Kalshi and Polymarket US Set Records. What Do Their Volume Figures Actually Mean?

September 27 was a record day for two US prediction markets at once. According to DeFi Rate, Kalshi traded $3.2 billion in contracts, while the total value of those completed trades at their execution prices was about $704 million.

On the same day, Polymarket US set its own record: $639 million in contract volume and about $170 million at actual trade prices.

Polymarket US is a separate US-regulated venue with its own order book. It should not be confused with international Polymarket: the global venue recorded about $192 million in contract volume and $99 million at trade prices on September 27, but did not set a record that day.

Both records show rapid growth in sports prediction markets. However, billion-dollar headlines can easily be mistaken for the amount participants actually put at risk or could immediately trade at the current price. They are not the same thing.

How $3.2 Billion and $704 Million Were Calculated

A Kalshi contract pays $1 if the selected outcome occurs and $0 if it does not. Before settlement, it can trade at any price between $0.01 and $0.99.

DeFi Rate presents two different metrics:

• contract volume counts every traded contract at its $1 face value;
• value at trade prices multiplies the number of contracts by the price at which they traded.

For example, 100,000 contracts traded at $0.10 add:

• $100,000 to face-value volume;
• $10,000 to value at actual trade prices.

This calculation is performed for every trade during the day and the results are added together. Kalshi’s figures can therefore be read as follows:

• about 3.2 billion traded contracts × $1 = $3.2 billion in face-value volume;
• the sum of quantity × price across all trades = about $704 million.

The ratio gives an average price of roughly $0.22 per traded contract:

$704 million ÷ $3.2 billion ≈ $0.22

This does not mean the opposite side of each contract appeared without funding. Contracts are collateralized on both sides, and the same position may later be resold several times. Neither $3.2 billion nor $704 million therefore represents participants’ total capital or the platform’s full collateral. The key distinction is simpler: the first figure measures the face value of traded contracts; the second measures the execution-price value of one recorded side of each trade, without adding the opposite side.

Kalshi statistics and Polymarket US statistics, including DeFi Rate’s methodology.

What the Records Do Show

The difference between the metrics does not make the records meaningless. $3.2 billion on Kalshi and $639 million on Polymarket US show strong growth in trading activity, while NFL games appearing among the largest markets confirms that sports are becoming one of these platforms’ main categories.

But these figures describe completed trades, not an amount the next participant is guaranteed to execute at the current price. Order-book mechanics, spreads and slippage are covered in more detail in “From Odds to Contracts: How Prediction Markets Work”.

The records are best understood as signals of audience growth and trading activity. These figures should not, however, be compared directly with sportsbook handle or an available betting limit.