Definition
YES and NO shares are the two sides of a binary prediction-market contract. A YES share pays $1.00 if the event happens and $0.00 if it does not; a NO share does the reverse. Their prices always sum to $1.00.
YES/NO shares are the basic building block of every binary prediction market. Each contract asks a clear question – will this event happen? – and lets you take either side. Buying YES means you expect it to happen; buying NO means you expect it not to. The format has scaled fast: combined monthly trading volume across prediction venues jumped from $5 billion in September 2025 to a combined $66.7 billion by April 20, 2026 – Kalshi accounting for $37.49 billion of that and Polymarket for $29.23 billion – according to data compiled by SimpleFunctions Substack. Every contract still prices somewhere between $0 and $1 and resolves to a clean $1.00 payout if you call it right, and everything else about trading these markets follows from that simple structure.
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What YES/NO Shares Mean
A binary contract poses a question with two possible answers. “Will Candidate X win the election?” produces two shares: YES and NO. Buying a YES share is a claim that the event will occur; buying a NO share is a claim that it will not. The format has drawn a large and growing user base – Polymarket logged 678,342 monthly active users in April 2026, roughly eight times Kalshi’s implied user base, according to data compiled by LuvKaizen, and the two exchanges’ combined volume has kept climbing: Kalshi and Polymarket together topped $60 billion in volume in 2026, already surpassing their full-year 2025 total of $51 billion, CNBC reported in April 2026. That shift in scale tracks a shift in market share, too – Dune Analytics found Kalshi capturing 62% of weekly volume versus Polymarket’s 37% back in September 2025, and by the end of 2025 the two together controlled roughly 97.5% of sector trading volume, with Kalshi holding an 85% share of sports YES/NO markets versus Polymarket’s 39%, according to data tracked by Jack Haldorsson. Polymarket’s own market pages still put it plainly: a “Yes” share pays $1 and a “No” share pays $0 once the event resolves – and the reverse holds true when No is the correct call.
The prices of the two sides are linked. In a properly priced market they sum to $1.00, because exactly one of them will pay off. If YES trades at $0.70, NO trades at $0.30. That symmetry is what lets you read the price as an implied probability: a YES share at $0.70 says the market puts the chance at 70 percent, and the NO share at $0.30 says the same thing from the other direction. As Eco explained in May 2026, that arithmetic holds across every major venue: binary Yes shares pay $1 if the event happens and No shares pay $1 if it doesn’t, with the two prices always summing to $1.
You do not have to hold a share to resolution. Because prices move continuously, a YES share bought at $0.70 can be sold later at $0.85 to lock in a gain, or at $0.55 to cut a loss, regardless of how the event eventually turns out. That kind of active resale is only possible because liquidity has surged: global monthly volume across prediction markets stood at under $5 billion in September 2025 and climbed to $24 billion by April 2026, according to Pew Research Center, while Kalshi’s own monthly total grew from $1.2 billion in early 2025 to $31.5 billion by March 2026 – jumping 87.4% month-over-month that period on a wave of World Cup YES/NO contracts, per ValueAdd VC – before Kalshi’s volume climbed further to $37.7 billion in July 2026 even as Polymarket’s volume fell 26% to $7.9 billion, according to Dropstab Research, and the combined market (including Polymarket US) then slipped 14.5% to $45.33 billion in August 2026 from July’s total of more than $50 billion, per Datawallet. The share is a tradeable position, not a locked bet.
YES/NO Shares in Practice
Suppose a contract on a hypothetical event lists a YES share at $0.40 and a NO share at $0.60. You buy 100 YES shares. The table traces the two possible outcomes.
| Step | Figure |
|---|---|
| YES price | $0.40 (40% implied) |
| Shares bought | 100 |
| Total cost | $40 |
| If YES wins | $100 back – a $60 profit |
| If NO wins | $0 – the $40 stake is lost |
Notice the maximum loss is fixed at the $40 you paid. You can never lose more than the cost of the position, no matter what happens. The payoff is asymmetric: a cheap YES share that comes good pays a large multiple of its cost, while an expensive one near 90 cents pays little even when you are right. That trade-off between risk and likelihood is the heart of choosing which side to buy. Polymarket’s own “Nothing Ever Happens: 2026” market illustrates the mechanic well: it lists a December 31, 2026 resolution date and, like every binary contract on the platform, pays whichever share turns out correct a flat $1.00. The platform behind it has drawn serious institutional backing to match – ICE committed $2 billion to Polymarket in October 2025 at an $8–9 billion valuation, then added another $600 million in March 2026, according to TokenPost. That scale shows up in the numbers, too: Polymarket’s open interest reached $1.11 billion on May 1, 2026, with Polymarket and Kalshi together holding 98% of the market, per LuvKaizen.
Why It Matters for Traders
YES/NO shares give you defined risk and a direct read on probability. Because you can never lose more than the cost of a position, prediction markets avoid the runaway losses possible in leveraged products. Regulated exchanges are formalizing that same defined-risk structure: Cboe announced a three-outcome settlement framework in March 2026 under which prediction contracts settle to $0, a partial amount, or $100, with the exchange’s first Mini-SPX contract still on track to launch in the second quarter of 2026. That known downside makes position sizing straightforward: the price of the share is the most you can lose per share.
The two-sided structure also means you can express any view. Bullish on an outcome? Buy YES. Bearish? Buy NO. There is no need to find a special “short” instrument – buying NO is the short. That flexibility is one reason the format keeps attracting capital: Kalshi’s own valuation climbed from $5 billion in early 2025 to $11 billion by December 2025, then doubled to $22 billion after a $1 billion raise in March 2026 – a round that landed as the exchange’s annual notional volume surged 1,100% to $23.8 billion for 2025, with weekly volume already topping $500 million in September 2025, per Finance Magnates, and regularly topping $1 billion late in the year, according to AINvest – and by June 2026 the exchange was reportedly negotiating a new round targeting a $40 billion valuation, according to Cryptobriefing. Choosing which side to take, and at what price, is simply a matter of comparing the implied probability against your own estimate.
Related Terms
- Implied Probability – how a share price translates into a percentage chance.
- Settlement – how winning shares are paid $1.00 at resolution.
- How Do Prediction Markets Work – the full beginner primer.
Prediction markets involve financial risk. You can lose the full cost of any position.
