How to Trade the 2026 Midterms: Polymarket vs Kalshi

Key takeaways

1. At 21:21 UTC on 8 October 2026, Democrats for the House were 90.5 cents on Polymarket and 90.2 on Kalshi; for the Senate, 63.5 cents against 62.
2. The cheaper venue flips with the side you buy. All in, 100 Democrat-Senate contracts cost $63.65 on Kalshi against $64.92 on Polymarket, while 100 Republican-Senate contracts cost $36.92 on Polymarket against $40.67 on Kalshi.
3. Kalshi's taker fee on these markets is 0.07 x contracts x price x (1 - price) against 0.04 for Polymarket's politics category, so the fee gap is widest on the Senate markets priced near even money.
4. The 2 cent cross-venue gap on Senate control is not free money. Buying both sides across the two exchanges costs 98 cents for a dollar payout, and the two taker fees come to 2.57 cents, so the pair loses about half a cent.
5. The venues resolve the same question differently. Polymarket falls back to the first selected President pro tempore and counts runoffs held after November, while Kalshi may settle early on a consensus of media calls and otherwise reads chamber leadership on 1 February 2027.

On this page

1. What you are actually trading in the 2026 midterms
2. Live prices on both venues, read at one timestamp
3. The fee formula is the part nobody prints
4. All in cost per 100 contracts, and the breakeven it sets
5. The 2 cent gap between venues is not a free trade
6. Polymarket's combo market disagrees with its own single-chamber markets
7. Resolution rules differ, and that is the real risk
8. Sizing a midterm position without donating to the spread
9. Who can legally trade midterm contracts right now
10. Sources and when we last checked
11. Frequently asked questions

This is a plain list rather than a set of jump links, because guide pages on this site render section text as plain paragraphs. Scroll to whichever heading you need.

What you are actually trading in the 2026 midterms

1. House control: all 435 seats are on the ballot and 218 is the majority. The chamber went into the cycle at roughly 218 Republicans to 214 Democrats with a few vacancies, and the published counts differ on exactly how many.
2. Senate control: 35 seats are up, 33 regular Class II seats plus special elections in Ohio and Florida. Republicans hold 22 of the 35 and Democrats hold 13.
3. The majority maths is asymmetric. Democrats need 51 seats and so must win 17 of the 35, while Republicans need only 50 because the Vice President breaks a tie, so 19 is enough.
4. Balance of Power: one multi-outcome market on the four combinations of chamber control plus an 'Other' leg, and the deepest pool of midterm money on either venue.

Election day is Tuesday 3 November 2026, and the markets worth your attention come in three shapes rather than one. There are two single-chamber control markets, a combination market that prices both chambers at once, and a long tail of individual races, turnout bands and popular-vote margin buckets.

The shape you pick decides your cost before you have formed any opinion. A single-chamber market is one leg and one fee. The combination market gives you a correlated pair inside one contract, cheaper than legging it yourself but much thinner at the extremes. The margin and turnout markets are thin enough that the spread, not the fee, beats you.

Live prices on both venues, read at one timestamp

1. Democrats win the House: Polymarket 90.5 cents (bid 90, ask 91), Kalshi 90.2 cents (bid 90.10, ask 90.20)
2. Republicans win the House: Polymarket 9.5 cents (bid 9, ask 10), Kalshi 10 cents (bid 9.90, ask 10.00)
3. Democrats win the Senate: Polymarket 63.5 cents (bid 63, ask 64), Kalshi 62 cents (bid 61, ask 62)
4. Republicans win the Senate: Polymarket 35.5 cents (bid 35, ask 36), Kalshi 39 cents (bid 38, ask 39)
5. Balance of Power on Polymarket: Democrats sweep 63.5, Republicans take the Senate while Democrats take the House 27.5, Republicans sweep 8.5, Democrats take the Senate while Republicans take the House 0.75, Other 0.25

Every figure above was read at 21:21 UTC on 8 October 2026, Polymarket's from its public Gamma API and Kalshi's from its public market endpoint. One timestamp matters more than it sounds: the trackers that dominate this search average several sources on different clocks, and one of the biggest currently shows Democrats at 63% for the Senate in its table while the prose beside it says Republicans are 57% to win the chamber.

