Polymarket US’s parlay-style Combos have quickly become a significant source of trading activity, accounting for more than one-fifth of exchange volume in each of the three most recent reporting periods.
Combo volume reached $31.4 million, or 21.6% of all Polymarket US trading, in the 24-hour period ending Sunday, up from just $2.5 million, or 1.7%, one week earlier while the product was still in beta testing and had not yet been broadly rolled out to app users.
The increase closely followed the product’s public rollout. DeFi Rate first observed the multi-leg Combo builder available to regular Polymarket US app users early Wednesday, Aug. 19. By the Aug. 21 reporting period, Combo volume had climbed above $33 million, accounting for 27.7% of all Polymarket US trading, and remained above $30 million the next two days. The rapid growth mirrors a broader shift at Kalshi, where multi-leg contracts have recently become the exchange’s largest volume category.
Trading accelerated around the public rollout
The regulatory data show Combo activity accelerating while the product was still in beta testing, then increasing sharply around the time it became available to the general public. Volume rose from $5.6 million in the reporting period ending Aug. 18 to $11 million in the Aug. 19 period, before reaching $14.1 million in the period ending Aug. 20.
| Period ending | Overall volume | Combos volume | Combos share |
|---|---|---|---|
| Aug. 16 | $147.22M | $2.46M | 1.67% |
| Aug. 17 | $101.35M | $2.02M | 1.99% |
| Aug. 18 | $105.67M | $5.59M | 5.29% |
| Aug. 19 | $124.08M | $11.04M | 8.90% |
| Aug. 20 | $133.61M | $14.14M | 10.59% |
| Aug. 21 | $119.18M | $33.03M | 27.72% |
| Aug. 22 | $147.20M | $34.46M | 23.41% |
| Aug. 23 | $145.33M | $31.38M | 21.59% |
The increase was much larger than the overall change in Polymarket US activity. From Aug. 16 through Aug. 23, total exchange volume was nearly unchanged, slipping from about $147.2 million to $145.3 million, while Combo volume increased more than 12x. That pushed Combos from a small part of trading during testing to a substantial share of exchange activity within days of the broader rollout.
DeFi Rate analyzed Polymarket US’s regulatory Time & Sales reports, which cover 24-hour periods ending at about 5 p.m. ET each day. Because those reporting periods cross calendar days, the data does not establish the exact moment the public rollout began.
Combos remain available through the Polymarket US mobile app only. Some users had reported browser trading access earlier in August, and DeFi Rate was able to access and execute a web trade for the first time Friday. The browser platform remains labeled “Beta,” and the Combo builder was still absent from the web version as of Monday.
Kalshi Combos have overtaken single-market sports
The growth on Polymarket US mirrors that on Kalshi, where its multi-leg Combos are classified in the exchange’s “Exotics” category. The product is overwhelmingly sports-focused, though a limited number of non-sports contracts can also be included in a Combo. Exotics first became Kalshi’s largest category by daily volume on June 26, overtaking its single-market Sports category for the first time this year, according to Ticker Tracker data.
Sports and Exotics traded the top spot through July and early August before Exotics moved back into first place on Aug. 7 and remained Kalshi’s largest category on every completed day through Aug. 23. From Aug. 1 through Aug. 23, Exotics generated $12.05 billion, or 42.5% of Kalshi volume, compared with $10.15 billion, or 35.8%, for single-market Sports.
That marks a notable change from July, when single-market sports contracts remained Kalshi’s largest category with about $18.95 billion in volume, compared with roughly $15 billion for Exotics. The shift in Kalshi’s volume mix offers a clear benchmark for Polymarket US, showing how quickly multi-leg trading can become a dominant source of exchange volume.
Combos can also be lucrative for exchanges
Parlay-style contracts can be valuable to prediction exchanges beyond the trading volume they generate. Sportsbooks aggressively promote parlays, which lose at high rates and are among the industry’s most profitable products because operators keep the losing stakes. Prediction exchanges do not directly profit from customers losing, but they can collect transaction fees every time a multi-leg contract trades.
In an analysis published on X Sunday, prediction market researcher Omar El Safy estimated that Kalshi earns about $4.25 for every $100 customers put up on Combos, while market makers capture roughly twice as much through their spreads. His analysis also found that the typical Kalshi Combo was priced at just 8.6 cents, with contracts below 2 cents accounting for 62.3% of Combo notional volume in August.
Combo notional volume can run far above the actual amount of customer cash involved. El Safy found that on Kalshi, $1 of cash traded generated about $11.70 of Combo notional volume, compared with about $2.30 across the rest of the exchange. Even so, the combination of growing usage and transaction fees gives exchanges a direct financial incentive to make multi-leg trading a larger part of their product mix.
Football season gives Combos their next test
The next test comes almost immediately, with the NFL regular season and college football schedule about to bring far more games into the mix. DeFi Rate found that NFL prediction-market volume reached $167.8 million across Kalshi and both of Polymarket’s exchanges (US and global) in the week ending Aug. 16, up 324.4% from the prior week, even though 85.5% of that activity came from preseason games.
That report identified Combos as the next category to watch. One week later, Polymarket US Combos are already accounting for more than 20% of exchange volume. With the main football season still ahead, the early ramp-up suggests multi-leg trading could become an even larger part of Polymarket US activity.
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