Kalshi arbitrage calculator
Enter the two prices you can get on opposite sides of the same bet, name the venue on each side, and this works out the stake split and what the position pays once both venues have been paid.
Enter both legs
The split
| Side | Implied | Fee | Net cost | Stake | Returns |
|---|---|---|---|---|---|
| Side A | — | — | — | — | — |
| Side B | — | — | — | — | — |
- Both sides, posted
- —
- Both sides, net of fees
- —
- Margin, posted
- —
- Margin, net of fees
- —
Profit on the total stake
—
The calculation runs in your browser. Nothing you type is sent anywhere.
Two prices are not a position until both are filled. An arbitrage is a snapshot of two prices that were live moments ago, and it decays in minutes — often in seconds once either venue notices. Confirm BOTH prices at BOTH venues before staking either leg. A position with one leg filled and the other gone is not an arbitrage; it is a one-sided bet you did not intend to make. Venues also limit, void or refuse stakes at their discretion, so the profit is guaranteed by the arithmetic and by nothing else.
Why the fee field changes the answer
A standard arbitrage calculator takes two prices, converts them to implied probability, and reports whatever is left under 100%. That is the right arithmetic for two sportsbooks, because a book's margin is already inside the number it posted and there is nothing further to subtract. It is the wrong arithmetic for a prediction market, where the quote is the price two traders agreed on and the venue's cut is charged separately on top.
The gap is not academic on the positions people actually find. A two-sided position is usually worth a fraction of a percent to low single digits of the stake, and Kalshi's per-contract fee is largest exactly where those positions sit — on contracts priced near a coin flip. A calculator that ignores it will report a position on a pair that costs money to hold.
Pick the venue on each side above and this applies that venue's published schedule: Kalshi (Kalshi taker fee schedule, Jul 2026), Polymarket (Polymarket sports theta, raised 0.03 -> 0.05 Jul 2026), Novig (Novig fee schedule: pregame straights zero-fee, live takers 3%), and ProphetX (ProphetX: 2% commission on net winnings only). A sportsbook is the empty option, which means "no separate fee" and not "free" — the margin is in the price you already typed.
American odds and cents, on the same position
Kalshi and Polymarket sell contracts that settle at $1 or $0 and quote them in cents, and since August 2026 they are barred from showing American odds at all. A sportsbook shows nothing but American odds. A position across the two is therefore typed off two screens speaking two languages, which is how a leg gets entered wrong.
Each side above has its own unit, so you enter what is on the screen in front of you. A 42¢ contract is a 42% implied probability; a −110 price is 52.38%. Under the hood both become the same number, and the stake split is computed on that.
One thing the calculator cannot check for you: the two legs must be the same bet on the same line. Over 4.5 at one venue against under 5.5 at another is a middle, not a two-sided position — both legs can win, and both can lose.
In short
An arbitrage calculator takes two prices on opposite sides of the same bet at two different venues and works out how to split a stake so both sides return the same amount, net of what each venue charges. This one is the one on this term that actually subtracts a venue's fee — Kalshi, Polymarket, Novig, and ProphetX's published schedules are applied, not a generic percentage. It runs entirely in the browser; nothing typed into it is sent anywhere.
How to use this calculator
Pick each leg's venue from the selector above — a sportsbook, Kalshi, Polymarket, Novig or ProphetX — then type in the price exactly as that venue shows it: American odds for a sportsbook, cents for a contract. Both must be the same bet on the same line; the calculator has no way to check that for you, so confirm it before you type.
A worked example
Say a sportsbook prices a side at −120 and Kalshi's contract on the opposite outcome sits at 52¢. −120 implies 54.55%; 52¢ implies 52%. Added together that's 106.55% before any fee — no margin yet, just two prices that don't add to a certainty on their own. Once Kalshi's per-contract fee on that 52¢ leg is applied, the two sides can tip either side of 100%; this calculator does that arithmetic rather than leaving the fee out, which is the step most arbitrage calculators on this term skip entirely.
If the total comes out under 100%, the margin and the two stakes appear below the inputs — split in proportion to each side's own implied probability, so both legs return the same amount whichever way the outcome lands. That margin is this position's expected value: a fixed one on both outcomes at once, rather than the long-run EV a single-sided bet carries, which is the difference between arbitrage and everything else on this site.
Two things this calculator cannot catch for you. First, whether the two legs will still be there once you place them — a Kalshi or Polymarket quote is only good for the size resting behind it, and a sportsbook can reprice between your two clicks. Second, whether the venue you picked has a published fee at all: a sportsbook's answer is always "none separate," because its margin already lives inside the price you typed, not because it's free to bet there.
Check the live arbitrage board for positions the scan has already found rather than typing in prices by hand, or Kalshi vs DraftKings arbitrage for how this works between one specific pair of venues, fees and overlap included. A no-vig calculator answers a different question — the fair price under one market, not a stake split across two of them — and is the right tool when you have one book's price rather than two venues' prices on the same bet.
Arbitrage calculator FAQ
What is a Kalshi arbitrage calculator?
A calculator that splits a stake between a Kalshi contract and an opposite price elsewhere, net of Kalshi's own per-contract fee. A generic arbitrage calculator divides the two posted prices and stops there, which overstates the margin on any Kalshi leg because the fee is charged separately, on top of the quote.
How does an arbitrage calculator work?
It converts both prices to implied probability and adds them together. If the total is below 100%, the shortfall is the margin, and each leg's stake is its own implied probability divided by the total so both legs return the same amount whichever side wins.
How do I split my stake between two venues?
In proportion to what each side costs. A side implying 47% of a certainty takes 47 parts of the stake and a side implying 51% takes 51, so the two returns come out equal. This calculator does that split net of each venue's fee, which shifts it slightly toward the venue that charges more.
Does this arbitrage calculator include Kalshi fees?
Yes. Selecting Kalshi on either side applies its published per-contract trading fee, which is a curve that peaks near 50 cents and shrinks toward both extremes, including Kalshi's rounding of the fee up to the whole cent.
How do I enter a Kalshi or Polymarket price?
Switch that side's unit to cents and enter the contract price, for example 42 for a 42-cent contract. Prediction markets are barred from displaying American odds, so cents is what their screens show.
What is a good arbitrage margin?
On public venues, a fraction of a percent to low single digits of the total staked. A figure above roughly eight percent almost always means the two legs are not the same bet, one price is stale, or a market is settling a different outcome under a similar name.
Can an arbitrage lose money?
Yes, in three ways this calculator can show you and one it cannot. It can be negative once fees are applied; the stake split can be wrong; and the two legs can be different lines. The one it cannot see is a leg that fails to fill, which leaves a one-sided bet rather than a position.