LZLZL/Prediction markets/Mechanics
FREESEE IT A · MechanicsStart here

You are buying a verdict,
not a stock

2026-08-21 · Start here · enough to read any board

There is no "how far it goes" here. You are buying a claim that will be judged, and at expiry it is worth exactly $1 or $0. The numbers in between — 0.37, 0.62 — are the market's estimate of how likely the claim is to come true. Read this and you should be able to open any board and know what it is saying.

1One board, read out loud

A board asks "will this team win tonight." The screen says 0.62. That is not odds and it is not points. It means: someone will pay 62 cents for the claim that they win.

You payClaim comes trueIt doesn't
Buy YES$0.62get $1 +$0.38get $0 −$0.62
Buy NO$0.38get $0 −$0.38get $1 +$0.62

The two sides add to $1. That is not a coincidence — it is the foundation, and §2 explains it.

One caveat up front"adds to $1" is about settlement value, and that always holds. Quotes on the book need not. There is a spread: the two best bids sum to slightly under $1, the two best asks to slightly over. That gap is one of your costs.

The difference from a stock is the deadline. A stock has no expiry and can print any number. Here, at expiry the price is $1 or $0, necessarily. Everything in between is a temporary state.

2A full set is always worth $1

What you hold is an outcome token. All mutually exclusive outcomes of one event form a complementary set. One rule: at settlement the winning one is worth $1 and every other is worth $0. So whatever happens, a full set is worth exactly $1.

$1 ⇄ one full set of outcome tokens split: $1 buys a set · merge: a set redeems for $1

Both directions are available at any time, without waiting for settlement. Which gives a useful corollary: if you can assemble a full set for less than $1, the difference is free money.

Plenty of people have had that thought, so the lane is picked clean — I censused it and the live opportunity inventory was zero. What matters to you is not the trade; it is that "a set = $1" is the anchor under every price on the venue.

3Price is probability — and it is also your bar

Since the winner pays $1 and the loser pays $0, the fair price of a share is its probability.

0.62 = the market says 62% = your break-even hit rate is 62% the second line is the useful one

Bet repeatedly at that price and you make money above a 62% long-run hit rate and lose below it. Which means "I like this one" is not a statement you can act on. The only actionable question is: is my number higher or lower than 62?

⚠ That bar is the gross one

Taking liquidity costs a fee, so your real bar sits a little above the sticker. Counter-intuitively the fee is heaviest around 50¢ and cheaper toward both tails. The formula and a table are in the taker fee.

Posting liquidity pays no fee at all — so a maker's bar is the sticker price. The cost of that is you may never get filled.

4Not a casino, because there is no house

In a casino your counterparty is the house, the house sets the odds, and the house's expected value is positive by construction.

Here the venue runs a central limit order book: everyone's bids and offers match against each other, so your counterparty is another trader who disagrees with you. The platform does not take the other side. It charges for the match. Nobody sets the price; it is shouted.

SportsbookPrediction market
Counterpartythe houseanother trader
Price set bythe housethe book
Venue earnsthe viga taker fee (makers pay nothing)
Win too muchlimited, then bannednobody has a reason to stop you
Exit earlyusually noyes — if someone will take it
⚠ No vig does not mean cheap

Three costs replace it: the fee (computable), the spread (computable), and the other side knowing more than you (not computable). The first two usually run one to two percent. The third has no ceiling.

A sportsbook at least prints its edge in the odds. Here the edge is inside your counterparty — invisible, but present.

5The seven steps of a trade

StepWatch for
1Fund and approvethe contract needs an allowance before orders go out
2Post or takeposting is free but may never fill; taking is instant and costs
3Fillminimum 5 shares; partial fills are normal
4Holdyou can sell any time — if there is a bid
5The event happens
6Resolutionwho decides, and on what, differs per category
7Redeemthe money does not come back on its own
⚠ Step 7 is the one everybody forgets

After settlement your winning ticket is worth $1 — but it is still a ticket, not a balance. Redeeming is an action you take.

The mirror image is worse: the losing ticket goes to zero and then quietly disappears. It does not leave you a line saying you lost. Anyone adding up their activity feed will therefore overstate themselves. I measured it once and was out by 8× — 589 shares evaporated.

6Four things people get wrong

Commonly saidActually
"0.62 is the platform's odds"it is what another trader will pay; the venue has no view
"being right means making money"depends on the price. Right at 0.95 earns 5%; right at 0.05 pays 20×
"you have to wait for the result"leaving early is normal — thin books permitting
"no house, so it's a fair game"no vig, but fee, spread, and a better-informed counterparty

The second one deserves a sentence of its own. How often you are right does not matter; the price at which you were right does. A 55% judgement is a good business at 0.40 and a losing one at 0.70. Same judgement, different sign.

7One line to keep

You are not buying something that goes up and down. You are buying a claim that will be judged, at a price that is also your break-even bar. So the question worth asking is never "who do I like" — it is "by how much does my number differ from this price, and is that enough to pay the costs."

EvidenceCheck it yourself

A set = $1 split and merge are contract calls with a fixed ratio, visible on-chain at any time.
Order book, not a pool Polymarket runs a CLOB, not an AMM; both sides of the book are public.
Makers pay no fee fee structure and a reconciliation against real fills (predicted $45.23 vs $46.58 received) are in the four rebates.
Minimum 5 shares a matching-layer constraint; smaller orders are rejected or rounded up.
Resolution differs per category read each market's own terms. This site will not do it for you — doing it per category is mandatory, not optional.
Two counter-examples of my own zeroed legs leave no trace (off by 8×) and the settling price is not the price you watch (10.1% measured).
Checked 2026-08. Rules have changed more than once. Verify the current terms before you bet.

NextWhere to go

A · MECHANICS
Price is probability: what 0.62 really says
B · REBATES
Four different things all called "rebate"
G · ENGINEERING
589 shares evaporated
A · MECHANICS
Glossary · EN ⇄ 中文
This is an educational and research record. It is not investment advice, promises no returns, and offers no personalised trading recommendations. Rules and API behaviour are per the official documentation; this page states when it was checked and both can change without notice. Prediction markets are restricted or unavailable in some jurisdictions — confirm your own before taking part.