The story is agreement on the House and disagreement on the Senate. Both venues have the House a touch over 90 cents for Democrats, which is as close to consensus as prediction markets get. The Senate is 1.5 to 3 points apart depending on which side you look at, and that gap is the only genuinely tradeable thing on this page.

One trap while you compare. Polymarket reports volume in dollars and Kalshi reports it in contracts, so setting the two headline numbers side by side, as several trackers do, compares a dollar figure to a count. Kalshi's Republicans-win-the-House contract showed about 32.3 million contracts traded and 22.9 million of open interest, which is a large position count on a market trading near a dime, not $32 million of risk. Compare spreads and resting size instead: all four control markets were quoting one cent wide.

The fee formula is the part nobody prints

1. Polymarket global, politics category: fee = 0.04 x contracts x price x (1 - price). Makers are never charged and can earn a 25% rebate from collected taker fees in this category.
2. Polymarket US, effective 10am ET on 1 October 2026: taker coefficient 0.0695, maker rebate coefficient 0.0125 paid to you, peaking at $1.74 per 100 contracts at a 50 cent price.
3. Polymarket US volume rebates on prior calendar-month taker volume: 10% from $250,000, 25% from $1,000,000, 50% from $10,000,000.
4. Kalshi takers: fee = 0.07 x contracts x price x (1 - price), rounded up to the next cent.
5. Kalshi makers: treatment varies by series and the public write-ups disagree, so read the schedule for the ticker you are about to trade.

Both venues charge on the same curve at different rates, and the curve comes first. Multiplying by price x (1 - price) makes a parabola that peaks at 50 cents and falls to almost nothing at both ends, so the fee is largest exactly where the market is least certain. That is why the midterm Senate markets are the expensive ones and the House markets are nearly free.

Put the published rates against the live prices and the gap is concrete. On Democrats to win the Senate at 62 to 64 cents, Kalshi's coefficient costs $1.65 per 100 contracts while Polymarket's politics rate costs 92 cents. On Democrats to win the House near 90 cents it is 62 cents against 33 cents. Kalshi works out about 1.8 times dearer on the Senate leg and about 1.9 times dearer on the House leg, a shade above the 1.75 the two coefficients alone imply, because Kalshi rounds every fee up to the next whole cent.

If you trade the regulated Polymarket US venue you are on the 0.0695 schedule that took effect on 1 October 2026, where posting a resting order earns you 0.0125 rather than costing anything. Makers are treated well on both platforms, which is the cheapest single change most readers of this page could make.

All in cost per 100 contracts, and the breakeven it sets

1. Democrats win the House: Polymarket $91.33 all in, Kalshi $90.82. Kalshi cheaper by 51 cents. Breakeven 91.33% against 90.82%.
2. Republicans win the House: Polymarket $10.36 all in, Kalshi $10.63. Polymarket cheaper by 27 cents. Breakeven 10.36% against 10.63%.
3. Democrats win the Senate: Polymarket $64.92 all in, Kalshi $63.65. Kalshi cheaper by $1.27. Breakeven 64.92% against 63.65%.
4. Republicans win the Senate: Polymarket $36.92 all in, Kalshi $40.67. Polymarket cheaper by $3.75. Breakeven 36.92% against 40.67%.

This is the table the guides owe you and never build. Take the price you can actually buy at, which is the ask rather than the midpoint, add the taker fee the venue's own formula produces, and you have the real cost of the position and therefore the probability you have to beat.

No venue wins outright. Kalshi is cheaper for both Democratic legs and Polymarket for both Republican legs, and the reason is price rather than fees. Kalshi's higher coefficient costs 73 cents more per 100 on the Senate, but its Democratic side is quoted 2 cents lower, which is worth $2.00. Where the two agree on price, as they nearly do on the House, the fee decides and Kalshi's slightly lower ask still edges it.

So the honest conclusion is the inconvenient one: you cannot pick a home venue for the midterms and be done. The Republican Senate leg costs 10% more of your stake on the wrong exchange, $40.67 against $36.92 for the same dollar of payout. Check both asks on the specific leg you want, and treat any guide that names one winner as not having looked.

