What it really costs to trade: bid-ask spreads across 438,000 open Kalshi and Polymarket markets
We pulled every open market on Kalshi and Polymarket and measured the gap between the best bid and ask. Most markets do not trade on a given day; among those that do, the median spread was 2¢ on Kalshi and 2.4¢ on Polymarket, falling to 1¢ in the busiest markets. Spreads by volume, price and category, and how to keep trading costs down.
In this article
The price you see is not the price you pay. Every prediction market has two prices: the best bid, what someone will pay you, and the best ask, what you must pay. The gap between them, the spread, is a cost every trader pays on top of fees. We measured it across every open market on Kalshi and Polymarket on 30 October 2026: 169,248 markets on Kalshi and 268,947 on Polymarket's international site.
The headline: most markets barely trade, and those that do are cheap to trade only when they are busy. Among markets that traded in the previous 24 hours, the median spread was 2¢ on Kalshi and 2.4¢ on Polymarket. In the busiest markets it fell to 1¢, the minimum on most contracts.
Key findings
Source: Our analysis of the Kalshi and Polymarket public APIs, 30 October 2026
- Only 14.6% of open Kalshi markets and 8.3% of open Polymarket markets traded at all in the previous 24 hours.
- Among markets that traded, the median spread was 2¢ on Kalshi and 2.4¢ on Polymarket; the average was much higher, 6.1¢ and 7.7¢, because of a long tail of wide markets.
- About 28% of active markets on each platform had spreads wider than 5¢.
- In markets trading more than 100,000 contracts (Kalshi) or $100,000 (Polymarket) a day, 93% and 90% had a 1¢ spread.
- Spreads were tightest for long shots under 10¢ and for near-certainties over 90¢, and widest in between.
How we did it
| Kalshi | Polymarket | |
|---|---|---|
| What we pulled | Every open market (excluding combination markets) | Every open market accepting orders on polymarket.com |
| When | 30 October 2026, 15:46 UTC | 30 October 2026, 15:38–15:44 UTC |
| Open markets | 169,248 | 268,947 |
| With a two-sided quote | 107,240 (63.4%) | 146,027 (54.3%) |
| Traded in the last 24 hours | 24,781 (14.6%) | 22,196 (8.3%) |
| Traded and two-sided (main sample) | 21,761 | 19,957 |
| Volume unit | Contracts (each pays $1) | US dollars |
We excluded Kalshi's combination markets, the parlay-style contracts that bundle several outcomes. There are at least 399,000 of them, and almost none have quotes. We counted a market as two-sided if it had a bid above zero and an ask below $1. The spread is the ask minus the bid. Polymarket here is the international site; Polymarket US has its own books.
The summary tables are in the open data file.
Most markets are quiet
Both exchanges list far more markets than people trade. On Kalshi, a single football game can carry dozens of markets on the winner, the spread, total points and individual players; a tennis tournament lists every match. On Polymarket, most open markets are sports props and match markets. On a typical day the great majority sit untouched.
That matters because quotes in quiet markets are often wide or stale. Across all two-sided markets, including the ones nobody traded, the median spread was 7¢ on Kalshi and 21¢ on Polymarket. If you trade a market nobody else is trading, expect to pay for it.
Busier markets are cheaper
Source: Our analysis, 30 October 2026
Show the dataHide the data
| Kalshi | Polymarket | |
|---|---|---|
| 1–99 | 3¢ | 3¢ |
| 100–999 | 2¢ | 2.7¢ |
| 1k–10k | 1¢ | 1.2¢ |
| 10k–100k | 1¢ | 1¢ |
| 100k+ | 1¢ | 1¢ |
The pattern is the same on both platforms. Markets trading under 100 contracts or dollars a day had a median spread of 3¢. Above 1,000 a day it fell to about 1¢. The share of markets quoted at the minimum spread rose steadily with activity:
Source: Our analysis, 30 October 2026
Show the dataHide the data
| Kalshi | Polymarket | |
|---|---|---|
| 1–99 | 26.4% | 24.5% |
| 100–999 | 38.4% | 29% |
| 1k–10k | 60.7% | 48.7% |
| 10k–100k | 86.7% | 74.4% |
| 100k+ | 93.1% | 89.8% |
At each level of activity, Kalshi was somewhat more likely to be quoted at 1¢. Keep in mind that the units differ: a Kalshi contract has a face value of $1, while Polymarket volume is in dollars traded, so the buckets are close but not identical.
| 24-hour volume | Kalshi markets | Kalshi median | Polymarket markets | Polymarket median |
|---|---|---|---|---|
| 1–99 | 10,260 | 3.0¢ | 9,851 | 3.0¢ |
| 100–999 | 6,772 | 2.0¢ | 7,010 | 2.7¢ |
| 1,000–9,999 | 2,897 | 1.0¢ | 2,316 | 1.2¢ |
| 10,000–99,999 | 878 | 1.0¢ | 617 | 1.0¢ |
| 100,000 and over | 160 | 1.0¢ | 88 | 1.0¢ |
Spreads by price
Source: Our analysis, 30 October 2026
Show the dataHide the data
| Kalshi | Polymarket | |
|---|---|---|
| 0–10¢ | 1¢ | 1.7¢ |
| 10–30¢ | 3¢ | 3¢ |
| 30–70¢ | 3¢ | 3¢ |
| 70–90¢ | 4¢ | 3¢ |
| 90–100¢ | 1.3¢ | 2¢ |
Spreads in cents were tightest at the extremes, for long shots under 10¢ and near-certainties over 90¢, and about 3¢ in between. In relative terms the picture flips: a 1¢ spread on a 5¢ long shot is 20% of the price, while a 3¢ spread on a 50¢ contract is 6%. Cheap contracts look cheap to trade, but proportionally they are the most expensive.
