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Updated September 25, 2026 · facts checked against the dated sources listed below
Comparing the two exchanges takes four steps: find the same question, check that both pay out on the same facts, add each side's fee to the price you would actually pay, and only then read the gap. On September 25, 2026 most outcomes priced on both were within 2 points of each other, and the bigger gaps usually had a reason.
Start on one exchange and find the twin on the other. Polymarket's Fed Decision in December? and Kalshi's Fed decision in Dec 2026? both price the Federal Reserve's decision of December 9, 2026 in five buckets. The labels differ, so line them up by meaning: Polymarket's 25 bps increase is Kalshi's Hike 25bps, No change is Fed maintains rate, and 50+ bps increase is Kalshi's bucket for a hike of more than 25bps.
At about 10:30 UTC on September 25, 2026, the 25 bp hike had a Polymarket bid of 71¢ and ask of 72¢, a 71.5% midpoint, and a Kalshi bid of 70¢ and ask of 71¢, a 70.5% midpoint: a 1-point gap. This site lines up events like this one side by side and refreshes them twice a day, and our sister site Kalshi View shows the same comparison from the Kalshi side.
See also: Polymarket vs Kalshi odds today · Fed December on both exchanges · Kalshi vs Polymarket odds on Kalshi View
Both Fed markets settle on the Fed's own decision, but the fine print differs. Polymarket measures the change in the upper bound of the target range, rounds a move that is not listed up to the nearest 25 basis points, and resolves to No change if no statement is released by the end date of the next scheduled meeting. Kalshi's buckets are mutually exclusive, and if the scheduled meeting is canceled, Fed maintains rate resolves Yes. Kalshi stops trading at 1:59 p.m. Eastern on December 9; Polymarket lists 11:59 p.m. that day as its end date and may resolve as soon as the Fed's statement is out.
Rules can differ by more than timing. Polymarket's US recession by end of 2026? pays Yes on two straight quarters of negative real GDP growth or on an NBER recession announcement; Kalshi's Recession this year? counts only the two negative quarters reported by the Bureau of Economic Analysis. At the same time on September 25, Polymarket's midpoint was 9.5% and Kalshi's 5.5%. Part of that 4-point gap can come from the wider Polymarket rule, since an NBER call alone would pay Polymarket's Yes holders but not Kalshi's.
See also: US recession on both exchanges · How Polymarket markets resolve
Polymarket charges takers shares × fee rate × price × (1 − price), with a rate of 0.05 on economics markets, rounds fees to five decimal places and never charges makers. Kalshi's fee schedule, in the version effective February 5, 2026, charges takers 0.07 × contracts × price × (1 − price), rounded up to the next cent. Some markets also carry a smaller maker fee, which Kalshi's help center says is charged only when a resting order is filled, never for canceling; Kalshi's API lists the Fed decision series with maker fees and a fee multiplier of 1. Both formulas peak at 50¢, and Kalshi points traders to its fee schedule page for current changes.
Take 100 contracts on a 25 bp December hike at those quotes. On Polymarket, the 72¢ ask plus 100 × 0.05 × 0.72 × 0.28 = $1.008 in fees comes to $73.01. On Kalshi, under that schedule, the 71¢ ask plus 0.07 × 100 × 0.71 × 0.29 = $1.4413, rounded up to $1.45, comes to $72.45, so Kalshi was 56 cents cheaper for Yes. For No the order flips: Polymarket's 29¢ No plus $1.03 in fees costs $30.03, while Kalshi's 30¢ No plus $1.47 costs $31.47.
See also: Polymarket fee calculator
A gap is worth noticing only after fees and rules. This site's price-gap study compares every outcome priced on both exchanges; on September 25, 2026 it covered 216 outcomes, with a median gap of 1 point; all but 3 were within 5 points, and the widest gap was 8 points.
Buying Yes on one exchange and No on the other locks in a profit only if the two costs, fees included, add up to less than the $1 payout and both contracts settle on the same facts. In the Fed example, Kalshi's Yes at 72.45¢ all-in plus Polymarket's No at 30.03¢ came to about $1.02 a pair, so the 1-point gap was not free money.
See also: Polymarket and Kalshi price gaps · Polymarket arbitrage calculator
The two exchanges have different traders and different doors. Polymarket.com is not open to US residents, who use a separate Polymarket US app with its own accounts, while Kalshi is a US exchange regulated by the CFTC as a designated contract market. Money does not move instantly between them, both charge fees, and capital sits idle until settlement: Kalshi says determination can take from one hour to more than twelve hours after a market closes, and a disputed Polymarket resolution takes four to six days.
Different wording explains the rest. When the rules differ, as in the recession pair, a gap can be a fair price for a different question rather than a mistake to trade.
See also: Polymarket US · Polymarket vs Kalshi compared
Close, but rarely identical. Across 216 outcomes priced on both exchanges on September 25, 2026, the median gap was 1 point and all but 3 were within 5 points.
It depends on the market, the side and the moment. In the December Fed example, Kalshi was cheaper for Yes and Polymarket for No once each exchange's ask and taker fee were added.
Only if Yes on one side plus No on the other costs less than $1 after fees and both contracts settle on the same facts. Access rules, transfer times and money tied up until settlement get in the way too.
On this site's Polymarket vs Kalshi pages, refreshed twice a day, and on our sister site Kalshi View.
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