All terms A to Z
A API key scopes, Arbitrage, Ask. B Bid, Binary contract, Break-even probability. C CFTC, Clearinghouse, Client order ID, Close time, Collateral return, Combo. D Designated contract market, Depth, Determination, Dispute. E Edge, Event, Event contract, Expected expiration time, Expected value. F Fair price, Favorite-longshot bias, FCM, Fee multiplier, Fill, Fill or kill, Fractional contract, Fractional Kelly, Fully collateralized. G Good till canceled. H Hedge. I Immediate or cancel, Implied probability. K Kelly fraction. L Last price, Last traded price settlement, Latest expiration time, Limit order, Liquidity, Liquidity incentive program. M Maker, Market, Market maker, Market order, Midpoint, Mutually exclusive event. O Open interest, Order book, Order group, Overround. P Post-only. Q Queue position. R Reduce-only, RFQ, Rounding fee, Rulebook, Rules. S Scalar contract, Self-trade prevention, Series, Settlement, Settlement timer, Source agency, Spread, Strike, Subaccount. T Taker, Ticker, Tick size. V Volume. Y YES and NO.
Contracts and markets
Kalshi nests its products three levels deep. This example comes from Kalshi's API documentation.
| Level | Example ticker | What it is |
|---|---|---|
| Series | KXAAAGASM | US gas price, asked every month |
| Event | KXAAAGASM-26SEP30 | The gas price on Sep 30, 2026 |
| Market | KXAAAGASM-26SEP30-3.00 | One strike in that event, "Above 3.00" |
Event contract
A contract whose payoff depends on whether something happens, such as a data release, a game or an election. The CFTC says event contracts are often yes-or-no questions with a fixed payout, usually $1, and a set expiration.
Binary contract
A contract with two outcomes, YES or NO. On Kalshi the winning side receives $1 per contract at settlement and the losing side receives nothing. Most Kalshi markets are binary.
Scalar contract
A contract that can pay both sides part of the $1. Kalshi's NFL ladder markets work this way. Take a ladder that pays 5c per catch, up to $1 at 20 catches. On 6 catches it pays YES 30c and NO 70c.
YES and NO
The two sides of every market. A trade pairs a YES buyer and a NO buyer whose prices add up to $1, such as 70c against 30c. Buying NO at 30c and selling YES at 70c are the same trade on Kalshi.
Series
A question Kalshi lists again and again over separate periods, such as a monthly gas price. Its events measure the same kind of data and share a ticker prefix. Kalshi sets fees per series.
Event
One instance of a series, such as the gas price on Sep 30, 2026. It holds one or more markets. Kalshi's documentation calls the event the basic unit traders interact with.
Market
One tradable outcome inside an event, with its own order book, price and rules. In an election event each candidate is a market, as in how Kalshi election markets settle. In a numeric event each strike is a market.
Strike
The threshold a numeric market is written around, such as "Above 3.00". The API field strike_type says how it is tested. Strikes in one event settle on the same number, so a higher "above" threshold can never be likelier than a lower one.
Ticker
The exchange's ID for a series, event or market, as in KXHIGHNY, KXHIGHNY-24JAN01 and KXHIGHNY-24JAN01-T60. Kalshi warns of exceptions to that pattern and tells developers to read series_ticker and event_ticker instead of parsing the string.
Mutually exclusive event
An event in which at most one market can settle YES, such as a list of candidates for one office. The API sets mutually_exclusive to true. Fair YES prices in such an event add up to $1 or less.
Collateral return
An opt-in setting that frees cash when your positions in one event cannot all lose. Say you hold NO at 60c and NO at 70c on two candidates for one office. They cost $1.30, but one must pay $1, so Kalshi holds only the 30c at risk.
Combo
One contract built from positions in several events. It has its own order book, and its prices are set through RFQs. It pays the product of its legs. One leg at $0 makes it worth $0. One leg at a 70c fair price, with the rest at $1, pays 70c.