The 2 cent gap between venues is not a free trade

1. Buy Democrats for Senate on Kalshi at the 62 cent ask, buy Republicans for Senate on Polymarket at the 36 cent ask: 98 cents outlay for a position that pays exactly $1.00
2. Gross edge: 2.00 cents per pair
3. Kalshi taker fee at 62 cents: 1.65 cents per contract
4. Polymarket politics fee at 36 cents: 0.92 cents per contract
5. Net result: minus 0.57 cents per pair, before a cent of spread or deposit cost

Here is where a cross-venue price comparison usually stops and where it should start. A 2 cent gap on a dollar payout looks like the textbook arbitrage, and on a fee-free exchange it would be. Both of these exchanges charge takers, and the two fees together are larger than the gap.

The reverse pair is worse, which is a useful check that you have the right legs. Buying the Democratic side on Polymarket at 64 cents and the Republican side on Kalshi at 39 cents costs $1.03 for the same dollar. Note too that Kalshi's own two sides summed to $1.01 while Polymarket's summed to exactly $1.00, so the Kalshi book itself carried a one cent overround.

The lesson generalises past the midterms. A cross-venue gap has to clear the sum of both taker fees before it is worth anything, which near 50 cents means roughly 2.5 cents on this pairing. Gaps that size do appear, usually for minutes after a news shock, and they are taken by people already funded on both venues and posting as makers rather than crossing two spreads.

Polymarket's combo market disagrees with its own single-chamber markets

1. Balance of Power legs sum to 100.5 cents, a half cent overround on the combination market
2. Implied Democratic House from the combos: 63.5 plus 27.5 equals 91.0 cents, against 90.5 cents on the standalone House market
3. Implied Democratic Senate from the combos: 63.5 plus 0.75 equals 64.25 cents, against 63.5 cents on the standalone Senate market
4. Both gaps point the same way: the combination market prices Democrats slightly higher in both chambers

You can check this one yourself in a minute and almost nobody does. Polymarket runs Balance of Power and the two single-chamber markets side by side, and the combinations imply chamber probabilities that should match the standalone contracts. At our snapshot they did not, by half a point on the House and three quarters of a point on the Senate.

That is a real inefficiency and also too small to trade, which is the part worth internalising. Capturing the Senate discrepancy means two legs and therefore two taker fees. At 92 cents per 100 contracts per leg on the politics rate you would pay about 1.8 cents per pair to collect three quarters of a cent. The gap has to roughly treble before the trade is even flat.

What it is good for is reading the market properly. When the combination market and the single-chamber markets disagree, the deeper book is usually the better number, and on the midterms that is Balance of Power with $20.4 million traded against $6 million on the Senate. If you want one figure for Democratic Senate control, 64.25 cents from the deeper market is a defensible answer, and so is treating the half point of disagreement as the honest width of the estimate.

Resolution rules differ, and that is the real risk

1. Polymarket: control goes to the party winning a majority of voting seats. On a 50-50 Senate it goes to the party holding the Vice Presidency. If still ambiguous it goes to the party of the first selected President pro tempore of the Congress that convenes after the election.
2. Polymarket counts all regular and special Senate elections scheduled for November 2026 as of 31 October 2026, and runoffs decide their seat even when they fall after November.
3. Kalshi: the market may be determined early on a consensus of media calls projecting control.
4. Otherwise Kalshi reads the party identification of the Speaker of the House, or of the President pro tempore of the Senate, on 1 February 2027. Its control markets carry a close time of 1 February 2027.

This is the section the trackers skip and the one that can cost you your stake rather than a fee. You are not trading 'who wins the Senate'. You are trading one contract's definition of it, and the two biggest venues wrote that definition differently.

The practical differences are timing and tiebreak. Kalshi can settle within the hour once the networks reach a consensus call, which is why its contracts often pay out on election night despite a February close. Polymarket lists 4 November 2026, but its own rules count runoffs held later, so a Georgia-style second round in a decisive seat leaves the question open past the date on screen. Read 'end date' as scheduled, not guaranteed.

