| 15-minute up/down | $45.65M |
| 1-hour up/down | $4.19M |
| Other Bitcoin markets | $0.84M |
| Total | $50.69M |
Fifteen-minute markets alone generated about $45.7 million, or roughly 90% of all Bitcoin volume.
No individual Bitcoin market comes close to the biggest NFL games because the trading is split across hundreds of short windows. Added together, though, those 15-minute markets created almost the entire category.
Bitcoin still represented only 1.8% of Polymarket US volume, but the change in product mix happened almost overnight.
Every dollar of Sunday growth came from combinations — and then some
Polymarket US generated $759.8 million on Sept. 27, up from $592.2 million the previous Sunday.
Combination volume increased from $298.6 million to $468.8 million.
| Polymarket US Sunday | Sept. 20 | Sept. 27 | Change |
|---|---|---|---|
| Total volume | $592.2M | $759.8M | +$167.6M |
| Combination volume | $298.6M | $468.8M | +$170.2M |
| Other volume | $293.6M | $291.0M | −$2.6M |
Polymarket US grew by $167.6 million Sunday over Sunday. Combinations grew by $170.2 million.
Everything outside combinations was actually slightly lower.
Combinations also went from 50.4% of Sunday volume to 61.7% in one week.
More than half of Kalshi's week happened from Friday through Sunday
Kalshi increased weekly volume from $15.27 billion to $15.66 billion, adding another $395.4 million from an already enormous base.
Sunday produced $3.24 billion, setting a new daily high only seven days after Sept. 20 became Kalshi's first $3 billion day. The previous record week is covered in Sept. 14-20 volume report.
| Kalshi daily volume | Volume |
|---|---|
| Sept. 21 | $1.45B |
| Sept. 22 | $1.80B |
| Sept. 23 | $1.81B |
| Sept. 24 | $1.99B |
| Sept. 25 | $2.46B |
| Sept. 26 | $2.90B |
| Sept. 27 | $3.24B |
Friday through Sunday generated approximately $8.60 billion, or 54.9% of Kalshi's entire weekly volume.
Saturday alone reached $2.90 billion before Sunday's record. The final three days generated more trading than the first four combined.
Trade count also moved higher, from 85.26 million to 88.12 million. Our Kalshi volume page tracks the venue's daily, weekly and monthly trading history.
Polymarket US rises while International falls
The two Polymarket venues moved in opposite directions.
Polymarket US added $491.6 million during the week. Polymarket International lost about $150.6 million.
International volume fell from roughly $1.11 billion to $964.1 million, down 13.5%. Its share of volume across the three platforms slipped from about 6% to 5%.
The available International data doesn't break the decline down cleanly enough by category to say what caused it, so we aren't assigning that drop to sports, crypto, politics or another group of markets.
It does leave a clear split: one Polymarket US just had its strongest week in this dataset while the other dropped below $1 billion.
Kalshi and Polymarket US together now account for just over 95% of the volume tracked across the three platforms.
Kalshi is still the biggest part of that by far. But this week, Polymarket US was where most of the new volume showed up, and combinations were where nearly all of that growth came from.
The number to watch next week isn't whether volume crosses $20 billion. It's whether combinations remain above half of Polymarket US trading.
DeFi Rate tracks daily, weekly and monthly activity across the major venues in its prediction market volume tracker.
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