Prices and the order book
Implied probability
The price in cents divided by 100. A YES contract at 63c implies 63%. The ask, bid, midpoint and last trade can each imply a different number. See Kalshi odds explained and the Kalshi odds converter.
Bid
The highest price anyone will pay right now. It is what you receive if you sell into it. Kalshi's API returns only bids, for YES and for NO, because a YES bid at 60c is the same order as a NO ask at 40c.
Ask
The lowest price anyone will sell at right now. It is what you pay to buy now. The best YES ask equals $1 minus the best NO bid, so a NO bid at 45c shows up as a YES ask at 55c.
Spread
The gap between the best ask and the best bid. A 52c bid against a 55c ask is a 3c spread. Buying and selling straight back costs the spread plus a fee on each trade.
Midpoint
The average of the best bid and ask. A 52c bid and a 55c ask give a 53.5c midpoint. When the spread is narrow, the midpoint is a common summary of the market's view.
Last price
The price of the most recent YES trade. In a quiet market it can be hours old and sit outside the current bid and ask.
Order book
The resting orders in a market, with the contracts waiting at each price. Kalshi's API lists the book as YES bids and NO bids. How to read the Kalshi order book walks through one.
Depth
The contracts resting at each price near the top of the book. In Kalshi's own example, 500 YES contracts at 10c with more at 12c mean a 1,000-contract buy averages 11c.
Liquidity
How easily you can trade real size near the current price. A liquid market has a tight spread and depth on both sides. A market with heavy volume can still be thin when you want to trade.
Queue position
The contracts resting ahead of your order at the same price, which fill first. Kalshi's API reports it for each resting order.
Tick size
The smallest price step a market accepts. The standard step is 1c. Markets with subpenny pricing use finer steps in some bands, such as 0.1c below 10c and above 90c. The API lists each market's grid in price_ranges.
Fractional contract
A position smaller than one contract. Since Apr 17, 2026 every Kalshi market supports fractional trading, down to 0.01 contracts. The API sends counts and prices as strings, such as "10.00" contracts at "0.4200" dollars.
Volume
The contracts traded over a market's life or over a window such as 24 hours. It shows how much interest a market has drawn. It says little about what you can buy at the current price.
Open interest
The contracts still outstanding, bought and not yet closed or settled. Each has a YES holder and a NO holder and counts once. It rises when two traders open new positions against each other and falls as positions close.
Overround
How far the YES asks in a mutually exclusive event add up past $1. Asks of 48c, 30c, 18c and 10c sum to $1.06, a 6c overround. Dividing each price by $1.06 is the simplest way to remove it.
Orders
Limit order
An order to buy or sell at a set price or better. Whatever cannot fill at once rests on the book until it fills, expires or is canceled. Canceling is free. See Kalshi limit orders.
Market order
An order to trade at once at the best available prices, walking the book if the first level runs out. Kalshi's app calls it a quick order. The API dropped the market type on Feb 11, 2026, so API traders price a limit order to cross the spread.
Good till canceled
A time-in-force setting. The order rests until it fills, you cancel it or an expiration time you set passes. Kalshi's API also accepts immediate or cancel and fill or kill. Kalshi cancels all resting orders shortly after a market closes.
Immediate or cancel
An order that fills what it can at once and cancels the rest. It never rests on the book.
Fill or kill
An order that fills in full at once or not at all. If the book cannot supply the whole size at your price, nothing trades.
Post-only
A flag that keeps an order from crossing the spread and filling at once, so it can only rest. When it fills, it fills as a maker, which costs nothing on most series.
Reduce-only
A flag that caps an order at the size of your position, so it can shrink the position but never open or flip one. Kalshi's API accepts it only on immediate-or-cancel orders.
Self-trade prevention
A setting that stops your own orders from trading with each other, across all your subaccounts. Kalshi's V2 order endpoint requires it on every order. With taker_at_cross Kalshi cancels the incoming order. With maker it cancels the resting order and the new one keeps matching.
