[JumpCrisscross]

> can play prediction markets by betting on a swing

The outcomes are still capped. In that respect, it's more like a derivative market than the stock market. You can trade in and out of options. But the value in the system is tightly defined and, after fees, a net negative-sum game.

[kqr]

There are no fees on Polymarket. Not sure about others.

[JumpCrisscross]

> There are no fees on Polymarket

"Currently, small fees apply to Crypto and Sports markets.

Starting March 30, 2026, this will expand to include other categories like Finance, Politics, Economics, Culture, Weather, and Tech" [1].

More critically, Polymarket doesn't pay interest on deposits. (Kalshi does.)

[1] https://help.polymarket.com/en/articles/13364478-trading-fee...

[kqr]

Thanks for the correction! I have to admit it was a while since I last looked into this and I shouldn't have been so confident.

[barchar]

There is a fee implicit in the market spread. It's formed out of the time value of money w.r.t. the cost of NOT trading as well as the adverse selection faced by those with standing offers.

Increased insider trading will increase spreads.

[hunterpayne]

Then explain why the average prediction market has a smaller spread than the average equity option market.

[kasey_junk]

Depends on the event:

https://docs.polymarket.com/trading/fees