Kalshi vs. a Sportsbook: What Each One Actually Costs

By Alex Thornton · author of the MIT-licensed teachersbettextbook library · Last reviewed 24 July 2026

“Exchanges are cheaper” is a slogan, not a number. Put both venues in the same units — the cost of one identical claim — and the answer flips depending on the spread and the price. Here is the arithmetic, including the half nobody quotes.

A Kalshi trade costs half the bid–ask spread you cross plus an explicit per-contract fee; a sportsbook trade costs the overround baked silently into its posted price. Priced apples to apples on a claim that pays $100, a taker crossing a 2¢ spread near even money pays $2.75 against a −110 book’s $2.38.

Put both in the same units

You cannot compare “−110” to “51¢” by staring at them. Convert both into the price of the same object: a claim that pays $100 if your side wins. On a market whose fair probability is 50%, that claim is worth $50. Everything above $50 is what the venue charged you.

where:

• $C$ — contracts (100 here, since each pays $1 and we want a $100 claim).
• $P$ — the price you trade at, in dollars.
• $s$ — the bid–ask spread in dollars. A taker pays $s/2$ per contract above the midpoint.

Every row is measured against the same $50 fair value: outlay above fair is what you hand over minus the $50 the claim is worth, and cost is that plus the fee. The book itemises no fee — its whole charge is inside the $52.38 price. Contracts are 100 throughout.

Read the two $2.75 rows again, because they are the sentence the exchange marketing never contains: a taker crossing a 2¢ market near a coin flip pays more than a −110 book — and so does a taker on a 1¢ market quoted 50/51, because both trades fill at the same 51¢ ask. Kalshi ticks in whole cents, so a 1¢ market cannot straddle a 50¢ fair value; it sits a tick to one side, and which side it sits on is worth a full cent per contract. The exchange’s advantages are real, but they live in the last two rows — a 1¢ market whose ask is the fair price, a resting order, a position held to settlement, or a price away from 50¢.

Exactly how tight the market has to be

The comparison has a closed form. An exchange taker beats a book when the half-spread plus the fee is smaller than what the book charges on that side:

Hold the right-hand side at the −110 baseline of 2.38¢ and solve for the widest market that still wins:

That closed form assumes the midpoint sits exactly on fair value, which whole-cent ticks will not allow at 50¢. The two realizable 1¢ quotes are 49/50 and 50/51, and only the first clears the bar: its 50¢ ask is the fair price, so the taker pays the $1.75 fee and nothing above fair. The second fills at 51¢ for $2.75 — identical to a 2¢ market. So “1.26¢ wide” is not a quote you can go and find at a 50¢ fair value; it is the continuous bar, and the two quotes above are what actually clears or misses it. Away from 50¢ the allowance widens fast, because the fee is shrinking while the book’s charge is not.

One honesty note on that table: 2.38¢ is the right baseline near even money and the wrong one at the tails. A real book at 90/10 does not charge 2.38¢ on both sides. The next section prices a real one.

The inverted fee shape, on a real line

The two venues load their costs onto opposite ends of the price range, and this is the part that decides most comparisons. Consider a big NFL favorite quoted −450 / +340:

Split that overround with the power method, which corrects favorite–longshot bias rather than assuming the book spread its margin evenly:

Now the same game on an exchange, fair 80¢ / 20¢, market 1¢ wide. The fee does not care which side you take — $P(1-P)$ is symmetric:

Line them up: on the favorite the book charges 1.9% and the exchange taker 2.0% — a tie, inside the noise. On the underdog the book charges 13.2% and the exchange 8.1%. The exchange’s edge is not general cheapness; it is concentrated exactly where the book’s pricing is most aggressive.

And a warning that belongs in the same breath: cheap longshots are not good longshots. A 2026 study of 300,000+ settled Kalshi contracts found low-priced contracts winning less often than their fee-adjusted break-even required.^[2] A lower cost on a systematically shaded price is still a loss. Nothing here says which side of anything to take.

Where the sportsbook wins

Four cases, stated plainly, because a comparison that only runs one direction is marketing.

1. A thin contract. The single biggest cost on an exchange is not the fee, it is the spread on a market nobody is trading. A 12¢-wide book — bid 44, ask 56, midpoint 50 — costs a taker:

2. Small orders pay a rounding surcharge. The fee is rounded up to the next cent on the whole order. One contract at 90¢ owes 0.63¢ by formula and pays a full penny — 59% above rate. On 100 contracts the rounding is noise; on 3 contracts it is the dominant term.

3. Boosts and promotional prices. A book that prices a specific market above its normal line is genuinely reducing the cost of that specific claim, and exchanges have no equivalent instrument. Where such a price exists, it enters this arithmetic like any other price: convert it, compare it, and the comparison is whatever it is.

4. Markets that only exist at a book. Player props, alternate lines and correlated multi-leg tickets have no contract equivalent on the exchange. A comparison is only defined where both venues list the same claim; everywhere else, the book is not more expensive, it is the only venue.

Where the exchange wins

Settlement is free, so patience is subsidised. Fees are charged per trade and resolution charges nothing, which makes the exit path a fee decision:

Makers are paid to wait. A resting order pays roughly a quarter of the taker rate and skips the spread entirely — 44¢ on a $100 claim against the book’s $2.38 — at the cost of an uncertain fill. Note that some major events instead carry a flat 0.25% maker fee, which is trivial at 50¢ and a real bite on a sub-5¢ contract.^[1]

Winning accounts are not a liability. A book profits when you lose, so it limits or bans consistent winners; a capped stake turns any percentage edge into pocket change. An exchange earns its fee whichever side wins.

Depth is visible. A posted line hides how much money stands behind it. An order book tells you exactly how many contracts sit at each price — and therefore what your own size will cost you.

The comparison table

The regulatory row is a live question, not a settled fact — several state gaming regulators have contested whether sports event contracts fall under their statutes, exchanges have contested those orders in federal court, and rulings have gone different ways. The prediction-markets primer lays out what is settled and what is not. This page is arithmetic about cost, not legal advice.

Or price the fee on its own with the Kalshi fee calculator, and compare a book’s posted line with the no-vig calculator.

Sources

1. Kalshi. “Fee Schedule” (July 2026 revision). — taker and maker formulas, the round-up-to-the-cent rule, the flat 0.25% maker case, and the zero settlement fee.
2. Burgi, C., Deng, W. & Whelan, K. (2026). “Makers and Takers: The Economics of the Kalshi Prediction Market.” GWU Working Paper 2026-001. PDF. — 300k+ settled contracts: informative prices, favorite–longshot bias after fees.
3. Shin, H. S. (1993). “Measuring the Incidence of Insider Trading in a Market for State-Contingent Claims.” The Economic Journal 103(420), 1141–1153. — why a book’s overround is not split evenly between the two sides.
4. Thaler, R. H. & Ziemba, W. T. (1988). “Anomalies: Parimutuel Betting Markets: Racetracks and Lotteries.” Journal of Economic Perspectives 2(2), 161–174.

Every formula here lives on the Formula Sheet for quick reference.