Client order ID
A unique ID you attach to an order before sending it. Kalshi uses it to catch duplicates. If a response is lost and you resend with the same ID, Kalshi rejects the copy as an order that already exists. So a retry cannot place a second order.
Fill
The part of an order that has traded. An order for 100 contracts can fill 40 at once and rest for the other 60, which leaves it partly filled.
Order group
Orders that share a contract limit. If fills in the group pass the limit within a rolling 15 seconds, Kalshi cancels the group's resting orders and blocks new ones until you reset it. It works as a circuit breaker for quoting.
RFQ
Request for quote. You ask for a price on a set size, and makers reply privately. You accept one, and that maker confirms. Makers get 30 seconds to confirm, or 3 seconds on combos and other high-volatility markets.
Market maker
A trader who keeps orders on both sides of a market and aims to earn the spread. Kalshi's rulebook also names designated Market Makers, who get certain privileges for meeting set requirements.
Fees
Kalshi's fee schedule sets one formula for takers and one for makers. C is the number of contracts, P is the price in dollars and M is the series fee multiplier, which is 1 on most series. The maker formula applies only on series that charge makers.
Kalshi fees explained has the full table, and the Kalshi fee calculator runs the formula for any order.
Taker
The side whose order filled at once against an order already on the book. Takers pay the trading fee. At a multiplier of 1, 100 contracts pay $1.75 at 50c and $0.63 at 10c.
Maker
The side whose order was resting when it filled. Makers pay nothing on most series. Series whose API fee_type includes maker fees charge makers 0.0175 in place of 0.07, a quarter of the taker rate. Since Aug 20, 2026, combo series charge makers half the taker rate, except combos whose legs all come from different NFL games.
Fee multiplier
The M in the fee formula, set per series and returned by the API as fee_multiplier. Most series use 1. A few use 0.5, which halves the fee, and a few use 0, which makes them fee-free. The fee_type field says whether makers pay too. Kalshi can also override the fee for a single event.
Rounding fee
A small charge that keeps balances on Kalshi's precision grid: $0.0001 for direct members and $0.01 for others. The trade fee itself rounds up to $0.000001. Overpayment across an order's fills comes back as a rebate.
Liquidity incentive program
A Kalshi program that pays for resting orders near the top of the book in eligible markets, filled or not. Kalshi snapshots the book once a second and scores each order by its size and its distance from a reference price. The current terms run to Jan 1, 2027 and exclude FCMs and their customers.
Settlement and rules
Rules
The written terms that decide a market. The primary rules state the condition for YES. The secondary rules cover edge cases. An NFL game market's secondary rules pay $0.50 to each team on a tie and resolve to a fair price if the game does not start within 48 hours.
Source agency
The organization whose published result settles a market, such as a league's official statistics or a government data release. If a source becomes unavailable or changes materially, Rule 7.2 lets Kalshi name a new one.
Close time
When trading stops. After it, Kalshi rejects every order action, including cancels. It removes resting orders shortly after. Markets with can_close_early set to true can close sooner, for example when the outcome is known ahead of schedule.
Expected expiration time
When the outcome is expected to be known. For a game it is usually a few hours after the start. It can fall before the close time, which is often set late to allow for rescheduling.
Latest expiration time
The latest time a market can expire. Rule 7.2 lets Kalshi move expiration when an event is rescheduled or source data is late, with notice on its website.
Determination
The step where Kalshi sets a closed market's result to YES, NO or a scalar value. Kalshi says it takes from about one hour to more than twelve hours after close, mostly depending on when the source publishes.
Settlement timer
The wait between determination and payout, during which the result can be disputed. Its length is set per market and shown in the API as settlement_timer_seconds. When it ends, Kalshi pays out and the market is finalized.
Dispute
A challenge to a result during the settlement timer. The market shows as disputed. If the result changes it shows as amended and the timer restarts. Under Rule 7.1, Kalshi can also send a market to its Outcome Review Committee, which decides within 24 hours with no appeal.
