Polymarket vs Kalshi vs sportsbooks

The same opinion can be expressed on a prediction market or at a sportsbook, and the venue you choose changes your expected return before you have been right or wrong about anything. Here is what actually differs.

The short version

Cost is the biggest difference

A standard −110 / −110 sportsbook line carries about 4.76% of overround. A liquid prediction market with a 1c spread on a 50c contract costs roughly 2% round trip, and often less. That gap decides how good you have to be: about 52.4% to break even at −110, versus roughly 51% on a tight order book. It sounds small. Over a season it is most of the difference between a winning and a losing record.

The one that gets least attention: account limits

Sportsbooks are not obliged to keep taking your action, and consistently winning customers routinely find their maximum stake cut to pocket change. Exchanges and prediction markets do not care whether you win — there is no house position to protect, because you are trading against other users. If you genuinely develop an edge, this eventually becomes the deciding factor rather than the pricing.

Where each one is actually best

• Polymarket — breadth. Politics, crypto, culture and a long tail of things nobody else prices. Deepest books on the major political and macro questions.
• Kalshi — US-regulated, dollar-denominated, no crypto rail. Strong on economic data, rates and weather, which are genuinely forecastable from public information.
• Sportsbooks — depth and speed on mainstream sport, plus promotions and boosts that can be worth more than the vig you are paying. Also the only place to get certain derivative markets.

Shopping across all three

If you have already decided what you want, the venue paying most is simply the venue paying most. A 3-point difference in price on the same outcome is a bigger and far more reliable edge than most people's handicapping. It requires no opinion at all — just accounts in more than one place and the discipline to check before clicking.