Kalshi vs. Polymarket: Which Prediction-Market Experience Fits Your Edge?

One light-heavyweight fight on the August 1 card sits on both venues at once. Kalshi turns it into a ticker in its KXUFCFIGHT series, settled off The Wall Street Journal, ESPN and Fox Sports. Polymarket turns it into a sentence: UFC Fight Night: Jan Blachowicz vs. Navajo Stirling. It pays both sides evenly on a no contest. Same fight, two different products.

That gap runs the whole way down. The two venues ask the same questions and share almost nothing underneath. Here is each dimension that touches your P&L, and a rule for choosing at the end.

Kalshi says it flat out: it is "regulated as a Designated Contract Market (DCM)" by the Commodity Futures Trading Commission. Polymarket is harder to pin down. Conflating its two halves is the most common mistake written about it.

A Kalshi contract is a dollar claim. It pays one dollar if the event happens, nothing if it does not. The price in between is the market's own estimate of how likely that is.

On the global Polymarket exchange your collateral sits in a wallet you control, denominated in pUSD. On Kalshi and on Polymarket US you hold a member account at a US exchange. Both fund in dollars, by card or bank transfer, with crypto on Kalshi. That difference decides how money gets in, how it gets out, and who you call when something breaks.

Pew Research Center's read on data from The Block is the cleanest independent look. Measured across roughly two years, the two venues are not trading the same thing.

Politics is the story everyone tells about prediction markets, not the story of the volume. It ran about ninety percent of Kalshi's flow in the last election cycle. Across the full window it is a low single-digit share. How the category got that big is its own piece.

Both venues price fees off the same term, P x (1 - P). Cost peaks in the middle of the range and falls away toward the tails. That shape matters more to a thin edge than the venue does.

Kalshi's current schedule charges takers round up(M x 0.07 x C x P x (1 - P)), where the multiplier defaults to one. On a standard series that lands in a band of $0.07 to $1.75 per hundred contracts.

Resting an order on a standard Kalshi series is free: the maker multiplier defaults to zero. On the global Polymarket exchange takers pay and makers never do. The rate follows the category — geopolitics is free, sports and politics sit below crypto. Polymarket US goes further and pays the maker a rebate at the trade.

Both venues run a central limit order book, so order types are not what separates them. The price grids are. Polymarket mostly quotes in whole cents; most Kalshi markets quote in tenths.

Each will also cancel every order you have resting. The triggers look nothing alike.

Headline volume misleads worst right here. A full census of both venues on one day in late July found the same shape twice.

This is where the funded model has something concrete to add. On an FPT Scale account, every position is capped at the lower of two numbers. One is your account's max open size; the other is five percent of that market's twenty-four-hour volume.

The account size you see quoted is a rule benchmark, not money to deploy. It is what your profit target, max loss and end-of-day trailing drawdown are measured against. More on funded prediction-market accounts.

Resolution costs traders more than fees do, and gets a fraction of the attention. Kalshi handles it centrally: each contract names its own rules and its own information source. A determination can take an hour, or most of a day. Polymarket's global exchange hands the job to an oracle instead.

Read the bond on the market you are trading rather than quoting the documentation. Polymarket's docs describe a typical bond of $750 in pUSD. Across the highest-volume markets we sampled, not one carried that figure. The common values were $500 and $250.

No venue wins this outright. Pick by the shape of your edge, and know the weak side going in. A zero fee is not depth, and a deep book on one venue says nothing about the same question on the other.

Neither exchange is a sportsbook, and the mechanical reasons why are worth reading first. A worked example on a fight card walks one event through as markets.

Everything above moves, which is why everything above is dated to when we read it. Polymarket changed its collateral in April and its US fee schedule in July. Before you size a trade, re-read the current fee schedule. Then read the resolution clause of the contract you intend to trade.