Fair price
A value between $0 and $1 that Kalshi sets when the rules cannot produce a clean YES or NO. Rule 6.3 lets Kalshi use the last traded price, or have the Outcome Review Committee set a fair split.
Last traded price settlement
Rule 6.3(e), for a market whose main subject is a person who dies before expiration. Kalshi may settle at the last traded price before the death, or before the circumstances became known if they moved trading. It took effect Mar 17, 2026.
Settlement
The payout. The winning side receives $1 per contract in cash. Kalshi charges no settlement fee on a plain YES or NO result. Only net positions settle. Kalshi says most markets settle within a few hours of the outcome being known, often within about three hours. How Kalshi settlement works covers each step.
Strategy math
Expected value
The average profit per contract over many repeats of the same trade. For a $1 contract it is your probability p minus the price c minus the fee f.
At a 62% estimate and a 55c taker buy, the fee is about 1.73c and EV is about 5.27c. Expected value in prediction markets has more cases.
Edge
Your probability minus the price, in cents. A 62% estimate against a 55c ask is a 7c gross edge and about 5.27c net of the taker fee. Positive edge can sit on either side of a market, including the less likely one.
Break-even probability
The probability at which expected value is zero. It equals the price plus the fee. At a 55c ask with a 1.73c taker fee it is 56.73%.
Kelly fraction
The share of bankroll that maximizes long-run growth. For a $1 contract at all-in cost c it is (p - c) / (1 - c). At 62% and 56.73c with the fee, full Kelly is 12.2%. See the Kelly criterion guide and the Kelly and EV calculator.
Fractional Kelly
Betting a set share of full Kelly, such as a half or a quarter. It gives up some growth for smaller swings and less harm when your probability is off. Half of the 12.2% example is 6.1%.
Favorite-longshot bias
Cheap contracts winning less often than their price implies, and expensive ones winning slightly more often. A January 2026 University College Dublin study of over 300,000 Kalshi contracts found this pattern. Low-price contracts lost money after fees, and high-price contracts earned small positive returns.
Arbitrage
Related trades that lock in a profit whatever happens. Suppose YES on "Above 3.00" is offered at 40c while someone bids 45c for YES on "Above 3.10" in the same event. Buying the first and selling the second costs 95c and pays at least $1, before fees.
Hedge
A position that offsets a risk you already carry. Kalshi describes hedgers as people exposed to things like inflation, interest rates or hurricanes, who buy contracts that pay when that risk hits.
Regulation and accounts
CFTC
The Commodity Futures Trading Commission: the federal agency that regulates US derivatives markets, Kalshi included. Its glossary defines terms such as contract market, clearing organization and FCM.
Designated contract market
An exchange the CFTC has designated to list futures, options or swaps, known as a DCM. KalshiEX LLC became a DCM on Nov 4, 2020. A DCM must meet the core principles of the Commodity Exchange Act, which include enforcing its own rules and preventing manipulation.
Clearinghouse
A derivatives clearing organization: the firm in the middle of every matched trade. Kalshi Klear LLC got its CFTC registration on Aug 29, 2024 and now clears Kalshi's contracts. Under Rule 6.1 it becomes seller to every buyer and buyer to every seller.
Fully collateralized
A contract whose positions are paid for in full, in cash, up front. Kalshi's event contracts work this way. Buying 100 YES at 55c ties up $55 plus the fee until you sell or the market settles. Rule 6.1 bars any position in these contracts that would expose you beyond the funds in your account.
FCM
A futures commission merchant: a firm that takes orders and accepts funds from customers who trade on an exchange. Kalshi's rulebook lets FCMs bring their customers to the exchange. Those customers reach Kalshi through the FCM and follow its procedures as well as Kalshi's rules.