Spreads by category
| Category | Kalshi median spread | Polymarket median spread |
|---|---|---|
| Sports | 2.0¢ | 2.0¢ |
| Politics and elections | 3.0¢ | 3.0¢ |
| Crypto | 2.0¢ | 3.0¢ |
| Economy and finance | 4.0¢ | 4.0¢ |
| Culture | 4.0¢ | 2.5¢ |
| Weather | 3.0¢ | 2.0¢ |
| Tech and AI | 4.0¢ | 3.0¢ |
| Geopolitics | — | 2.6¢ |
Markets that traded in the last 24 hours. Categories are each platform's own, grouped by us; Kalshi has almost no geopolitics markets.
Sports were the cheapest category to trade on both platforms, helped by the sheer number of active game markets. Economy and finance markets, many of them price ladders on indices, rates and commodities, were the most expensive at 4¢. Our study of what people bet on shows where the volume is.
What a spread costs you
If you buy at the ask and later sell at the bid, the spread is what you lose even if the price never moves. Some examples, before fees:
| Contract price | Spread | Round-trip cost as share of stake |
|---|---|---|
| 50¢ | 1¢ | 2% |
| 50¢ | 3¢ | 6% |
| 20¢ | 2¢ | 10% |
| 5¢ | 1¢ | 20% |
Fees come on top. Kalshi charges takers 0.07 × price × (1 − price) per contract, with the total rounded up to the next cent, so about 2¢ on a single 50¢ contract. Polymarket US charges 0.0695 × price × (1 − price), and Polymarket's international site charges takers by category (Polymarket fees; Kalshi fees). If you hold to settlement you pay the spread only once, on entry.
A worked example
Say you buy 100 "Yes" contracts on Kalshi at an ask of 52¢, in a market where the best bid is 50¢:
| Step | Cost |
|---|---|
| Buy 100 contracts at 52¢ | $52.00 |
| Kalshi taker fee: 0.07 × 100 × 0.52 × 0.48 = $1.7472, rounded up | $1.75 |
| Value if you sold straight back at the 50¢ bid | $50.00 |
| Taker fee on the sale at 50¢: 0.07 × 100 × 0.50 × 0.50 | $1.75 |
| Round-trip cost if the price does not move | $5.50, about 10.6% of $52 |
About a third of that is the spread and two-thirds the fees. If you hold to settlement there is no exit trade and no second fee, which is why holding is cheaper than trading in and out. If you place a limit bid at 51¢ and someone sells to you, you save a cent a contract and may pay a lower maker fee. That is why active traders rarely cross the spread in quiet markets.
Why some markets have wide spreads
Spreads are set by whoever is quoting. On both exchanges, professional market makers provide much of the liquidity in popular markets, and they widen their quotes when:
- Few people trade the market, so it takes longer to unwind a position.
- News could arrive at any moment, such as during a live game or on election night.
- The outcome is hard to price, as in long-dated or novel markets.
- Someone may know more than they do. Market makers lose money to better-informed traders, and they price that risk into the spread.
Busy markets with steady two-way flow give them less risk per trade, which is why spreads there shrink to the 1¢ minimum. Quiet markets get the opposite treatment, and a wide quote is often simply the only quote.
The same market on both exchanges
Our price comparison study, taken minutes after this snapshot, looked at 91 liquid outcomes listed on both Kalshi and Polymarket. Both exchanges had a median spread of 1¢ in those markets; Kalshi's quote was tighter in 33 cases and Polymarket's in 22. For popular events, the difference in trading costs between the two is small. For niche markets, it can be large in either direction.
How to keep trading costs down
- Trade busy markets. Spreads fall to 1¢ once a market trades a few thousand contracts a day.
- Use limit orders. Placing a bid inside the spread and waiting often saves a cent or two, and makers usually pay lower fees than takers (limit vs market orders).
- Compare exchanges. The same outcome can be cheaper on the other platform (our price comparison).
- Be careful with long shots. A 1¢ spread on a 4¢ contract is a quarter of the price.
- Hold when it makes sense. Every round trip pays the spread; holding to settlement pays it once.
- Watch for slippage. Big orders eat through several price levels; our guide to slippage, volume and spreads explains how.
Limitations
This is one snapshot, taken on a Friday afternoon (UTC) five days before the midterms. Spreads change by the second and vary through the day. We measured the best bid and ask only, not the depth behind them, which matters for large orders. Kalshi volume is counted in contracts and Polymarket volume in dollars. Polymarket US, which has its own order books, is not included.
Data
Related reading
- Kalshi slippage, volume and spreads explained
- Limit order vs market order
- Kalshi vs Polymarket prices: 351 outcomes compared
- What do people bet on? Volume by category
- Polymarket fees vs Kalshi fees
This study uses public market data and is not investment advice.
