Kalshi–Polymarket Sports Arbitrage: A Practical US Workflow

Kalshi–Polymarket sports arbitrage starts with matching the same sporting outcome across venues, then checking whether complementary positions cost less than their combined payout after applicable costs. For the US workflow discussed here, Polymarket means Polymarket US. Novig is a third venue to compare when it lists an equivalent market.

The arithmetic is simple. The difficult parts are matching the contracts, buying at the displayed prices, and completing both sides. A price gap is a candidate to investigate, not a finished trade.

TurbineFi Sports is launching to help organize that comparison across Kalshi, Polymarket US, and Novig. We make the product. This guide explains a manual execution process, with illustrative numbers rather than observed opportunities or promised returns.

View TurbineFi Sports pricing if these are the venues you want to compare. Start with the checks below before acting on any displayed spread.

What a two-outcome arbitrage actually requires

Suppose a contract pays $1 if a particular team wins and $0 otherwise. A complementary position must cover every case in which that contract does not pay, under equivalent settlement rules.

If one side costs $0.47 and the other costs $0.50, the combined price is $0.97 for a $1 combined payout. That leaves $0.03 per matched pair before fees and other costs.

The word “complementary” carries most of the work. Two markets can name the same teams and still describe different events. They may handle overtime differently, use different spread lines, or apply different rules after a postponement. A third outcome may exist that you have not covered.

Verify the complete outcome set before calculating a return. If you cannot explain why exactly one position pays in every permitted settlement scenario, you have not established the intended hedge.

Start with one exact sports market

Begin with a full-game winner, an identical half-point spread, or an identical half-point total. These are easier to compare than a mixture of periods, alternative lines, and player statistics.

For a total, write down the number. Over 221.5 and under 222.5 are not exact opposites. For a spread, write down the team and sign. A home favorite at −5.5 must be paired with the complementary +5.5 proposition, not simply any quote associated with the away team.

Check the scheduled event date and participants as well. Similar names, recurring matchups, and series markets can make a superficially plausible match wrong.

Use the market's full wording and settlement terms, not a shortened label in a comparison screen. The screen should help you locate a candidate; the venue's contract defines the position you buy.

Keep Polymarket US distinct

Do not transfer a price, fee assumption, balance, or market identifier from international Polymarket into a Polymarket US calculation. Treat the specific venue as part of the contract's identity.

This matters when following tutorials and screenshots. A guide may use “Polymarket” loosely even though its example comes from a different product. Before applying its numbers, check which venue supplied the quote and which account would hold the position.

For this workflow, record three separate venue labels: Kalshi, Polymarket US, and Novig. If you compare another venue later, add it explicitly rather than silently reusing the same column.

Availability and account eligibility must also be checked with each venue. Do not infer your access from the fact that a market appears in a comparison tool.

Calculate the spread after applicable fees

For equal quantities of two complementary $1-payout contracts:

Modeled net result = quantity × (1 − first entry price − second entry price) − total applicable costs.

Here is a hypothetical 100-pair example:

The $1.20 is an example input, not a current fee quote from any venue. Use the applicable schedules and the cost shown for the actual order. Kalshi's published fee schedule distinguishes standard and non-standard market fees; do not assume a single blanket charge covers every contract.

If you exit before settlement, model the exit prices and costs too. The settlement example does not describe the economics of selling both positions early.

Use the price you can buy

A last trade is historical. A midpoint may be an attractive reference. Neither necessarily tells you what you can buy now.

For an immediate purchase, inspect the available offer and the quantity at that price. If you need more than the displayed quantity, calculate the average entry price across the levels required to fill the order.

For example, assume 20 contracts are available at $0.50 and the next 80 at $0.52. Buying 100 costs $51.60, giving an average price of $0.516. Paired with 100 contracts at $0.47, the gross purchase cost becomes $98.60 rather than $97.

The gross spread is now $1.40. Using the earlier illustrative $1.20 cost input would leave only $0.20. Actual fees would need to be recalculated for the actual fills. A seemingly small depth adjustment can consume most of an opportunity.

Check the smaller side's available size

The matched portion is limited by the quantity you can complete on both sides. If one venue offers 100 contracts and the other offers 25 at the intended price, the immediately visible paired quantity is at most 25.

Do not multiply the headline margin by your entire bankroll. Capital, depth, and opportunity size are separate constraints.

Keep balances in the calculation as well. You need enough available funds at the relevant venues when you place the orders. A balance awaiting transfer or locked in another position is not available for the next pair.

Size also affects your ability to respond if a leg fails. Before entering, decide how much unmatched exposure you could handle and what action you would take. The decision belongs before the first fill, when you still have the option to pass.

Understand the risk between the two legs

The orders are separate. You can fill one side and miss the other because the quote changes, available size disappears, or the venue rejects the order.

At that point you hold a directional position. Its outcome is no longer described by the original paired-return calculation. You may need to accept a worse hedge price, close the first position, or retain exposure. Each choice changes the economics.

A displayed spread cannot remove this risk. Faster clicking does not make two venues atomic, and an alert does not reserve liquidity.

For a manual workflow, establish a maximum entry price, maximum unmatched quantity, and a response to a failed second leg. Keep those rules simple enough to follow under pressure. If the opportunity cannot tolerate your realistic execution delay, passing is a valid result.

A repeatable comparison session

Use the following sequence for each candidate:

1. Find the same event across the relevant venues.
2. Match the exact market, line, period, and settlement rules.
3. Read the current buy prices and depth on both sides.
4. Calculate the result using applicable costs and realistic size.
5. Check balances and decide how to handle an incomplete pair.
6. Place and verify each order at the venues.
7. Record the actual fills and reconcile the final settlement.

The sequence is intentionally repetitive. A shortcut that saves a few seconds can be costly if it skips contract matching or fill verification.

For the arithmetic, use the arbitrage calculator. It accepts prices you provide and excludes real-time discovery and venue-specific fees, so account for those separately. The odds calculator helps compare different price formats.

What TurbineFi Sports contributes

TurbineFi Sports is launching around matched sports-market comparison across Kalshi, Polymarket US, and Novig. It is intended to reduce the work of finding comparable candidates across separate venue screens.

Evaluate it on that contribution: whether the markets you need appear, whether the match is correct, and whether the displayed information helps you make a clear decision. You still place orders at the venues and verify prices, size, rules, and fills.

The launch subscription is $49 monthly, or $294 paid upfront annually, equivalent to $24.50 per month. Check current Sports pricing before subscribing. Do not infer that the subscription guarantees opportunities or makes every displayed candidate actionable.

If you are choosing between a broader betting toolkit and this exchange workflow, read OddsJam alternatives and OddsJam vs Outlier.

What to keep in your trade log

Record the event, venue market identifiers, outcome wording, entry prices, filled quantities, fees, timestamps, and settlement. Include a note when your intended pair differs from the actual position.

Track candidates you reject and why: mismatched rules, insufficient depth, unavailable venue access, or a spread that disappears after costs. That record helps you distinguish a useful discovery process from a screen full of opportunities you cannot use.

Keep gross spread, realized trading result, and subscription cost separate. This makes the accounting easier to inspect and prevents a theoretical margin from being presented as realized profit.

Review operational mistakes as well as outcomes. A winning unmatched position can still reveal a failed process, while a correctly executed strategy can experience adverse costs or other unexpected results.

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View TurbineFi Sports pricing to evaluate the focused three-venue comparison workflow.