Rulebook
The KalshiEX LLC Rulebook: the exchange's binding rules on trading, clearing and settlement. Chapter 6 covers settlement and Chapter 7 covers outcome review and contract changes. Kalshi files rule changes with the CFTC.
Subaccount
A separate bucket of cash and positions inside one Direct account. Each Direct account has primary subaccount 0 and can use numbered subaccounts 1 to 63. Subaccounts are an API-only feature for now. Transfers between them stay inside your account.
API key scopes
Permissions on a Kalshi API key. The broad read and write scopes cover every endpoint of that kind. Narrow ones such as write::trade allow orders and RFQs without transfers. A key created without scopes gets full access. See trading Kalshi with the API.
Questions traders ask
What does open interest mean on Kalshi?
Open interest is the number of contracts in a market that are still held and have not settled. Each one has a YES holder and a NO holder and counts once. It rises when two traders open new positions against each other and falls as positions close or settle.
What is the difference between volume and open interest?
Volume counts every contract that has traded. Open interest counts the contracts still held. A market with 10,000 contracts of volume and 500 of open interest has seen heavy trading in and out of a small standing position. Neither figure shows what rests at the current price.
What does a price of 97c mean on Kalshi?
The market prices YES at about 97%. A YES buyer pays 97c to collect $1, so the gain is 3c if right and the loss is 97c if wrong. NO costs about 3c and pays $1 if NO wins. The taker fee on 100 contracts at 97c is about 20c, the same as at 3c.
Is buying NO the same as selling YES on Kalshi?
Yes. Both leave you positioned for NO, and Kalshi treats them as the same trade. A NO bid at 45c is the same order as a YES ask at 55c. Your position in a market is one signed number, so buying NO while you hold YES shrinks the YES position.
What is the difference between a maker and a taker on Kalshi?
A taker's order fills at once against an order already on the book. A maker's order rests first and fills when someone trades against it. Takers pay the standard trading fee. Makers pay nothing on most series and a quarter of the taker rate on series with maker fees.
Sources
- Kalshi API documentation, Kalshi Glossary (accessed Oct 19, 2026)
- Kalshi API documentation, Market Lifecycle (accessed Oct 19, 2026)
- Kalshi API documentation, Market Settlement (accessed Oct 19, 2026)
- Kalshi API documentation, Orderbook Responses (accessed Oct 19, 2026)
- Kalshi API documentation, Order direction (accessed Oct 19, 2026)
- Kalshi API documentation, Fixed-Point Representation (accessed Oct 19, 2026)
- Kalshi API documentation, Fee Rounding (accessed Oct 19, 2026)
- Kalshi API documentation, Create Order (V2) (accessed Oct 19, 2026)
- Kalshi API documentation, Quick Start: Create your first order (accessed Oct 19, 2026)
- Kalshi FIX documentation, Order Entry (accessed Oct 19, 2026)
- Kalshi API documentation, Order Groups (accessed Oct 19, 2026)
- Kalshi API documentation, Request for Quote (RFQ) (accessed Oct 19, 2026)
- Kalshi API documentation, Subaccounts (accessed Oct 19, 2026)
- Kalshi API documentation, Create API Key (accessed Oct 19, 2026)
- Kalshi OpenAPI specification, market, event, series and order fields (accessed Oct 19, 2026)
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- Kalshi public API, rules of a settled NFL game market (accessed Oct 19, 2026)
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- Kalshi Help Center, Collateral Return (accessed Oct 19, 2026)
- Kalshi Help Center, Combos (accessed Oct 19, 2026)
- Kalshi Help Center, Ladder and Escalator Markets (accessed Oct 19, 2026)
- Kalshi Help Center, Market Outcomes (accessed Oct 19, 2026)
- Kalshi Help Center, Market FAQs (accessed Oct 19, 2026)
- Kalshi Help Center, Liquidity Incentive Program (accessed Oct 19, 2026)
- Kalshi Help Center, What is Kalshi Klear (accessed Oct 19, 2026)
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