The tiebreak is where the two could in principle disagree on the same outcome. Both fall back to chamber leadership, but Kalshi takes a snapshot on a fixed day while Polymarket takes the first selection by the incoming Congress. Ordinarily these agree. In a contested, delayed or litigated chamber, exactly the scenario that makes a 63 cent contract interesting, they need not. Kalshi also settles as the exchange on its own rules, while Polymarket's global markets settle through an oracle with a dispute window: different failure modes, and worth knowing which one you hold.

Sizing a midterm position without donating to the spread

1. Democrats for the House on Kalshi, all in at $90.82 per 100: profit $9.18, a 10.1% return on the money at risk
2. Democrats for the Senate on Kalshi, all in at $63.65 per 100: profit $36.35, a 57.1% return
3. Republicans for the Senate on Polymarket, all in at $36.92 per 100: profit $63.08, a 170.9% return
4. Spread cost on the thin markets: the House turnout bands were quoting up to 13.5 cents wide and the popular-vote margin buckets up to 2.7 cents, against 1 cent on all four control markets

Those three returns are the same bet at three prices, and the first is the one people get wrong. A 90 cent favourite returns about a tenth of your stake and risks all of it, so it has to be right better than nine times in ten to earn anything. That is not an argument against favourites, but against buying them in size you would not accept losing.

The bigger drag is the spread, not the fee. The four control markets were a cent wide, so crossing costs half a cent of edge. The 130 million and above turnout leg was quoted 5.5 bid at 19 offered: a 13.5 cent spread on a contract marked near 12 cents. A spread an order of magnitude wider than the fee is not a market you can trade actively, whatever the schedule says. Cost first, opinion second: if your read on the Senate is 65% and the all in cost is 64.92%, you do not have a trade, you have a rounding error.

Who can legally trade midterm contracts right now

Both venues hold CFTC designated contract market status, which is what lets them list election event contracts at all. The federal position firmed up after a court held in late 2024 that election contracts were not illegal gambling under the Commodity Exchange Act and the CFTC withdrew its challenge. Polymarket returned to the United States by acquiring a CFTC-licensed exchange and clearinghouse rather than by winning a licence from scratch.

Access is decided by where you physically are when you trade, not where you live, and it is confirmed by a geo-check in the app. State-level friction is the live risk rather than federal law: a court order in Nevada led to election, sports and entertainment contracts being withdrawn from users in that state, and the broader appellate fight now moving through the federal courts is mainly about sports contracts rather than elections. Our state-by-state directory and our guide to where Polymarket is legal track it in more detail, and the geo-check on the venue you want is the definitive answer for your own situation.

One more thing worth knowing before November: the two venues run separate order books, and so do the global and US Polymarket platforms, so the regulated US app can print a different price from the figures above. Check the book you are actually trading.

Sources and when we last checked

1. Polymarket Gamma API, gamma-api.polymarket.com, read 21:21 UTC on 8 October 2026: all Polymarket prices, volumes, resting liquidity and the resolution text quoted above
2. Kalshi public market API, api.elections.kalshi.com, read 21:21 UTC on 8 October 2026: the CONTROLH-2026 and CONTROLS-2026 bids, asks, volumes, open interest and rules
3. Polymarket US fee schedule, docs.polymarket.us/fees: the 0.0695 taker coefficient, the 0.0125 maker rebate and the volume rebate tiers effective 10am ET on 1 October 2026
4. Polymarket global trading fees, help.polymarket.com article 13364478: the fee formula and the 0.04 politics category rate
5. Kalshi's published fee schedule and help centre: the 0.07 taker coefficient and the round-up-to-the-cent rule
6. Ballotpedia and the Bipartisan Policy Center for the 3 November 2026 date, the 35 Senate seats and the chamber arithmetic

Every price here is one timestamp and will be stale by the time you read it, which is why the formulas matter more than the numbers. Fee schedules moved more than once during 2026 and the Polymarket US one changed as recently as 1 October, so confirm the rate for your venue and category before sizing anything real. Where sources disagreed, which they do on Kalshi's maker treatment and the exact House vacancy count, we say so rather than pick one.

Frequently asked questions

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